1 00:00:02,000 --> 00:00:07,000 Downloaded from YTS.MX 2 00:00:07,590 --> 00:00:09,926 (wrestlers grunting) 3 00:00:08,000 --> 00:00:13,000 Official YIFY movies site: YTS.MX 4 00:00:10,009 --> 00:00:12,262 NARRATOR: It's one of the largest organs in your body 5 00:00:12,345 --> 00:00:15,724 you can't live without. 6 00:00:15,807 --> 00:00:21,938 Yet many people desperately want to lose their fat. 7 00:00:22,021 --> 00:00:23,732 But fat's been given a bad rap. 8 00:00:23,815 --> 00:00:27,277 We think of fat as being an evil substance, 9 00:00:27,360 --> 00:00:31,156 but fat is life. 10 00:00:31,239 --> 00:00:32,448 SYLVIA TARA: Fat is critical to our health. 11 00:00:32,531 --> 00:00:35,076 It is releasing a whole host of hormones 12 00:00:35,160 --> 00:00:37,579 important for our bones, for our brains, 13 00:00:37,662 --> 00:00:38,705 for our reproductive organs. 14 00:00:38,788 --> 00:00:42,625 Fat is actually a very sophisticated endocrine organ. 15 00:00:42,709 --> 00:00:44,419 DANIEL LIEBERMAN: For millions of years, 16 00:00:44,502 --> 00:00:46,296 people who were able to hold on to their fat 17 00:00:46,379 --> 00:00:47,255 had a selective advantage. 18 00:00:47,338 --> 00:00:49,466 And now all of a sudden, 19 00:00:49,549 --> 00:00:51,968 we've asked people to get rid of their fat. 20 00:00:52,051 --> 00:00:53,970 But our bodies never evolved to do that. 21 00:00:54,053 --> 00:00:58,016 NARRATOR: So, what happens when we have too much fat? 22 00:00:58,099 --> 00:01:01,478 Diabetes, cholesterol issues, heart issues. 23 00:01:01,561 --> 00:01:02,479 DANNY CAHILL: It just sneaks up on you. 24 00:01:02,562 --> 00:01:04,813 It's like smoking cigarettes. 25 00:01:04,897 --> 00:01:07,150 It kills you slowly, you don't feel the pain. 26 00:01:07,233 --> 00:01:08,151 SANA MAHMOOD: I was aware that I was gaining weight, 27 00:01:08,234 --> 00:01:10,487 but I didn't know what to do about it. 28 00:01:10,570 --> 00:01:12,155 I followed every single thing my mom would say. 29 00:01:12,238 --> 00:01:15,200 I exercised for literally an hour daily. 30 00:01:15,283 --> 00:01:18,286 NARRATOR: Do we control our fat? 31 00:01:18,369 --> 00:01:20,205 Or does it control us? 32 00:01:20,288 --> 00:01:24,542 Scientists are finding hormones and genes 33 00:01:24,626 --> 00:01:29,172 that act on the brain to influence our size and shape. 34 00:01:29,255 --> 00:01:33,051 KEVIN HALL: And those biological processes are well beyond willpower. 35 00:01:33,134 --> 00:01:36,179 NARRATOR: The implications are huge 36 00:01:36,262 --> 00:01:38,515 Obesity is the 37 00:01:38,598 --> 00:01:41,017 number one chronic disease that we're dealing with. 38 00:01:41,100 --> 00:01:45,396 NARRATOR: How can science weigh in on our weight problem? 39 00:01:45,479 --> 00:01:47,315 The pieces are starting to fall together-- 40 00:01:47,398 --> 00:01:51,652 signals coming from the body, the brain, and the genes. 41 00:01:51,735 --> 00:01:55,573 It's very complex, but that's exactly what you would expect 42 00:01:55,657 --> 00:01:58,660 for a system which is so critical to survival. 43 00:01:58,743 --> 00:02:01,204 NARRATOR: "The Truth About Fat"-- 44 00:02:01,287 --> 00:02:04,499 right now, on "NOVA." 45 00:02:04,582 --> 00:02:09,711 ♪ ♪ 46 00:02:12,465 --> 00:02:13,758 (announcer speaking Japanese, audience cheers) 47 00:02:13,842 --> 00:02:18,596 NARRATOR: This is Hiroki. 48 00:02:18,680 --> 00:02:21,683 Weighing in at around 550 pounds, 49 00:02:21,766 --> 00:02:23,351 he's about to take on Yama, 50 00:02:23,434 --> 00:02:27,438 a two-time winner of the Sumo World Championship. 51 00:02:30,108 --> 00:02:35,238 Yama is the heaviest Japanese man in history. 52 00:02:35,321 --> 00:02:38,199 Overeating is part of his job. 53 00:02:38,283 --> 00:02:39,909 ANNOUNCER: Everybody say, "Yama"! 54 00:02:39,993 --> 00:02:41,452 AUDIENCE: Yama! 55 00:02:41,536 --> 00:02:46,249 NARRATOR: While an average man eats around 2,500 calories a day, 56 00:02:46,332 --> 00:02:50,211 sumo wrestlers consume up to 10,000. 57 00:02:51,504 --> 00:02:53,590 (men grunting) 58 00:02:53,673 --> 00:02:56,216 Because the heavier you are in sumo, 59 00:02:56,301 --> 00:02:59,095 the harder it is to take you down. 60 00:02:59,178 --> 00:03:01,764 (audience cheering) 61 00:03:01,848 --> 00:03:05,268 For years, doctors wondered why sumo wrestlers, who stay active, 62 00:03:05,351 --> 00:03:09,856 rarely suffer from conditions triggered by obesity. 63 00:03:13,192 --> 00:03:14,652 Answers would come 64 00:03:14,736 --> 00:03:19,616 as new insights radically changed our views of fat. 65 00:03:19,699 --> 00:03:22,327 ♪ ♪ 66 00:03:22,410 --> 00:03:25,288 STEPHEN O'RAHILLY: Most of us think of our fat as our enemy. 67 00:03:25,371 --> 00:03:26,497 It's not, it's our friend. 68 00:03:26,581 --> 00:03:30,960 We need our fat to store any extra calories 69 00:03:31,044 --> 00:03:32,128 so that we can use them in the future 70 00:03:32,211 --> 00:03:35,798 to keep our heart beating, to keep our brain working. 71 00:03:35,882 --> 00:03:38,635 And what's we've been learning over the last 20 years is that 72 00:03:38,718 --> 00:03:42,305 the fat cell isn't just simply a storage organ. 73 00:03:42,388 --> 00:03:45,850 It's a highly intelligent cell talking to our brains. 74 00:03:45,934 --> 00:03:50,103 ♪ ♪ 75 00:03:50,188 --> 00:03:54,817 NARRATOR: So why did body fat evolve in humans? 76 00:03:54,901 --> 00:03:57,612 To understand the forces that shaped us, 77 00:03:57,695 --> 00:04:00,907 a team of scientists have come to Tanzania. 78 00:04:04,911 --> 00:04:07,497 They've set up camp near some of the last hunter-gatherers 79 00:04:07,580 --> 00:04:12,168 on earth, called the Hadza. 80 00:04:12,251 --> 00:04:17,005 ♪ ♪ 81 00:04:17,089 --> 00:04:19,175 HERMAN PONTZER: The human lineage is seven million years old. 82 00:04:19,257 --> 00:04:21,052 And for the last two million years of it, 83 00:04:21,135 --> 00:04:22,512 we've been hunting and gathering. 84 00:04:22,595 --> 00:04:25,807 That's the key innovation of the human species. 85 00:04:25,890 --> 00:04:28,518 And the Hadza are a modern population, 86 00:04:28,601 --> 00:04:30,979 but they keep their old traditions 87 00:04:31,062 --> 00:04:32,480 still very much alive. 88 00:04:32,563 --> 00:04:35,358 And so, this landscape and this lifestyle 89 00:04:35,441 --> 00:04:39,028 is a really good window into our own past. 90 00:04:39,112 --> 00:04:41,572 (people talking in background) 91 00:04:41,656 --> 00:04:44,409 (speaking local language) 92 00:04:44,492 --> 00:04:47,036 NARRATOR: For over a decade, 93 00:04:47,120 --> 00:04:51,541 Herman Pontzer and Brian Wood have been studying the lifestyle 94 00:04:51,624 --> 00:04:53,209 and diet of the Hadza people 95 00:04:53,293 --> 00:04:56,421 to see what it might teach us about modern diseases. 96 00:04:58,631 --> 00:05:00,425 PONTZER: The Hadzas are great models in public health. 97 00:05:00,508 --> 00:05:03,511 They never get heart disease, 98 00:05:03,594 --> 00:05:07,056 they never get diabetes, they're not obese or overweight. 99 00:05:07,140 --> 00:05:09,058 And the diseases that we're most likely to die from 100 00:05:09,142 --> 00:05:13,604 in the U.S. and Europe are not an issue with the Hadza. 101 00:05:13,688 --> 00:05:16,566 If we look at the Hadzas' level of physical activity, 102 00:05:16,649 --> 00:05:18,526 it certainly is quite high 103 00:05:18,609 --> 00:05:21,195 when you compare it to Western, sedentary societies. 104 00:05:21,279 --> 00:05:23,865 They cover more land per day in their travels. 105 00:05:23,948 --> 00:05:26,909 They spend more of their day moving around. 106 00:05:26,993 --> 00:05:29,579 And we know that high levels of physical activity 107 00:05:29,662 --> 00:05:32,623 are certainly protective against major sources of mortality. 108 00:05:32,707 --> 00:05:35,543 (speaking local language) 109 00:05:35,626 --> 00:05:37,503 NARRATOR: With no livestock or crops, 110 00:05:37,587 --> 00:05:42,592 Hadza men and women must forage every day. 111 00:05:42,675 --> 00:05:48,598 Bahati digs for tubers, rich in carbohydrates and fiber, 112 00:05:48,681 --> 00:05:52,643 while other women collect fruit and baobab seeds. 113 00:05:55,271 --> 00:05:59,650 Boys scramble up trees to find bees' nests 114 00:05:59,734 --> 00:06:04,781 and harvest their honey. 115 00:06:04,864 --> 00:06:07,617 But the richest source of calories-- 116 00:06:07,700 --> 00:06:13,122 and the hardest to acquire-- are the meat and fat of animals. 117 00:06:13,206 --> 00:06:14,832 ♪ ♪ 118 00:06:14,916 --> 00:06:16,959 WOOD: Hunting is a risky endeavor. 119 00:06:17,043 --> 00:06:20,254 And that's one of the biggest gambles that you have to take 120 00:06:20,338 --> 00:06:21,631 in this foraging economy, 121 00:06:21,714 --> 00:06:23,966 is you have to get up in the morning and go hunting, 122 00:06:24,050 --> 00:06:27,512 knowing full well that the odds are against you. 123 00:06:29,388 --> 00:06:32,683 NARRATOR: Hadza hunters, like Dofu, use poisoned arrows 124 00:06:32,767 --> 00:06:34,644 to shoot their prey, 125 00:06:34,727 --> 00:06:37,313 but the chase can take hours. 