1 00:00:09,768 --> 00:00:13,013 It's one of the largest organs in your body 2 00:00:13,047 --> 00:00:15,532 you can't live without. 3 00:00:15,567 --> 00:00:21,711 Yet many people desperately want to lose their fat. 4 00:00:21,745 --> 00:00:23,540 But fat's been given a bad rap. 5 00:00:23,575 --> 00:00:28,028 We think of fat as being an evil substance, 6 00:00:28,062 --> 00:00:31,100 but fat is life. 7 00:00:31,134 --> 00:00:32,342 Fat is critical to our health. 8 00:00:32,377 --> 00:00:34,827 It is releasing a whole host of hormones 9 00:00:34,862 --> 00:00:37,416 important for our bones, for our brains, 10 00:00:37,451 --> 00:00:38,900 for our reproductive organs. 11 00:00:38,935 --> 00:00:42,490 Fat is actually a very sophisticated endocrine organ. 12 00:00:42,525 --> 00:00:44,285 For millions of years, 13 00:00:44,320 --> 00:00:46,218 people who were able to hold on to their fat 14 00:00:46,253 --> 00:00:47,978 had a selective advantage. 15 00:00:48,013 --> 00:00:49,359 And now all of a sudden, 16 00:00:49,394 --> 00:00:51,741 we've asked people to get rid of their fat. 17 00:00:51,775 --> 00:00:53,743 But our bodies never evolved to do that. 18 00:00:53,777 --> 00:00:57,816 So, what happens when we have too much fat? 19 00:00:57,850 --> 00:01:01,337 Diabetes, cholesterol issues, heart issues. 20 00:01:01,371 --> 00:01:02,372 It just sneaks up on you. 21 00:01:02,407 --> 00:01:04,616 It's like smoking cigarettes. 22 00:01:04,650 --> 00:01:07,101 It kills you slowly, you don't feel the pain. 23 00:01:07,136 --> 00:01:08,930 I was aware that I was gaining weight, 24 00:01:08,965 --> 00:01:10,346 but I didn't know what to do about it. 25 00:01:10,380 --> 00:01:12,934 I followed every single thing my mom would say. 26 00:01:12,969 --> 00:01:15,144 I exercised for literally an hour daily. 27 00:01:15,178 --> 00:01:18,181 Do we control our fat? 28 00:01:18,216 --> 00:01:20,977 Or does it control us? 29 00:01:21,011 --> 00:01:24,429 Scientists are finding hormones and genes 30 00:01:24,463 --> 00:01:28,916 that act on the brain to influence our size and shape. 31 00:01:28,950 --> 00:01:32,851 And those biological processes are well beyond willpower. 32 00:01:32,885 --> 00:01:36,958 The implications are huge 33 00:01:36,993 --> 00:01:38,374 Obesity is the 34 00:01:38,408 --> 00:01:40,824 number one chronic disease that we're dealing with. 35 00:01:40,859 --> 00:01:45,312 How can science weigh in on our weight problem? 36 00:01:45,346 --> 00:01:47,210 The pieces are starting to fall together... 37 00:01:47,245 --> 00:01:51,490 signals coming from the body, the brain, and the genes. 38 00:01:51,525 --> 00:01:55,460 It's very complex, but that's exactly what you would expect 39 00:01:55,494 --> 00:01:58,497 for a system which is so critical to survival. 40 00:01:58,532 --> 00:02:01,983 "The Truth About Fat"... 41 00:02:02,018 --> 00:02:04,365 right now, on "NOVA." 42 00:02:13,650 --> 00:02:18,483 This is Hiroki. 43 00:02:18,517 --> 00:02:21,520 Weighing in at around 550 pounds, 44 00:02:21,555 --> 00:02:24,074 he's about to take on Yama, 45 00:02:24,109 --> 00:02:28,113 a two-time winner of the Sumo World Championship. 46 00:02:29,839 --> 00:02:35,189 Yama is the heaviest Japanese man in history. 47 00:02:35,224 --> 00:02:37,950 Overeating is part of his job. 48 00:02:37,985 --> 00:02:39,711 Everybody say, "Yama"! 49 00:02:39,745 --> 00:02:41,368 Yama! 50 00:02:41,402 --> 00:02:47,028 While an average man eats around 2,500 calories a day, 51 00:02:47,063 --> 00:02:49,928 sumo wrestlers consume up to 10,000. 