126 00:06:37,396 --> 00:06:39,315 (Dofu speaking local language) 127 00:06:39,398 --> 00:06:42,485 PONTZER: Hunting and gathering takes energy, a lot of it. 128 00:06:42,568 --> 00:06:45,655 (speaking local language) 129 00:06:45,738 --> 00:06:48,032 And so, two million years ago, we start burning more calories, 130 00:06:48,116 --> 00:06:49,784 we get bigger brains. 131 00:06:49,867 --> 00:06:51,661 But the catch is that that 132 00:06:51,744 --> 00:06:53,371 puts us at risk of starving to death. 133 00:06:53,454 --> 00:06:55,039 'Cause if we're burning our engines hotter and faster, 134 00:06:55,123 --> 00:06:56,165 then there's that risk that 135 00:06:56,249 --> 00:06:58,167 you're going to run out of energy. 136 00:06:58,251 --> 00:07:02,130 And so we've evolved fat as the safety net. 137 00:07:02,213 --> 00:07:04,799 (speaking local language) 138 00:07:04,882 --> 00:07:07,677 WOOD: When a man has been lucky enough to kill a large animal, 139 00:07:07,760 --> 00:07:10,471 the first thing he usually does is to pinch its skin 140 00:07:10,555 --> 00:07:11,639 and to see how much fat is on it. 141 00:07:11,722 --> 00:07:15,184 Because that's such a key motivator for their hunting. 142 00:07:15,268 --> 00:07:17,353 And there is no other species 143 00:07:17,436 --> 00:07:19,814 that extracts fat as efficiently from the landscape 144 00:07:19,897 --> 00:07:22,692 as we do. 145 00:07:22,775 --> 00:07:25,653 (speaking local language) 146 00:07:39,292 --> 00:07:41,419 (speaking local language) 147 00:07:41,502 --> 00:07:44,380 ♪ ♪ 148 00:07:44,463 --> 00:07:48,426 NARRATOR: Our body breaks down food into two main sources of energy, 149 00:07:48,509 --> 00:07:50,636 glucose and fat. 150 00:07:50,720 --> 00:07:54,891 Glucose provides immediate fuel 151 00:07:54,974 --> 00:08:00,021 or can be stored as glycogen in our muscles or liver. 152 00:08:00,104 --> 00:08:03,733 As glycogen is depleted, the body burns fat, 153 00:08:03,816 --> 00:08:08,237 which yields, per pound, twice as many calories. 154 00:08:08,321 --> 00:08:13,826 And while humans can only store about a day's worth of glycogen, 155 00:08:13,910 --> 00:08:18,247 we have enough body fat to survive for weeks. 156 00:08:18,331 --> 00:08:23,753 So, think of fat as our battery. 157 00:08:23,836 --> 00:08:26,714 One of the big misconceptions about human evolution 158 00:08:26,797 --> 00:08:28,549 is that we evolved to be healthy. 159 00:08:28,633 --> 00:08:30,259 And the answer is, "Not really." 160 00:08:30,343 --> 00:08:31,802 The only thing that natural selection cares about 161 00:08:31,886 --> 00:08:33,804 is how many offspring you have 162 00:08:33,888 --> 00:08:36,807 who survive and then produce their own offspring. 163 00:08:36,890 --> 00:08:40,311 So, our bodies are beautifully adapted, exquisitely adapted 164 00:08:40,394 --> 00:08:42,855 to take any excess energy and turn it into fat. 165 00:08:42,938 --> 00:08:44,106 Not because it makes us healthy, 166 00:08:44,190 --> 00:08:46,776 but because it helps our reproductive success. 167 00:08:46,859 --> 00:08:52,782 ♪ ♪ 168 00:08:52,865 --> 00:08:57,286 NARRATOR: Fat has long been revered. 169 00:08:57,370 --> 00:09:00,289 One of the earliest representations of obesity 170 00:09:00,373 --> 00:09:04,794 is a statue carved by hunter-gatherers. 171 00:09:04,877 --> 00:09:06,420 Scientists have speculated 172 00:09:06,504 --> 00:09:09,757 that this voluptuous figure symbolized fertility. 173 00:09:13,052 --> 00:09:16,639 O'RAHILLY: Over the centuries, we've had a wide range of views 174 00:09:16,722 --> 00:09:18,766 of what the optimal body shape and the optimal body fatness is, 175 00:09:18,849 --> 00:09:21,811 right, from the Rubenesque period through 176 00:09:21,894 --> 00:09:26,023 to the flappers of the 1920s and the heroin chic of the 1980s. 177 00:09:26,107 --> 00:09:26,983 So, across time, our views 178 00:09:27,066 --> 00:09:30,528 of what is an attractive amount of body fat 179 00:09:30,611 --> 00:09:32,822 has varied enormously. 180 00:09:32,905 --> 00:09:34,699 RANDY SEELEY: Today, as we have stigmatized obesity, 181 00:09:34,782 --> 00:09:37,493 we have demonized fat. 182 00:09:37,576 --> 00:09:39,787 But the ability to be able to store fuel, 183 00:09:39,870 --> 00:09:41,664 so that you can get away from your food supply 184 00:09:41,747 --> 00:09:44,125 for extended periods of time, 185 00:09:44,208 --> 00:09:46,586 allows you to engage in complex behaviors 186 00:09:46,669 --> 00:09:48,963 and the development of the complex cultures 187 00:09:49,046 --> 00:09:50,506 that humans have. 188 00:09:50,589 --> 00:09:53,342 So, fat is a feat of evolution. 189 00:09:53,426 --> 00:09:55,886 It frees us from the tyranny of having to eat continuously. 190 00:09:55,970 --> 00:09:59,348 ♪ ♪ 191 00:09:59,432 --> 00:10:01,851 NARRATOR: Fat cells, called adipocytes, 192 00:10:01,934 --> 00:10:06,063 look like bulbous spheres beneath the microscope. 193 00:10:08,482 --> 00:10:11,861 Inside are droplets of triglycerides, 194 00:10:11,944 --> 00:10:16,073 fats that our body can burn to release vast amounts of energy. 195 00:10:18,242 --> 00:10:22,580 Luckily, fat cells can expand far beyond their normal size 196 00:10:22,663 --> 00:10:25,291 to safely store our excess energy. 197 00:10:29,920 --> 00:10:33,215 So, what would happen if you didn't have any? 198 00:10:33,299 --> 00:10:38,262 Troy Fryer has less than two percent body fat. 199 00:10:39,930 --> 00:10:41,557 Although he looks extremely fit, 200 00:10:41,640 --> 00:10:45,728 it's the of lack fat that makes his muscles stand out. 201 00:10:45,811 --> 00:10:48,898 ♪ ♪ 202 00:10:48,981 --> 00:10:52,318 With no padding on his face, 203 00:10:52,401 --> 00:10:56,489 his cheeks look sunken and his eyes are deeply set. 204 00:10:57,865 --> 00:11:00,743 MAN: How far are you off that way? 205 00:11:00,826 --> 00:11:02,828 The little bit of fat on my body is behind my eyeballs 206 00:11:02,912 --> 00:11:04,914 and on my liver. 207 00:11:04,997 --> 00:11:08,626 So walking around not having fat, 208 00:11:08,709 --> 00:11:12,380 it feels like constant needles 209 00:11:12,463 --> 00:11:14,757 are poking through the bottom of your shoe. 210 00:11:14,840 --> 00:11:17,426 You know some us stand up all day, and we're okay with it. 211 00:11:17,510 --> 00:11:18,302 Troy is not. 212 00:11:18,386 --> 00:11:19,887 Because he has no padding on his feet, 213 00:11:19,970 --> 00:11:23,766 nothing in between his knees. 214 00:11:23,849 --> 00:11:24,934 There's no comfort at all. 215 00:11:25,017 --> 00:11:26,644 (Troy sighs) 216 00:11:26,727 --> 00:11:29,021 It's just unbelievable to watch him struggle. 217 00:11:30,898 --> 00:11:36,862 NARRATOR: Troy was born with a normal amount of fat. 218 00:11:36,946 --> 00:11:40,449 But by age six, he began rapidly losing weight, 219 00:11:40,533 --> 00:11:44,829 despite having a voracious appetite. 220 00:11:44,912 --> 00:11:48,624 I would go through two or three loaves of bread in one day, 221 00:11:48,707 --> 00:11:50,918 making ten sandwiches at a time. 222 00:11:51,001 --> 00:11:52,002 So, I would keep eating and eating and eating 223 00:11:52,086 --> 00:11:54,880 until it would hurt. 224 00:11:54,964 --> 00:11:56,298 And if I didn't get that food, 225 00:11:56,382 --> 00:11:58,634 I would get really upset and really angry. 226 00:11:58,717 --> 00:12:00,136 I would rip doors off their hinges. 227 00:12:00,219 --> 00:12:02,471 I actually sent him in for a psych evaluation, 228 00:12:02,555 --> 00:12:03,931 thinking that there was something wrong 229 00:12:04,014 --> 00:12:06,100 because he couldn't take the answer "No." 230 00:12:06,183 --> 00:12:08,394 It's like he was starving. 231 00:12:10,271 --> 00:12:14,108 NARRATOR: By age nine, Troy was clearly ill. 232 00:12:14,191 --> 00:12:16,652 Doctors were shocked to find 233 00:12:16,735 --> 00:12:18,863 that his blood was full of fat and cholesterol, 234 00:12:18,946 --> 00:12:22,491 symptoms typical of obesity. 235 00:12:24,743 --> 00:12:27,872 It made no sense, until Troy was diagnosed 236 00:12:27,955 --> 00:12:32,793 with a genetic disease called lipodystrophy. 237 00:12:32,877 --> 00:12:36,672 ELIF ORAL: We always think about thinness as something good. 238 00:12:36,755 --> 00:12:37,882 But, in generalized lipodystrophy, 239 00:12:37,965 --> 00:12:40,009 it's beyond thinness. 240 00:12:40,092 --> 00:12:42,470 It's actually absolute 241 00:12:42,553 --> 00:12:44,680 lack of fat under the skin. 242 00:12:44,763 --> 00:12:47,975 So, the excess energy doesn't have a place to go. 243 00:12:50,102 --> 00:12:54,565 NARRATOR: And that's why Troy was sick. 244 00:12:54,648 --> 00:12:59,320 With no fat tissue, excess calories collected in his liver, 245 00:12:59,403 --> 00:13:03,240 enlarging and inflaming it. 246 00:13:03,324 --> 00:13:04,909 SIMON-FRYER: And when it got to that point of the doctor saying, 247 00:13:04,992 --> 00:13:08,204 "There's nothing else we could do for you," 248 00:13:08,287 --> 00:13:09,663 Troy turned to the doctor and said, 249 00:13:09,747 --> 00:13:12,833 "So how and when am I going to die?" 250 00:13:16,170 --> 00:13:19,131 NARRATOR: Salvation would come from the discovery of a mouse 251 00:13:19,215 --> 00:13:23,385 that also couldn't stop eating. 252 00:13:23,469 --> 00:13:27,014 But unlike Troy, this mouse was fat, not thin. 253 00:13:27,097 --> 00:13:29,016 ♪ ♪ 254 00:13:29,099 --> 00:13:32,937 A genetic mutant from a breeding experiment, 255 00:13:33,020 --> 00:13:37,024 it was nicknamed O.B. for obese. 256 00:13:37,107 --> 00:13:40,945 JEFFREY FRIEDMAN: This mouse had a defect in a single gene. 257 00:13:41,028 --> 00:13:42,363 And the impact of that gene was 258 00:13:42,446 --> 00:13:44,198 a mouse that weighed three times normal 259 00:13:44,281 --> 00:13:45,074 and had five times as much fat 260 00:13:45,157 --> 00:13:48,702 and that overate voraciously. 261 00:13:48,786 --> 00:13:52,039 And genetics is very powerful, because what it tells you is 262 00:13:52,122 --> 00:13:55,084 that that obesity has a biological basis. 263 00:13:55,167 --> 00:13:57,086 What that basis is required identifying the gene. 264 00:14:00,214 --> 00:14:01,966 NARRATOR: Scientists began to hunt 265 00:14:02,049 --> 00:14:05,052 for the mutation that made the mouse obese, 266 00:14:05,135 --> 00:14:11,433 combing through the 2.5 billion letters of its genome. 267 00:14:11,517 --> 00:14:13,060 FRIEDMAN: Think of it as an alphabet. 268 00:14:13,143 --> 00:14:14,895 You spell out letters of the genome. 269 00:14:14,979 --> 00:14:18,107 There are four letters, A, G, T, and C. 270 00:14:18,190 --> 00:14:20,568 These spell out-- indirectly-- proteins, 271 00:14:20,651 --> 00:14:23,779 and a single spelling error can lead to a defective gene. 272 00:14:23,862 --> 00:14:25,781 ♪ ♪ 273 00:14:25,864 --> 00:14:29,243 NARRATOR: In 1994, after a decade of work, 274 00:14:29,326 --> 00:14:32,329 Friedman and his collaborators homed in on a gene 275 00:14:32,413 --> 00:14:34,623 only found in fat cells. 276 00:14:34,707 --> 00:14:37,251 ♪ ♪ 277 00:14:37,334 --> 00:14:40,212 FRIEDMAN: That was really the moment of a lifetime. 278 00:14:40,296 --> 00:14:42,464 I pulled out the film with some vague hope 279 00:14:42,548 --> 00:14:43,966 that maybe this would reveal something 280 00:14:44,049 --> 00:14:47,261 about the nature of the O.B. gene. 281 00:14:47,344 --> 00:14:49,471 And I looked at it, and in that instant, I knew 282 00:14:49,555 --> 00:14:51,515 that we had identified the gene 283 00:14:51,599 --> 00:14:54,643 that makes a hormone and that plays a very active role 284 00:14:54,727 --> 00:14:57,479 in regulating appetite, metabolism, 285 00:14:57,563 --> 00:15:02,109 and probably other biological systems. 286 00:15:02,192 --> 00:15:06,322 RUDOLPH LEIBEL: So if you injected that hormone 287 00:15:06,405 --> 00:15:09,450 into the blood of an O.B. mouse, the mouse lost weight. 288 00:15:09,533 --> 00:15:14,496 It would completely cure the mutation of a O.B. mouse. 289 00:15:14,580 --> 00:15:16,457 FRIEDMAN: And over the course of a few weeks, 290 00:15:16,540 --> 00:15:17,541 depending on the dose you give, 291 00:15:17,625 --> 00:15:20,461 they'll look indistinguishable from a normal mouse. 292 00:15:20,544 --> 00:15:24,298 NARRATOR: The hormone was named leptin 293 00:15:24,381 --> 00:15:28,677 from the Greek word leptos, meaning thin. 294 00:15:28,761 --> 00:15:32,264 Its discovery transformed our view of fat 295 00:15:32,348 --> 00:15:37,645 and the biological forces controlling appetite. 296 00:15:37,728 --> 00:15:41,649 The O.B. mouse cannot see itself in a mirror 297 00:15:41,732 --> 00:15:43,275 and realize that it's hugely obese. 298 00:15:43,359 --> 00:15:45,027 It thinks it's starving to death, 299 00:15:45,110 --> 00:15:48,530 because this very critical hormone 300 00:15:48,614 --> 00:15:50,699 is not being made by the body. 301 00:15:50,783 --> 00:15:54,078 And the idea that a hormone produced by fat 302 00:15:54,161 --> 00:15:56,246 can control what you think about food 303 00:15:56,330 --> 00:16:01,085 in a very important way, this is a very radical notion. 304 00:16:01,168 --> 00:16:03,754 (birds chirping) 305 00:16:03,837 --> 00:16:06,882 ♪ ♪ 306 00:16:06,965 --> 00:16:09,677 NARRATOR: Growing up on the outskirts of Chicago, 307 00:16:09,760 --> 00:16:12,721 Sana Mahmood never suspected hormones 308 00:16:12,805 --> 00:16:14,056 might be driving her hunger. 309 00:16:14,139 --> 00:16:17,685 ♪ ♪ 310 00:16:17,768 --> 00:16:19,269 I just thought I didn't have enough willpower in me 311 00:16:19,353 --> 00:16:21,897 to control myself from food. 312 00:16:21,980 --> 00:16:26,110 No matter how much I'd eat, I was starving all the time. 313 00:16:27,319 --> 00:16:30,280 NARRATOR: From infancy, Sana was overweight. 314 00:16:30,364 --> 00:16:36,078 Her parents thought she would soon lose her baby fat, 315 00:16:36,161 --> 00:16:38,622 but she only grew heavier. 316 00:16:41,667 --> 00:16:43,085 MAHMOOD: I'd exercise for an hour daily, 317 00:16:43,168 --> 00:16:44,420 doing, like, kickboxing or treadmill, 318 00:16:44,503 --> 00:16:48,090 or just being as active as I could. 319 00:16:48,173 --> 00:16:50,050 But I didn't know what was going on, 320 00:16:50,134 --> 00:16:51,260 and I was getting scared, 321 00:16:51,343 --> 00:16:54,763 and I would pack on like ten or 20 pounds in a month. 322 00:16:54,847 --> 00:16:56,473 (exhales) 323 00:16:56,557 --> 00:16:58,934 ♪ ♪ 324 00:16:59,017 --> 00:17:00,310 NARRATOR: As Sana struggled with obesity, 325 00:17:00,394 --> 00:17:04,272 she sought help from Dr. Lisa Neff. 326 00:17:07,192 --> 00:17:09,111 Okay, come on in, Sana. 327 00:17:09,194 --> 00:17:10,154 Go ahead and have a seat. Okay. 328 00:17:10,237 --> 00:17:12,156 So this is what we call 329 00:17:12,239 --> 00:17:14,491 an indirect calorimeter. Mm-hmm. 330 00:17:14,575 --> 00:17:15,909 What it's going to do is measure 331 00:17:15,992 --> 00:17:19,329 how many calories your body is burning in a day. 332 00:17:19,413 --> 00:17:22,124 Just breathe normally. Mm-hmm. 333 00:17:22,207 --> 00:17:24,460 NEFF: Sana had tried all different kinds of diets, 334 00:17:24,542 --> 00:17:27,296 exercise programs, medications for weight loss, 335 00:17:27,378 --> 00:17:32,134 and yet she had continued to gain weight. 336 00:17:32,217 --> 00:17:35,804 So, the very first test that I did was a leptin level 337 00:17:35,888 --> 00:17:37,973 in her blood, and it was undetectable. 338 00:17:38,057 --> 00:17:42,311 So, Sana has been fighting hunger her whole life 339 00:17:42,394 --> 00:17:44,396 and it's because she's lacked this critical hormone. 340 00:17:46,315 --> 00:17:48,776 NARRATOR: Like the O.B. mouse, 341 00:17:48,859 --> 00:17:51,320 Sana has a mutated leptin gene, 342 00:17:51,403 --> 00:17:55,699 found so far in just a few dozen people. 343 00:17:55,783 --> 00:17:59,828 A normal fat cell produces leptin, 344 00:17:59,912 --> 00:18:03,499 which travels to the brain and signals the hypothalamus, 345 00:18:03,582 --> 00:18:07,002 a region that determines when and how much we eat. 346 00:18:08,253 --> 00:18:10,297 High levels of leptin tell your brain 347 00:18:10,380 --> 00:18:15,177 you have plenty of fat stored. 348 00:18:15,260 --> 00:18:17,846 But low levels, or in Sana's case, 349 00:18:17,930 --> 00:18:23,393 no leptin at all, triggers an alarm to eat. 350 00:18:23,477 --> 00:18:25,312 First of all, you get the hunger signal. 351 00:18:25,395 --> 00:18:27,898 But secondly, you slow down your metabolic rate. 352 00:18:27,981 --> 00:18:29,191 And if your leptin levels fall even further, 353 00:18:29,274 --> 00:18:31,735 your body says you're starving, 354 00:18:31,819 --> 00:18:34,905 and you do all sorts of things to preserve your life. 355 00:18:34,988 --> 00:18:36,198 You slow down your immune system. 356 00:18:36,281 --> 00:18:37,866 You turn off reproduction 357 00:18:37,950 --> 00:18:40,869 so that you can survive this period of starvation. 358 00:18:40,953 --> 00:18:42,704 So the signals coming from the body 359 00:18:42,788 --> 00:18:44,998 to this bit of the brain called the hypothalamus 360 00:18:45,082 --> 00:18:46,333 are really so powerful. 361 00:18:48,919 --> 00:18:50,838 NARRATOR: Sana is now taking leptin 362 00:18:50,921 --> 00:18:56,051 and has lost 40 pounds in three months. 363 00:18:56,134 --> 00:18:58,053 After taking the leptin, 364 00:18:58,136 --> 00:19:02,724 I've noticed a huge change in my hunger. 365 00:19:02,808 --> 00:19:04,601 I can go four to five hours without eating anything, 366 00:19:04,685 --> 00:19:06,562 and I'll be totally fine. 367 00:19:06,645 --> 00:19:09,398 When I think about the future now, 368 00:19:09,481 --> 00:19:11,400 I'm seeing clear skies everywhere. 369 00:19:11,483 --> 00:19:12,401 My confidence levels have soared. 370 00:19:12,484 --> 00:19:17,739 ♪ ♪ 371 00:19:17,823 --> 00:19:19,366 (birds chirping) 372 00:19:21,869 --> 00:19:22,786 NARRATOR: And for those like Troy, 373 00:19:22,870 --> 00:19:26,373 who can't make leptin because they lack fat, 374 00:19:26,456 --> 00:19:32,087 getting the hormone would be lifesaving. 375 00:19:32,170 --> 00:19:35,257 SIMON-FRYER: The starvation was gone within three days of him taking leptin. 376 00:19:35,340 --> 00:19:37,426 We saved a lot of money. 377 00:19:37,509 --> 00:19:41,555 Troy went from eating what three people would eat, 378 00:19:41,638 --> 00:19:43,640 to eating what a normal person would eat in a day. 379 00:19:43,724 --> 00:19:45,225 You got a little bit of blood on there. 