52 00:02:53,518 --> 00:02:55,968 Because the heavier you are in sumo, 53 00:02:56,003 --> 00:02:58,868 the harder it is to take you down. 54 00:03:01,629 --> 00:03:06,047 For years, doctors wondered why sumo wrestlers, who stay active, 55 00:03:06,082 --> 00:03:09,637 rarely suffer from conditions triggered by obesity. 56 00:03:12,951 --> 00:03:14,539 Answers would come 57 00:03:14,573 --> 00:03:19,475 as new insights radically changed our views of fat. 58 00:03:22,305 --> 00:03:25,239 Most of us think of our fat as our enemy. 59 00:03:25,274 --> 00:03:27,241 It's not, it's our friend. 60 00:03:27,276 --> 00:03:30,796 We need our fat to store any extra calories 61 00:03:30,831 --> 00:03:32,142 so that we can use them in the future 62 00:03:32,177 --> 00:03:35,663 to keep our heart beating, to keep our brain working. 63 00:03:35,698 --> 00:03:38,494 And what's we've been learning over the last 20 years is that 64 00:03:38,528 --> 00:03:42,049 the fat cell isn't just simply a storage organ. 65 00:03:42,083 --> 00:03:45,708 It's a highly intelligent cell talking to our brains. 66 00:03:49,919 --> 00:03:54,648 So why did body fat evolve in humans? 67 00:03:54,682 --> 00:03:57,478 To understand the forces that shaped us, 68 00:03:57,513 --> 00:04:00,688 a team of scientists have come to Tanzania. 69 00:04:04,692 --> 00:04:08,248 They've set up camp near some of the last hunter-gatherers 70 00:04:08,282 --> 00:04:11,975 on earth, called the Hadza. 71 00:04:16,877 --> 00:04:18,982 The human lineage is seven million years old. 72 00:04:19,017 --> 00:04:20,881 And for the last two million years of it, 73 00:04:20,915 --> 00:04:23,263 we've been hunting and gathering. 74 00:04:23,297 --> 00:04:25,644 That's the key innovation of the human species. 75 00:04:25,679 --> 00:04:29,269 And the Hadza are a modern population, 76 00:04:29,303 --> 00:04:30,787 but they keep their old traditions 77 00:04:30,822 --> 00:04:33,203 still very much alive. 78 00:04:33,238 --> 00:04:35,309 And so, this landscape and this lifestyle 79 00:04:35,344 --> 00:04:38,830 is a really good window into our own past. 80 00:04:44,387 --> 00:04:46,872 For over a decade, 81 00:04:46,907 --> 00:04:51,429 Herman Pontzer and Brian Wood, have been studying the lifestyle 82 00:04:51,463 --> 00:04:52,982 and diet of the Hadza people 83 00:04:53,016 --> 00:04:56,296 to see what it might teach us about modern diseases. 84 00:04:58,505 --> 00:05:00,369 The Hadzas are great models in public health. 85 00:05:00,403 --> 00:05:03,406 They never get heart disease, 86 00:05:03,441 --> 00:05:06,892 they never get diabetes, they're not obese or overweight. 87 00:05:06,927 --> 00:05:08,860 And the diseases that we're most likely to die from 88 00:05:08,894 --> 00:05:13,520 in the U.S. and Europe are not an issue with the Hadza. 89 00:05:13,554 --> 00:05:16,454 If we look at the Hadzas' level of physical activity, 90 00:05:16,488 --> 00:05:18,421 it certainly is quite high 91 00:05:18,456 --> 00:05:20,975 when you compare it to Western, sedentary societies. 92 00:05:21,010 --> 00:05:23,702 They cover more land per day in their travels. 93 00:05:23,737 --> 00:05:26,774 They spend more of their day moving around. 94 00:05:26,809 --> 00:05:29,467 And we know that high levels of physical activity 95 00:05:29,501 --> 00:05:33,367 are certainly protective against major sources of mortality. 96 00:05:36,301 --> 00:05:38,234 With no livestock or crops, 97 00:05:38,268 --> 00:05:42,514 Hadza men and women must forage every day. 98 00:05:42,549 --> 00:05:49,314 Bahati digs for tubers, rich in carbohydrates and fiber, 99 00:05:49,349 --> 00:05:53,318 while other women collect fruit and baobab seeds. 100 00:05:55,009 --> 00:05:59,566 Boys scramble up trees to find bees' nests 101 00:05:59,600 --> 00:06:04,674 and harvest their honey. 