380 00:19:45,309 --> 00:19:47,477 Knowing that I was full, I'm like, 381 00:19:47,561 --> 00:19:49,229 "Wow, this is amazing." 382 00:19:49,313 --> 00:19:51,106 Does it hurt? 383 00:19:51,189 --> 00:19:53,734 NARRATOR: Leptin can't cure Troy's disease, 384 00:19:53,817 --> 00:19:58,405 but by curbing his hunger, it protects his liver. 385 00:19:58,488 --> 00:20:00,782 ORAL: Leptin does not bring the fat back. 386 00:20:00,866 --> 00:20:04,953 It just helps to deal with fat's absence. 387 00:20:05,037 --> 00:20:08,749 Patients finally can take a deep breath 388 00:20:08,832 --> 00:20:11,126 that they're full, 389 00:20:11,209 --> 00:20:12,336 and they don't have to worry about eating. 390 00:20:15,881 --> 00:20:17,466 DONNA RYAN: The discovery of leptin was so exciting. 391 00:20:17,549 --> 00:20:21,386 And the molecule entered into clinical trials in human beings. 392 00:20:21,470 --> 00:20:24,973 And we awaited the results of those trials 393 00:20:25,057 --> 00:20:28,477 with great anticipation, because we thought, "At last 394 00:20:28,560 --> 00:20:30,479 "we have something that's going to cure obesity 395 00:20:30,562 --> 00:20:32,481 in our patients." 396 00:20:32,564 --> 00:20:35,692 That turned out not to be the case. 397 00:20:35,776 --> 00:20:39,321 O'RAHILLY: Most obese people produce plenty of leptin, a lot of it. 398 00:20:39,404 --> 00:20:42,115 And in fact what we found out is that giving more 399 00:20:42,199 --> 00:20:44,660 to people who have plenty doesn't have much of an effect. 400 00:20:44,743 --> 00:20:46,828 ♪ ♪ 401 00:20:46,912 --> 00:20:49,831 NARRATOR: While leptin couldn't cure common obesity, 402 00:20:49,915 --> 00:20:53,502 it revealed that fat was not just a reserve of calories, 403 00:20:53,585 --> 00:20:58,382 but a complex endocrine organ, producing dozens of hormones. 404 00:21:00,425 --> 00:21:01,843 TARA: And those hormones are important 405 00:21:01,927 --> 00:21:04,054 for our bones, for our brains, 406 00:21:04,137 --> 00:21:06,390 for our reproductive organs, for our muscles. 407 00:21:06,473 --> 00:21:07,975 They're important for everything. 408 00:21:08,058 --> 00:21:11,436 And through these hormones, fat can communicate with our bodies. 409 00:21:11,520 --> 00:21:14,856 It can communicate with our brains. 410 00:21:14,940 --> 00:21:16,692 So fat has different roles in our body 411 00:21:16,775 --> 00:21:17,401 at different times of our lives. 412 00:21:17,484 --> 00:21:20,362 (woman talking in background) 413 00:21:20,445 --> 00:21:23,573 NARRATOR: Especially at birth, when a human baby, on average, 414 00:21:23,657 --> 00:21:27,494 has the highest percentage of body fat of any species. 415 00:21:27,577 --> 00:21:31,498 LIEBERMAN: You know, humans really are by far the fattest ape. 416 00:21:31,581 --> 00:21:34,418 A typical human baby is about 15% body fat. 417 00:21:34,501 --> 00:21:38,547 A typical hunter-gatherer male is about ten to 15% body fat, 418 00:21:38,630 --> 00:21:43,093 a typical a hunter-gather female is 15% to 25% body fat. 419 00:21:43,176 --> 00:21:44,428 That's leagues beyond any primate. 420 00:21:44,511 --> 00:21:47,848 ♪ ♪ 421 00:21:47,931 --> 00:21:49,599 NARRATOR: Not only are we fatter than other primates, 422 00:21:49,683 --> 00:21:53,645 we also have bigger brains. 423 00:21:53,729 --> 00:21:56,565 And compared to its body size, 424 00:21:56,648 --> 00:22:01,236 a human baby's brain is massive. 425 00:22:01,319 --> 00:22:04,364 LIEBERMAN: And that brain is consuming half 426 00:22:04,448 --> 00:22:05,907 of that baby's calories, roughly. 427 00:22:05,991 --> 00:22:08,201 That's a lot of energy, right? 428 00:22:08,285 --> 00:22:09,911 And the baby can't stop feeding its brain. 429 00:22:09,995 --> 00:22:12,372 The brain doesn't hold onto energy. 430 00:22:12,456 --> 00:22:15,584 It's a constant, thirsty, demanding organ. 431 00:22:15,667 --> 00:22:20,130 And fat ensures that we always have energy available 432 00:22:20,213 --> 00:22:22,632 to pay for this thirsty organ. 433 00:22:23,842 --> 00:22:26,553 So, when you see a fat, pudgy baby, that's a healthy baby. 434 00:22:26,636 --> 00:22:29,765 Because fat is life, right? 435 00:22:29,848 --> 00:22:32,392 If you don't have enough fat, you're at risk. 436 00:22:32,476 --> 00:22:33,560 (baby and others laughing) 437 00:22:36,688 --> 00:22:39,941 TARA: As we get older, fat plays a role again, 438 00:22:40,025 --> 00:22:41,610 because you need a sufficient amount of fat 439 00:22:41,693 --> 00:22:43,904 to have enough estrogen-- fat produces estrogen. 440 00:22:43,987 --> 00:22:48,241 In fact, girls have to gain on average about 13 pounds or so 441 00:22:48,325 --> 00:22:51,745 before they're able to initiate puberty. 442 00:22:51,828 --> 00:22:53,622 ♪ ♪ 443 00:22:53,705 --> 00:22:59,002 NARRATOR: Model Hartje Andresen never thought much about fat 444 00:22:59,086 --> 00:23:02,130 until she confronted the pressure to be thin. 445 00:23:02,214 --> 00:23:04,800 Will you send me the picture? 446 00:23:04,883 --> 00:23:07,511 ANDRESEN: The photographer who discovered me said, 447 00:23:07,594 --> 00:23:08,595 "You know, you're perfect, 448 00:23:08,678 --> 00:23:11,098 "you're beautiful the way you are. 449 00:23:11,181 --> 00:23:12,599 "But if you get into the modeling industry, 450 00:23:12,682 --> 00:23:15,519 "they are going to tell you to lose weight. 451 00:23:15,602 --> 00:23:18,688 So, my word of advice to you is don't, don't do it." 452 00:23:18,772 --> 00:23:21,024 ♪ ♪ 453 00:23:21,108 --> 00:23:25,070 NARRATOR: But for many models, like Robyn Lawley, 454 00:23:25,153 --> 00:23:27,656 that advice was hard to heed. 455 00:23:27,739 --> 00:23:30,283 Women who walked the runway 456 00:23:30,367 --> 00:23:33,620 had to wear size two or smaller clothing. 457 00:23:36,790 --> 00:23:38,708 It was that heroin chic look at the time. 458 00:23:38,792 --> 00:23:41,711 So, it would be, girls of my height, like six foot, 459 00:23:41,795 --> 00:23:43,672 in a size zero. 460 00:23:43,755 --> 00:23:46,842 So, you had to be emaciated to get that look. 461 00:23:46,925 --> 00:23:48,844 You literally had to starve yourself. 462 00:23:48,927 --> 00:23:51,680 And if you didn't do what you were told, you could be cut. 463 00:23:51,763 --> 00:23:55,016 So, I tried, I lost a bunch of weight, 464 00:23:55,100 --> 00:23:57,185 maintained it all for two minutes, 465 00:23:57,269 --> 00:23:58,562 and then it all came back on again. 466 00:24:00,814 --> 00:24:04,317 NARRATOR: Hartje lost the weight an agency had requested, 467 00:24:04,401 --> 00:24:07,320 getting down to 100 pounds. 468 00:24:09,614 --> 00:24:12,325 But slowly, she began to realize 469 00:24:12,409 --> 00:24:15,787 that being thin was not necessarily healthy. 470 00:24:17,747 --> 00:24:21,418 My hair had really bad quality 471 00:24:21,501 --> 00:24:23,670 and my fingernails were really brittle. 472 00:24:23,753 --> 00:24:28,925 I would get cracked lips and sores at the corner of my mouth, 473 00:24:29,009 --> 00:24:31,595 but the point that made me realize 474 00:24:31,678 --> 00:24:34,014 that maybe I was getting too thin 475 00:24:34,097 --> 00:24:35,807 was when I started breaking my ribs. 476 00:24:35,891 --> 00:24:38,101 ♪ ♪ 477 00:24:38,185 --> 00:24:39,561 LAWLEY: Google "starvation," and that's what happens. 478 00:24:39,644 --> 00:24:42,522 Like, you will lose your period, 479 00:24:42,606 --> 00:24:44,399 you will cause all kinds of diseases 480 00:24:44,482 --> 00:24:47,360 that you never thought would come to you. 481 00:24:47,444 --> 00:24:49,779 ANDRESEN: When I was speaking to my doctor 482 00:24:49,863 --> 00:24:50,780 about wanting to have a baby, 483 00:24:50,864 --> 00:24:53,658 he actually warned me not to be any thinner. 484 00:24:53,742 --> 00:24:57,746 And even though I was exercising a lot, 485 00:24:57,829 --> 00:25:00,707 I was obviously not healthy. 486 00:25:00,790 --> 00:25:04,211 FATIMA CODY STANFORD: If you don't have enough fat stores, 487 00:25:04,294 --> 00:25:06,129 one thing that is affected significantly, 488 00:25:06,213 --> 00:25:07,964 is that we develop issues with bone, 489 00:25:08,048 --> 00:25:09,758 which can then lead to osteoporosis-- 490 00:25:09,841 --> 00:25:11,218 so, actual brittle bones 491 00:25:11,301 --> 00:25:12,761 that have a high susceptibility to breaking. 492 00:25:12,844 --> 00:25:16,556 And so that's something that people might not think about 493 00:25:16,640 --> 00:25:18,934 as we're looking for this aesthetics 494 00:25:19,017 --> 00:25:23,480 of getting to that Twiggy ideal body image. 495 00:25:23,563 --> 00:25:26,733 (audience cheering) 496 00:25:26,816 --> 00:25:30,737 NARRATOR: At the other end of the scale are sumo wrestlers. 497 00:25:30,820 --> 00:25:34,157 (audience cheering) 498 00:25:34,241 --> 00:25:36,284 (men grunting) 499 00:25:36,368 --> 00:25:40,956 Given their massive size, how do they avoid diseases 500 00:25:41,039 --> 00:25:44,167 normally associated with obesity? 501 00:25:44,251 --> 00:25:48,088 (audience cheering) 502 00:25:48,171 --> 00:25:50,674 The answer lies in where they store their fat-- 503 00:25:50,757 --> 00:25:54,219 safely underneath their skin, 504 00:25:54,302 --> 00:25:56,638 instead of in the abdomen or chest, 505 00:25:56,721 --> 00:26:00,850 packed around internal organs. 506 00:26:00,934 --> 00:26:03,520 And so if you do a scan of an active sumo wrestler, 507 00:26:03,603 --> 00:26:07,023 a CT scan or an MRI scan, you'll see all that fat, 508 00:26:07,107 --> 00:26:09,776 but it's on the outside, it's on the buttocks and thighs, 509 00:26:09,859 --> 00:26:11,820 it's on the outside of the abdomen. 510 00:26:11,903 --> 00:26:16,283 CAROLINE APOVIAN: So even though they have body fat, 511 00:26:16,366 --> 00:26:19,286 they don't contain a lot of fat 512 00:26:19,369 --> 00:26:22,330 in those deleterious places such as the liver, 513 00:26:22,414 --> 00:26:25,375 around the heart, around the pancreas, 514 00:26:25,458 --> 00:26:26,209 and even around the kidneys. 515 00:26:26,293 --> 00:26:29,379 So, they're metabolically healthy. 516 00:26:29,462 --> 00:26:34,509 NARRATOR: And the key reason is that sumo wrestlers exercise rigorously, 517 00:26:34,592 --> 00:26:36,845 up to seven hours a day. 518 00:26:38,763 --> 00:26:41,308 TARA: When we exercise, 519 00:26:41,391 --> 00:26:44,102 our fat releases a hormone called adiponectin, 520 00:26:44,185 --> 00:26:47,188 and adiponectin actually helps guide fats in the blood 521 00:26:47,272 --> 00:26:49,065 into safe deposits of fat, 522 00:26:49,149 --> 00:26:51,359 so they'll guide it into subcutaneous fat, 523 00:26:51,443 --> 00:26:52,694 right under the skin. 524 00:26:52,777 --> 00:26:55,238 Interestingly, 525 00:26:55,322 --> 00:26:58,408 when sumo wrestlers come off their exercise regime, 526 00:26:58,491 --> 00:27:00,869 they get metabolically unhealthy very quickly. 527 00:27:00,952 --> 00:27:02,829 (audience applauding) 528 00:27:02,912 --> 00:27:06,041 NARRATOR: To maintain a stable weight, 529 00:27:06,124 --> 00:27:09,252 the number of calories you eat 530 00:27:09,336 --> 00:27:11,880 needs to match the number you burn. 531 00:27:11,963 --> 00:27:15,175 So many assume that losing weight 532 00:27:15,258 --> 00:27:16,760 is simply a matter of eating less 533 00:27:16,843 --> 00:27:21,056 and exercising more. 534 00:27:21,139 --> 00:27:26,394 But scientists are discovering that it's not so simple. 535 00:27:26,478 --> 00:27:28,396 So, what is astonishing is the fact 536 00:27:28,480 --> 00:27:31,107 that we ingest more than a million calories a year. 537 00:27:31,191 --> 00:27:34,069 And yet we don't oscillate between supermodel 538 00:27:34,152 --> 00:27:36,780 and an opera diva over the whole period of a year. 539 00:27:36,863 --> 00:27:39,783 We stay pretty stable. 540 00:27:39,866 --> 00:27:41,576 So I think the best way to think about how weight is regulated 541 00:27:41,659 --> 00:27:43,078 is to think of it as a set point, right? 542 00:27:43,161 --> 00:27:45,372 That is, that our body is defending 543 00:27:45,455 --> 00:27:49,292 a very particular weight under a certain set of circumstances. 544 00:27:49,376 --> 00:27:52,212 LEIBEL: And it's obviously not set 545 00:27:52,295 --> 00:27:54,214 because the body weight can change. 546 00:27:54,297 --> 00:27:56,174 What is set is what is 547 00:27:56,257 --> 00:27:59,928 the minimum body weight for that individual. 548 00:28:00,011 --> 00:28:04,140 If you drop your body weight below this threshold, 549 00:28:04,224 --> 00:28:06,935 the body will begin to do whatever it has to do 550 00:28:07,018 --> 00:28:09,771 to prevent your dying of starvation. 551 00:28:09,854 --> 00:28:11,689 ♪ ♪ 552 00:28:11,773 --> 00:28:13,441 (audience applauding) 553 00:28:13,525 --> 00:28:14,526 NARRATOR: But few Americans grasped 554 00:28:14,609 --> 00:28:17,737 just how hard the body fought against weight loss 555 00:28:17,821 --> 00:28:20,782 until a reality TV show called "The Biggest Loser" 556 00:28:20,865 --> 00:28:22,784 captivated audiences. 557 00:28:22,867 --> 00:28:25,370 Yeah, I made it! 558 00:28:25,453 --> 00:28:28,748 NARRATOR: One of the heaviest contestants on season eight 559 00:28:28,832 --> 00:28:30,458 was Danny Cahill. 560 00:28:30,542 --> 00:28:31,418 Yeah! 561 00:28:33,586 --> 00:28:34,546 NARRATOR: For Danny, 562 00:28:34,629 --> 00:28:37,841 competing on the show was a shot at salvation, 563 00:28:37,924 --> 00:28:40,802 something he had longed for since childhood. 564 00:28:40,885 --> 00:28:43,930 ♪ ♪ 565 00:28:44,013 --> 00:28:45,640 CAHILL: When I was a kid I was like, 566 00:28:45,723 --> 00:28:48,143 if you could have one wish, what would you wish for? 567 00:28:48,226 --> 00:28:50,019 And you know, most people say, "A million dollars," 568 00:28:50,103 --> 00:28:51,312 you know, or-or something. 569 00:28:51,396 --> 00:28:52,939 I'd say, "I wish I could be like that person 570 00:28:53,022 --> 00:28:58,653 that eats the same as me and seems to never gain weight." 571 00:28:58,736 --> 00:29:01,823 NARRATOR: As a child, Danny tended to be heavy, 572 00:29:01,906 --> 00:29:06,828 but by the time he was a father, he struggled with obesity. 573 00:29:06,911 --> 00:29:11,458 His doctor warned that unless he slimmed down, 574 00:29:11,541 --> 00:29:16,504 he might not live to see his kids grow up. 575 00:29:16,588 --> 00:29:18,339 I was mortified at how big I'd gotten. 576 00:29:18,423 --> 00:29:20,508 And it seemed like it happened overnight. 577 00:29:20,592 --> 00:29:22,469 It just sneaks up on you. 578 00:29:22,552 --> 00:29:24,053 You don't feel the pain. 579 00:29:24,137 --> 00:29:25,638 So, when you gain a half a pound 580 00:29:25,722 --> 00:29:28,641 and a half a pound and a half a pound every week, 581 00:29:28,725 --> 00:29:31,311 well, in a year that's 30, 40 pounds. 582 00:29:31,394 --> 00:29:34,355 And in five years, it's a 150 pounds. 583 00:29:34,439 --> 00:29:37,400 (screams) 584 00:29:37,484 --> 00:29:40,361 NARRATOR: Danny saw "The Biggest Loser" as a second chance. 585 00:29:40,445 --> 00:29:42,322 (screaming) 586 00:29:42,405 --> 00:29:44,532 Look at that word, "Believe," okay? 587 00:29:44,616 --> 00:29:48,203 NARRATOR: Cutting calories and exercising around 45 hours each week, 588 00:29:48,286 --> 00:29:50,538 he hoped to shed a pound a day. 589 00:29:50,622 --> 00:29:51,539 TRAINER: Let's go. 590 00:29:51,623 --> 00:29:53,249 Top it. (Cahill grunting) 591 00:29:53,333 --> 00:29:54,292 CAHILL: I went there with a purpose. 592 00:29:54,375 --> 00:29:55,877 I went there to lose the weight. 593 00:29:55,960 --> 00:29:57,837 I went there to break a record. 594 00:29:57,921 --> 00:29:59,380 I went there to-to right my life 595 00:29:59,464 --> 00:30:02,050 and to get the weight that I've been carrying around for years 596 00:30:02,133 --> 00:30:03,384 off of me. 597 00:30:03,468 --> 00:30:05,637 ♪ ♪ 598 00:30:05,720 --> 00:30:08,973 NARRATOR: As the season progressed, Danny pushed harder, 599 00:30:09,057 --> 00:30:12,060 cutting back to 800 calories a day. 600 00:30:12,143 --> 00:30:16,606 Seven months later, when he stepped on the scale 601 00:30:16,689 --> 00:30:18,316 for the final weigh-in, 602 00:30:18,399 --> 00:30:22,070 he had lost a staggering 239 pounds. 603 00:30:22,153 --> 00:30:25,698 (audience applauding) 604 00:30:25,782 --> 00:30:28,076 CAHILL: I was mentally exhausted, I was physically exhausted. 605 00:30:28,159 --> 00:30:32,205 In fact, looking back at it, I go, "How did I do that? 606 00:30:32,288 --> 00:30:33,206 "How did we do that? 607 00:30:33,289 --> 00:30:34,582 That is crazy." 608 00:30:34,666 --> 00:30:35,917 ♪ ♪ 609 00:30:36,000 --> 00:30:40,922 NARRATOR: Danny was determined to keep the weight off at home. 610 00:30:41,005 --> 00:30:43,758 He delayed returning to work 611 00:30:43,841 --> 00:30:46,427 so he could exercise several hours a day. 612 00:30:48,388 --> 00:30:50,098 When his book tour ended, 613 00:30:50,181 --> 00:30:54,727 he went back to his job surveying land. 614 00:30:54,811 --> 00:30:57,105 Moving less and feeling constantly hungry, 615 00:30:57,188 --> 00:31:01,484 the weight came back. 616 00:31:01,568 --> 00:31:06,239 ♪ ♪ 617 00:31:06,322 --> 00:31:11,160 Danny regained over 100 pounds, and he was not alone. 618 00:31:11,244 --> 00:31:16,916 Six years later, N.I.H. scientist Kevin Hall found 619 00:31:17,000 --> 00:31:21,462 that 13 of the 14 contestants he examined 620 00:31:21,546 --> 00:31:23,798 had regained much of their lost weight 621 00:31:23,881 --> 00:31:25,008 or were even heavier. 622 00:31:25,091 --> 00:31:28,303 ♪ ♪ 623 00:31:28,386 --> 00:31:29,804 HALL: When you make extreme changes 624 00:31:29,887 --> 00:31:32,307 to your diet or physical activity patterns, 625 00:31:32,390 --> 00:31:34,142 your body responds very strongly, 626 00:31:34,225 --> 00:31:37,478 both in terms of slowing down the number of calories 627 00:31:37,562 --> 00:31:39,188 that you're burning, as well as 628 00:31:39,272 --> 00:31:41,190 increasing your appetite and hunger. 629 00:31:41,274 --> 00:31:45,320 And those types of processes that are biological, 630 00:31:45,403 --> 00:31:47,322 are well beyond willpower. 631 00:31:47,405 --> 00:31:50,283 Close the door. 632 00:31:50,366 --> 00:31:54,162 NARRATOR: Research has revealed that as dieters lose fat, 633 00:31:54,245 --> 00:31:58,166 leptin levels fall, triggering hunger. 634 00:31:58,249 --> 00:31:59,167 In. 635 00:31:59,250 --> 00:32:01,002 Out. 636 00:32:01,085 --> 00:32:02,670 NARRATOR: As Danny regained weight, 637 00:32:02,754 --> 00:32:05,131 his leptin levels should have rebounded. 638 00:32:05,214 --> 00:32:06,633 But did they? 639 00:32:06,716 --> 00:32:07,967 You started out kind of 640 00:32:08,051 --> 00:32:09,510 more or less where you would expect 641 00:32:09,594 --> 00:32:12,013 for your amount of body fat. 642 00:32:12,096 --> 00:32:13,181 But six years after "The Biggest Loser," 643 00:32:13,264 --> 00:32:14,724 here's where you ended up. 644 00:32:14,807 --> 00:32:16,351 CAHILL: And I was told that that would tell your body 645 00:32:16,434 --> 00:32:19,187 that you're starving and that you needed to eat. 646 00:32:19,270 --> 00:32:21,564 So, how am I going to handle this, 647 00:32:21,648 --> 00:32:24,400 being hungry all the time with my hormone levels out of whack, 648 00:32:24,484 --> 00:32:27,195 and is that ever going to correct itself? 649 00:32:27,278 --> 00:32:31,199 NARRATOR: Thyroid hormones also fell. 650 00:32:31,282 --> 00:32:33,034 And that's one reason 651 00:32:33,117 --> 00:32:35,870 as contestants shed pounds, their metabolic rate-- 652 00:32:35,953 --> 00:32:40,291 the number of calories they burn while resting-- dropped. 653 00:32:41,125 --> 00:32:43,711 HALL: What was the surprise 654 00:32:43,795 --> 00:32:45,213 was that six years later, 655 00:32:45,296 --> 00:32:47,715 their metabolic rate was still at the same level 656 00:32:47,799 --> 00:32:51,260 despite regaining all that body weight. 657 00:32:51,344 --> 00:32:54,305 You started off at zero, basically... 658 00:32:54,389 --> 00:32:56,516 NARRATOR: And compared to other contestants, 659 00:32:56,599 --> 00:32:58,893 after Danny's weight rebounded, 660 00:32:58,976 --> 00:33:02,063 his metabolic rate had fallen the furthest. 661 00:33:02,146 --> 00:33:05,858 Your metabolism was about 800 calories a day lower 662 00:33:05,942 --> 00:33:07,026 than what we would expect. 663 00:33:07,110 --> 00:33:08,111 CAHILL: I was shocked. 664 00:33:08,194 --> 00:33:12,115 My body burned 800 calories less than a normal man 665 00:33:12,198 --> 00:33:14,200 that was the same height and weight. 666 00:33:14,283 --> 00:33:16,077 And I just want people to realize 667 00:33:16,160 --> 00:33:21,165 that obese people aren't just lazy people. 668 00:33:21,249 --> 00:33:23,209 There are a whole lot of things at play here, 669 00:33:23,292 --> 00:33:24,919 and one of them is our biology. 670 00:33:25,002 --> 00:33:28,923 LIEBERMAN: So the vast majority of humans fail on a diet. 671 00:33:29,006 --> 00:33:30,425 And, from an evolutionary perspective, 672 00:33:30,508 --> 00:33:33,928 that makes sense because we never evolved to lose weight. 673 00:33:34,011 --> 00:33:35,430 As soon as you go on a diet, 674 00:33:35,513 --> 00:33:37,932 that activates what's called a starvation response 675 00:33:38,015 --> 00:33:40,393 to help us hold onto energy. 676 00:33:40,476 --> 00:33:43,813 STANFORD: The brain remembers that set point. 677 00:33:43,896 --> 00:33:46,315 The brain is a powerful organ. 678 00:33:46,399 --> 00:33:49,986 And the hypothalamus is powerful in knowing what our weight was. 679 00:33:50,069 --> 00:33:53,281 And so the brain wins. 680 00:33:53,364 --> 00:33:56,242 ♪ ♪ 681 00:33:56,325 --> 00:33:57,952 NARRATOR: There's another reason 682 00:33:58,035 --> 00:34:03,249 why it's hard to voluntarily control your weight. 683 00:34:03,332 --> 00:34:07,170 It's obvious when looking at identical twins, 684 00:34:07,253 --> 00:34:09,797 that the shape and size of their bodies-- 685 00:34:09,880 --> 00:34:15,052 and even their gestures-- are remarkably similar. 686 00:34:15,136 --> 00:34:19,306 That's because they share 100% of their genes. 687 00:34:19,389 --> 00:34:22,310 ♪ ♪ 688 00:34:22,393 --> 00:34:24,603 But that's not true for fraternal twins. 689 00:34:24,687 --> 00:34:25,563 They can differ in gender and size, 690 00:34:25,646 --> 00:34:31,277 because they only share half of their genes. 691 00:34:31,360 --> 00:34:33,279 FRIEDMAN: So if you systematically compare 692 00:34:33,362 --> 00:34:35,947 identical to non-identical twins, 693 00:34:36,032 --> 00:34:36,949 what you conclude is that 694 00:34:37,033 --> 00:34:40,495 obesity is as or more genetic than any trait 695 00:34:40,578 --> 00:34:42,496 that's been studied with the exception of height. 696 00:34:42,580 --> 00:34:44,331 (shouting) 697 00:34:44,415 --> 00:34:46,000 RUTH LOOS: These twin studies have shown 698 00:34:46,083 --> 00:34:50,379 that the heritability of obesity is around 40% to 70%. 699 00:34:50,463 --> 00:34:54,300 So, obesity is not just about the environment, 700 00:34:54,382 --> 00:34:57,011 not just about your lifestyle. 701 00:34:57,094 --> 00:34:59,055 Your genetics determine 702 00:34:59,138 --> 00:35:02,391 why some people gain weight more easily than others. 703 00:35:02,475 --> 00:35:03,351 WOMAN: Jump! 704 00:35:03,434 --> 00:35:07,855 ♪ ♪ 705 00:35:07,939 --> 00:35:10,316 NARRATOR: To find genes that influence obesity, 706 00:35:10,399 --> 00:35:13,528 a global consortium is analyzing genomes 707 00:35:13,611 --> 00:35:15,321 at centers like the Broad Institute. 708 00:35:15,404 --> 00:35:18,032 ♪ ♪ 709 00:35:18,115 --> 00:35:21,077 Over 1,000 genes have been identified 710 00:35:21,160 --> 00:35:24,580 that may play a role in determining weight. 711 00:35:24,664 --> 00:35:28,376 Most are for common obesity and have small effects. 712 00:35:28,459 --> 00:35:31,796 But not all. 713 00:35:32,588 --> 00:35:36,592 The data, mapped to 23 chromosomes, 714 00:35:36,676 --> 00:35:41,264 is publicly available to scientists like Ruth Loos. 715 00:35:41,347 --> 00:35:45,393 As she homes in on a specific location, 716 00:35:45,476 --> 00:35:50,356 she can search for individual genes. 717 00:35:50,439 --> 00:35:53,568 To date, researchers have identified eight different genes 718 00:35:53,651 --> 00:35:57,655 which can cause severe early-onset obesity. 719 00:36:00,283 --> 00:36:03,077 LOOS: And most of these genes, they act in the brain. 720 00:36:03,161 --> 00:36:06,247 They control food intake, they control hunger, 721 00:36:06,330 --> 00:36:08,416 satiety, reward-- 722 00:36:08,499 --> 00:36:10,751 basically components that we can think of 723 00:36:10,835 --> 00:36:14,422 as controlling willpower. 724 00:36:14,505 --> 00:36:16,924 NARRATOR: And there are other gene variants 725 00:36:17,008 --> 00:36:21,929 that don't cause obesity but may make carriers heavier. 726 00:36:22,013 --> 00:36:26,100 One impacts leptin signaling. 727 00:36:26,183 --> 00:36:27,685 LOOS: If you carry that mutation, 728 00:36:27,768 --> 00:36:30,479 then you would weigh about 15 pounds more 729 00:36:30,563 --> 00:36:32,773 than someone who does not. 730 00:36:32,857 --> 00:36:34,859 And we see that one in 5,000 individuals 731 00:36:34,942 --> 00:36:37,612 in the general population carries that mutation. 732 00:36:37,695 --> 00:36:39,280 ♪ ♪ 733 00:36:39,363 --> 00:36:42,909 NARRATOR: But while genes can increase your risk for gaining weight, 734 00:36:42,992 --> 00:36:45,286 they can also protect you. 735 00:36:45,369 --> 00:36:49,290 One gene variant, found in about six percent of the population, 736 00:36:49,373 --> 00:36:54,420 makes carriers always feel full instead of hungry. 737 00:36:54,503 --> 00:36:58,507 O'RAHILLY: Now this variant doesn't make you fat. 738 00:36:58,591 --> 00:37:00,509 It predisposes to making you leaner. 739 00:37:00,593 --> 00:37:03,429 So, we need to understand that there are people 740 00:37:03,512 --> 00:37:07,183 who are very susceptible and people who are very resistant, 741 00:37:07,266 --> 00:37:09,769 that obese people are not morally inferior, 742 00:37:09,852 --> 00:37:11,479 they're biologically different. 743 00:37:14,190 --> 00:37:18,319 NARRATOR: Obesity is defined by your body mass index, or BMI, 744 00:37:18,402 --> 00:37:24,241 a calculation that divides your weight by your height squared. 745 00:37:24,325 --> 00:37:28,621 A BMI above 25 is classified as overweight, 746 00:37:28,704 --> 00:37:31,415 and higher than 30 as obesity. 747 00:37:33,417 --> 00:37:39,674 In the 1980s, obesity rates in the U.S. began rising sharply, 748 00:37:39,757 --> 00:37:45,471 reaching higher than 39% in many states. 749 00:37:45,554 --> 00:37:46,847 STANFORD: Obesity by far 750 00:37:46,931 --> 00:37:49,350 is the greatest public health challenge of our time. 751 00:37:49,433 --> 00:37:52,770 It is the number-one chronic disease 752 00:37:52,853 --> 00:37:55,272 that we're dealing with here in the United States. 753 00:37:55,356 --> 00:37:56,691 And it's leading to at least 754 00:37:56,774 --> 00:38:00,069 a hundred different disease entities that we know of. 755 00:38:00,152 --> 00:38:01,696 RYAN: So we will never 756 00:38:01,779 --> 00:38:03,531 get ahead of diabetes, 757 00:38:03,614 --> 00:38:06,242 we'll never get ahead of cardiovascular disease, 758 00:38:06,325 --> 00:38:07,535 we'll never get ahead of cancer 759 00:38:07,618 --> 00:38:10,579 unless we address the root cause. 760 00:38:10,663 --> 00:38:14,583 And the root cause is, in many cases, obesity. 761 00:38:14,667 --> 00:38:16,877 ♪ ♪ 762 00:38:16,961 --> 00:38:20,548 NARRATOR: And it's not just a U.S. epidemic. 763 00:38:20,631 --> 00:38:26,262 In just three decades, obesity nearly tripled worldwide. 764 00:38:27,805 --> 00:38:29,598 According to the World Health Organization, 765 00:38:29,682 --> 00:38:33,602 one problem might be a decrease in physical activity, 766 00:38:33,686 --> 00:38:36,439 causing us to burn fewer calories. 767 00:38:36,522 --> 00:38:38,566 (phone keyboard clicking) 768 00:38:38,649 --> 00:38:43,487 So is one solution to simply be more active? 769 00:38:45,990 --> 00:38:49,577 ♪ ♪ 770 00:38:49,660 --> 00:38:53,539 Back in Tanzania, Herman Pontzer and Brian Wood, 771 00:38:53,622 --> 00:38:56,542 working with a team of international scientists, 772 00:38:56,625 --> 00:39:00,713 hope to find out. 773 00:39:00,796 --> 00:39:04,592 They're giving members of the Hadza community GPS devices 774 00:39:04,675 --> 00:39:09,263 to measure how far they travel each day. 775 00:39:09,346 --> 00:39:10,931 (Wood speaking local language) 776 00:39:11,015 --> 00:39:12,058 GPS. 777 00:39:12,141 --> 00:39:13,768 NARRATOR: The answer might shed light 778 00:39:13,851 --> 00:39:15,561 on why the Hadza don't suffer 779 00:39:15,644 --> 00:39:19,106 from the chronic diseases seen in the West. 780 00:39:20,649 --> 00:39:21,817 PONTZER: Without antibiotics and vaccines, sadly 781 00:39:21,901 --> 00:39:24,570 a lot of kids, you know, don't make it to their 15th birthday. 782 00:39:24,653 --> 00:39:28,949 But if you make it to 15 in the Hadza population, 783 00:39:29,033 --> 00:39:30,618 there's a great chance you're going to live to be in your 60s, 784 00:39:30,701 --> 00:39:32,995 even 70s and 80s, 785 00:39:33,079 --> 00:39:34,914 and with a much healthier body 786 00:39:34,997 --> 00:39:37,208 than we would often have in the West. 787 00:39:39,376 --> 00:39:42,505 NARRATOR: GPS data reveals why. 788 00:39:42,588 --> 00:39:48,344 Hunters, like Dofu, walk about nine miles a day, 789 00:39:48,427 --> 00:39:52,014 while women foragers walk about five. 790 00:39:52,098 --> 00:39:58,938 That's more exercise than the average American gets in a week. 791 00:39:59,021 --> 00:40:03,526 But do the Hadza people also burn more calories each day? 792 00:40:05,402 --> 00:40:06,695 WOOD: I had spent many months living with the Hadza. 793 00:40:06,779 --> 00:40:09,824 I had gone with them during the day of foraging 794 00:40:09,907 --> 00:40:13,661 and come back to camp, and I felt so tired and exhausted. 795 00:40:13,744 --> 00:40:16,664 I felt of course the energy use that we would be detecting 796 00:40:16,747 --> 00:40:18,666 would be much higher than in Western populations. 797 00:40:18,749 --> 00:40:22,837 (speaking local language) 798 00:40:22,920 --> 00:40:27,007 NARRATOR: To find out, volunteers like Dofu drink a special water 799 00:40:27,091 --> 00:40:29,677 with hydrogen and oxygen molecules that can be traced. 800 00:40:29,760 --> 00:40:32,012 Uh-huh. 801 00:40:32,096 --> 00:40:36,976 NARRATOR: Over the next two weeks, 802 00:40:37,059 --> 00:40:39,895 by tracking the depletion of these molecules, 803 00:40:39,979 --> 00:40:40,521 the scientists can measure the number of calories 804 00:40:40,604 --> 00:40:43,524 burned each day. 805 00:40:43,607 --> 00:40:46,402 PONTZER: So we've come out here, we collect all this data, 806 00:40:46,485 --> 00:40:49,864 you know, putting urine samples on liquid nitrogen, 807 00:40:49,947 --> 00:40:51,907 shipping them to one of the best labs in the country. 808 00:40:51,991 --> 00:40:53,701 And as the results came back, 809 00:40:53,784 --> 00:40:54,702 I wasn't sure what I was seeing at first. 810 00:40:54,785 --> 00:40:57,204 It's, uh, 77. 811 00:40:57,288 --> 00:40:58,664 NARRATOR: Despite being more active, 812 00:40:58,747 --> 00:41:04,587 Hadza men only burn, on average, 2,500 calories per day, 813 00:41:04,670 --> 00:41:08,716 and Hadza women about 1,900, 814 00:41:08,799 --> 00:41:14,471 the same amount as an average man and woman in the U.S. 815 00:41:14,555 --> 00:41:15,806 PONTZER: It's a really counterintuitive result, 816 00:41:15,890 --> 00:41:18,225 and it really surprised us. 817 00:41:18,309 --> 00:41:22,396 Somebody who is sedentary, working a desk job in the U.S., 818 00:41:22,480 --> 00:41:23,731 is burning the same number of calories 819 00:41:23,814 --> 00:41:26,442 as a Hadza man or woman 820 00:41:26,525 --> 00:41:28,444 who's so much more physically active, 821 00:41:28,527 --> 00:41:30,571 and that's even after you account for things 822 00:41:30,654 --> 00:41:34,783 like body size, body composition, age, 823 00:41:34,867 --> 00:41:38,245 gender, all of those factors. 824 00:41:38,329 --> 00:41:42,583 NARRATOR: The research suggests that no matter what our lifestyle is, 825 00:41:42,666 --> 00:41:46,253 our body protects us by keeping the total calories burned 826 00:41:46,337 --> 00:41:50,549 each day within a narrow range. 827 00:41:50,633 --> 00:41:53,636 And that's why, in the long run, 828 00:41:53,719 --> 00:41:59,266 exercise alone won't make you thin. 829 00:41:59,350 --> 00:42:01,310 PONTZER: I think what the Hadza data tell us 830 00:42:01,393 --> 00:42:04,647 is that we can change our lifestyles however we want, 831 00:42:04,730 --> 00:42:07,149 and more activity is always better, 832 00:42:07,233 --> 00:42:09,109 but it's not going to burn more calories, 833 00:42:09,193 --> 00:42:13,614 'cause our bodies adjust to these more-active lifestyles. 834 00:42:13,697 --> 00:42:16,784 NARRATOR: The implications are huge. 835 00:42:16,867 --> 00:42:20,246 If obesity is not due to sedentary lifestyles, 836 00:42:20,329 --> 00:42:25,584 it must be caused by eating too many calories. 837 00:42:25,668 --> 00:42:28,796 And according to Daniel Lieberman, 838 00:42:28,879 --> 00:42:32,800 that became possible as humans changed their environment. 839 00:42:32,883 --> 00:42:37,429 LIEBERMAN: So in the last 10,000 years we've transformed 840 00:42:37,513 --> 00:42:39,807 both how we get energy, actually, and how we use energy. 841 00:42:39,890 --> 00:42:41,684 And the first big shift occurred with the origins of agriculture, 842 00:42:41,767 --> 00:42:45,521 when we shifted from simply going out and getting food 843 00:42:45,604 --> 00:42:48,440 out there in nature to growing the food ourselves. 844 00:42:50,651 --> 00:42:55,030 NARRATOR: Farming allowed humans to grow carbohydrate-rich foods 845 00:42:55,114 --> 00:42:59,702 like corn, wheat, and rice. 846 00:42:59,785 --> 00:43:01,996 And then we invented machines 847 00:43:02,079 --> 00:43:05,666 and industrialized how we grow food. 848 00:43:05,749 --> 00:43:09,878 We've increased the scale of calories that we produce 849 00:43:09,962 --> 00:43:12,756 by orders of magnitude. 850 00:43:12,840 --> 00:43:16,302 And the result is, for the first time in millions of years, 851 00:43:16,385 --> 00:43:18,429 we have more energy than we know what to do with. 852 00:43:18,512 --> 00:43:21,140 ♪ ♪ 853 00:43:21,223 --> 00:43:25,644 NARRATOR: And it's not just an excess of calories. 854 00:43:25,728 --> 00:43:26,812 Scientists suspect that obesity may be caused 855 00:43:26,895 --> 00:43:30,858 by the changing nature of the foods we eat. 856 00:43:30,941 --> 00:43:32,860 ♪ ♪ 857 00:43:32,943 --> 00:43:34,820 More than 50% of calories in the U.S. 858 00:43:34,903 --> 00:43:38,741 are consumed in the form of ultra-processed foods, 859 00:43:38,824 --> 00:43:43,704 low in fiber, but full of fat, sugar, and salt. 860 00:43:43,787 --> 00:43:49,877 Packed with calories, they've been labeled obesogenic. 861 00:43:49,960 --> 00:43:53,172 But do they cause us to overeat? 862 00:43:53,255 --> 00:43:57,760 To find out, Nora Volkow has been scanning the brains 863 00:43:57,843 --> 00:44:00,929 of patients with and without obesity. 864 00:44:03,974 --> 00:44:07,186 VOLKOW: To me the most important aspect about obesity 865 00:44:07,269 --> 00:44:09,688 is understanding that 866 00:44:09,772 --> 00:44:12,566 the food itself has made changes in your brain 867 00:44:12,649 --> 00:44:15,402 that are driving your inability to stop eating. 868 00:44:15,486 --> 00:44:17,738 ♪ ♪ 869 00:44:17,821 --> 00:44:19,531 NARRATOR: These changes begin 870 00:44:19,615 --> 00:44:22,576 as food activates our brain's reward system, 871 00:44:22,659 --> 00:44:26,246 releasing a feel-good chemical called dopamine. 872 00:44:27,956 --> 00:44:30,918 Through pleasure, dopamine motivates us 873 00:44:31,001 --> 00:44:34,922 to find and eat rewarding foods. 874 00:44:35,005 --> 00:44:38,967 Imaging reveals that high-fat, sugary foods 875 00:44:39,051 --> 00:44:42,137 can overwhelm the brain's reward system, 876 00:44:42,221 --> 00:44:45,808 flooding it with too much dopamine. 877 00:44:45,891 --> 00:44:49,770 VOLKOW: Our bodies actually have evolved 878 00:44:49,853 --> 00:44:53,107 to try to maintain a homeostatic state. 879 00:44:53,190 --> 00:44:55,984 And that means that if there's too much stimulation 880 00:44:56,068 --> 00:44:59,905 with dopamine, you start to see that receptors 881 00:44:59,988 --> 00:45:03,242 that are sensitive to dopamine 882 00:45:03,325 --> 00:45:05,244 are downregulated, they decrease. 883 00:45:05,327 --> 00:45:07,955 ♪ ♪ 884 00:45:08,038 --> 00:45:10,165 NARRATOR: Volkow found that dopamine receptors, 885 00:45:10,249 --> 00:45:13,460 seen as red in the brains of control subjects, 886 00:45:13,544 --> 00:45:18,132 are reduced in people with obesity. 887 00:45:18,215 --> 00:45:21,301 VOLKOW: As dopamine signaling goes down, 888 00:45:21,385 --> 00:45:26,974 our capacity to be able to inhibit desires goes down. 889 00:45:27,057 --> 00:45:31,019 So, I say, "I'm not going to eat the chocolate, 890 00:45:31,103 --> 00:45:33,188 "or I'm not going to eat the donut. 891 00:45:33,272 --> 00:45:35,315 I don't want to eat it." 892 00:45:35,399 --> 00:45:36,608 Can I stop it? 893 00:45:36,692 --> 00:45:41,321 And if those areas of the brain are not functioning properly, 894 00:45:41,405 --> 00:45:46,452 no matter how much you want not to do something, 895 00:45:46,535 --> 00:45:48,495 it's very difficult to carry through. 896 00:45:48,579 --> 00:45:51,957 And this explains why people will tell you, 897 00:45:52,040 --> 00:45:54,001 "I did not want to eat the food. 898 00:45:54,084 --> 00:45:56,879 "I knew I was going to gain the weight. 899 00:45:56,962 --> 00:45:59,840 Yet I could not stop myself." 900 00:45:59,923 --> 00:46:00,924 ♪ ♪ 901 00:46:01,008 --> 00:46:04,887 NARRATOR: The truth about fat is complicated. 902 00:46:04,970 --> 00:46:10,267 Evolution has designed powerful hormonal and neural signals 903 00:46:10,350 --> 00:46:15,105 to ensure that we eat and defend our weight. 904 00:46:17,316 --> 00:46:19,902 RYAN: I think what people really need to understand about obesity 905 00:46:19,985 --> 00:46:22,029 is that it's not your fault. 906 00:46:22,112 --> 00:46:25,866 This is not a matter of your willpower. 907 00:46:25,949 --> 00:46:28,035 This is a disease. 908 00:46:28,118 --> 00:46:30,496 It's a chronic disease. 909 00:46:30,579 --> 00:46:32,581 It's a highly complex disease, 910 00:46:32,664 --> 00:46:34,082 and there are many causes of obesity. 911 00:46:36,001 --> 00:46:42,424 NARRATOR: So, can obesity be prevented or treated? 912 00:46:42,508 --> 00:46:43,800 The experts say maybe, 913 00:46:43,884 --> 00:46:48,597 using a long-term approach, focused on health. 914 00:46:48,680 --> 00:46:51,058 STANFORD: I don't want to put you on the next diet. 915 00:46:51,141 --> 00:46:53,894 Diet implies that it's short term. 916 00:46:53,977 --> 00:46:55,938 I want to put you on a lifestyle plan 917 00:46:56,021 --> 00:46:58,649 that you can sustain for years. 918 00:46:58,732 --> 00:47:00,400 TRAINER: In place. 919 00:47:00,484 --> 00:47:04,404 NARRATOR: While "The Biggest Loser" reveals why diets fail, 920 00:47:04,488 --> 00:47:06,907 contestants like Danny-- who continue to exercise-- 921 00:47:06,990 --> 00:47:12,079 kept off ten to 13% of their weight. 922 00:47:12,162 --> 00:47:13,956 And medically, that's a success, 923 00:47:14,039 --> 00:47:18,126 because modest weight loss has huge health benefits, 924 00:47:18,210 --> 00:47:22,923 from lowering blood pressure to preventing diabetes. 925 00:47:23,006 --> 00:47:28,679 There're also medications that signal the brain to feel full, 926 00:47:28,762 --> 00:47:33,934 and help people lose ten percent of their weight. 927 00:47:34,017 --> 00:47:36,937 And if you want to lose 100 pounds or more, 928 00:47:37,020 --> 00:47:39,106 there's another option, 929 00:47:39,189 --> 00:47:44,695 one that Muriel Mena chose to avoid the fate of her mother. 930 00:47:46,863 --> 00:47:50,951 MENA: I was three, and I remember she was talking on the phone, 931 00:47:51,034 --> 00:47:55,080 and she collapsed because she had a heart attack. 932 00:47:55,163 --> 00:48:00,419 And then I just remember E.M.T.s rushing in. 933 00:48:00,502 --> 00:48:05,757 NARRATOR: At age 44, Muriel's mom weighed 300 pounds 934 00:48:05,841 --> 00:48:08,802 and had died of heart disease. 935 00:48:08,885 --> 00:48:12,973 As an adolescent, Muriel began struggling with her weight, 936 00:48:13,056 --> 00:48:15,976 just as her mother had. 937 00:48:16,059 --> 00:48:19,980 MENA: I was going to the doctor's and having to get my heart checked, 938 00:48:20,063 --> 00:48:21,189 and I was like, "Wait, this is weird. 939 00:48:21,273 --> 00:48:23,817 Like, I'm 13 at a cardiologist." 940 00:48:23,900 --> 00:48:25,527 It was always in the back of my mind, 941 00:48:25,611 --> 00:48:29,448 "Oh, this is what she passed from." 942 00:48:29,531 --> 00:48:34,453 NARRATOR: By age 16, Muriel, like nearly five million American teenagers, 943 00:48:34,536 --> 00:48:38,373 had obesity, and qualified for bariatric surgery, 944 00:48:38,457 --> 00:48:42,169 which bypasses or removes part of the stomach. 945 00:48:42,252 --> 00:48:47,507 APOVIAN: Bariatric surgery is the only way 946 00:48:47,591 --> 00:48:50,177 that most people with severe obesity 947 00:48:50,260 --> 00:48:54,681 can not just lose weight but most importantly keep it off. 948 00:48:57,100 --> 00:48:59,061 So you've been doing great. 949 00:48:59,144 --> 00:49:01,605 The first thing I want to show you is 950 00:49:01,688 --> 00:49:04,191 275 was your highest weight. 951 00:49:04,274 --> 00:49:07,861 Your body mass index was 43. 952 00:49:07,944 --> 00:49:12,532 After surgery you went all the way down to 172 pounds 953 00:49:12,616 --> 00:49:14,326 and a BMI of about 28. 954 00:49:14,409 --> 00:49:17,245 And that's really fantastic. 955 00:49:17,329 --> 00:49:22,876 Originally we thought that bariatric surgery worked 956 00:49:22,959 --> 00:49:25,212 by making the stomach much smaller, 957 00:49:25,295 --> 00:49:27,839 so that you couldn't eat a lot of food. 958 00:49:27,923 --> 00:49:31,385 We now know that the hormones that come from the G.I. tract 959 00:49:31,468 --> 00:49:33,720 and go to the brain change in a way 960 00:49:33,804 --> 00:49:39,518 that cause satiety earlier, sooner, and with much less food. 961 00:49:39,601 --> 00:49:44,815 NARRATOR: These signal changes between the gut and brain 962 00:49:44,898 --> 00:49:48,276 help the body reset its set point for years. 963 00:49:48,360 --> 00:49:53,198 But hunger can return, 964 00:49:53,281 --> 00:49:54,074 because our weight is as regulated 965 00:49:54,157 --> 00:49:59,746 as our blood pressure and heartbeat. 966 00:49:59,830 --> 00:50:00,956 The ability to control our weight 967 00:50:01,039 --> 00:50:04,000 is distinctly outside our conscious control. 968 00:50:04,084 --> 00:50:05,585 People don't like to hear that. 969 00:50:05,669 --> 00:50:07,087 We all want to think that we're in control 970 00:50:07,170 --> 00:50:08,213 of when we put the fork down. 971 00:50:08,296 --> 00:50:10,298 But there are lots of biological forces 972 00:50:10,382 --> 00:50:15,387 that are controlling what weight it is that you end up at. 973 00:50:15,470 --> 00:50:18,098 TARA: Fat behaves differently on all of us. 974 00:50:18,181 --> 00:50:19,266 It has to do with our genetics. 975 00:50:19,349 --> 00:50:21,643 It has to do with our age, our gender, 976 00:50:21,727 --> 00:50:22,310 a whole host of factors. 977 00:50:22,394 --> 00:50:27,149 Everybody is very different. 978 00:50:27,232 --> 00:50:29,109 And what matters is to be healthy, 979 00:50:29,192 --> 00:50:31,486 not to be perfect. 980 00:50:31,570 --> 00:50:32,738 (laughs) 981 00:50:32,821 --> 00:50:37,784 NARRATOR: Today, Hartje Andresen is 20 pounds heavier, 982 00:50:37,868 --> 00:50:40,787 a mother, and modeling on her own terms. 983 00:50:40,871 --> 00:50:42,706 (camera shutter clicking) 984 00:50:42,789 --> 00:50:46,126 ANDRESEN: I had to overcome this fear of gaining weight, 985 00:50:46,209 --> 00:50:48,962 and that really took some courage for me. 986 00:50:49,045 --> 00:50:51,256 ♪ ♪ 987 00:50:51,339 --> 00:50:53,300 Modeling has the possibility 988 00:50:53,383 --> 00:50:57,596 to show people how a healthy body should look like. 989 00:50:59,389 --> 00:51:03,477 The focus needs to be more on strength and health 990 00:51:03,560 --> 00:51:07,105 rather than being a certain size. 991 00:51:07,189 --> 00:51:09,107 ♪ ♪ 992 00:51:09,191 --> 00:51:12,486 NARRATOR: And there's another insight provided by the Hadza, 993 00:51:12,569 --> 00:51:15,530 and hunters like Dofu. 994 00:51:15,614 --> 00:51:18,867 PONTZER: What the Hadza tell us is that 995 00:51:18,950 --> 00:51:21,828 diet and exercise are two different tools 996 00:51:21,912 --> 00:51:23,163 with two different jobs. 997 00:51:23,246 --> 00:51:25,999 You need to exercise to stay healthy 998 00:51:26,082 --> 00:51:27,334 and to age well, 999 00:51:27,417 --> 00:51:29,836 but you need to watch your diet 1000 00:51:29,920 --> 00:51:32,005 if you want to watch your weight. 1001 00:51:32,088 --> 00:51:34,216 LIEBERMAN: It's not a coincidence that 1002 00:51:34,299 --> 00:51:36,384 the obesity epidemic is spreading around the world. 1003 00:51:36,468 --> 00:51:40,806 Wherever modern, Western, post-industrial lifestyles 1004 00:51:40,889 --> 00:51:43,642 show up, obesity follows with them. 1005 00:51:43,725 --> 00:51:45,894 But I don't think the solution is to go back to the Stone Age. 1006 00:51:45,977 --> 00:51:49,356 I think the solution is to learn from our evolutionary history 1007 00:51:49,439 --> 00:51:52,567 and get the best of both worlds.