102 00:06:04,709 --> 00:06:08,368 But the richest source of calories... 103 00:06:08,402 --> 00:06:12,924 and the hardest to acquire... are the meat and fat of animals. 104 00:06:14,753 --> 00:06:16,790 Hunting is a risky endeavor. 105 00:06:16,824 --> 00:06:20,034 And that's one of the biggest gambles that you have to take 106 00:06:20,069 --> 00:06:21,553 in this foraging economy, 107 00:06:21,588 --> 00:06:23,797 is you have to get up in the morning and go hunting, 108 00:06:23,831 --> 00:06:27,387 knowing full well that the odds are against you. 109 00:06:29,147 --> 00:06:32,599 Hadza hunters, like Dofu, use poisoned arrows 110 00:06:32,633 --> 00:06:34,532 to shoot their prey, 111 00:06:34,566 --> 00:06:37,086 but the chase can take hours. 112 00:06:39,122 --> 00:06:42,436 Hunting and gathering takes energy, a lot of it. 113 00:06:45,577 --> 00:06:47,890 And so, two million years ago, we start burning more calories, 114 00:06:47,924 --> 00:06:49,650 we get bigger brains. 115 00:06:49,685 --> 00:06:51,549 But the catch is that that 116 00:06:51,583 --> 00:06:53,171 puts us at risk of starving to death. 117 00:06:53,205 --> 00:06:54,897 'Cause if we're burning our engines hotter and faster, 118 00:06:54,931 --> 00:06:56,001 then there's that risk that 119 00:06:56,036 --> 00:06:57,969 you're going to run out of energy. 120 00:06:58,003 --> 00:07:01,938 And so we've evolved fat as the safety net. 121 00:07:04,700 --> 00:07:07,599 When a man has been lucky enough to kill a large animal, 122 00:07:07,634 --> 00:07:10,222 the first thing he usually does is to pinch its skin 123 00:07:10,257 --> 00:07:12,293 and to see how much fat is on it. 124 00:07:12,328 --> 00:07:14,986 Because that's such a key motivator for their hunting. 125 00:07:15,020 --> 00:07:17,160 And there is no other species 126 00:07:17,195 --> 00:07:19,680 that extracts fat as efficiently from the landscape 127 00:07:19,715 --> 00:07:22,580 as we do. 128 00:07:44,187 --> 00:07:48,226 Our body breaks down food into two main sources of energy, 129 00:07:48,260 --> 00:07:51,367 glucose and fat. 130 00:07:51,401 --> 00:07:54,750 Glucose provides immediate fuel 131 00:07:54,784 --> 00:07:59,858 or can be stored as glycogen in our muscles or liver. 132 00:07:59,893 --> 00:08:03,655 As glycogen is depleted, the body burns fat, 133 00:08:03,690 --> 00:08:08,073 which yields, per pound, twice as many calories. 134 00:08:08,108 --> 00:08:13,700 And while humans can only store about a day's worth of glycogen, 135 00:08:13,734 --> 00:08:18,083 we have enough body fat to survive for weeks. 136 00:08:18,118 --> 00:08:23,675 So, think of fat as our battery. 137 00:08:23,710 --> 00:08:26,609 One of the big misconceptions about human evolution 138 00:08:26,644 --> 00:08:28,300 is that we evolved to be healthy. 139 00:08:28,335 --> 00:08:30,095 And the answer is, "Not really." 140 00:08:30,130 --> 00:08:32,546 The only thing that natural selection cares about 141 00:08:32,581 --> 00:08:34,548 is how many offspring you have 142 00:08:34,583 --> 00:08:36,723 who survive and then produce their own offspring. 143 00:08:36,757 --> 00:08:40,140 So, our bodies are beautifully adapted, exquisitely adapted 144 00:08:40,174 --> 00:08:42,729 to take any excess energy and turn it into fat. 145 00:08:42,763 --> 00:08:43,971 Not because it makes us healthy, 146 00:08:44,006 --> 00:08:46,664 but because it helps our reproductive success. 147 00:08:52,704 --> 00:08:57,122 Fat has long been revered. 148 00:08:57,157 --> 00:09:00,125 One of the earliest representations of obesity 149 00:09:00,160 --> 00:09:04,682 is a statue carved by hunter-gatherers. 150 00:09:04,716 --> 00:09:06,200 Scientists have speculated 151 00:09:06,235 --> 00:09:10,446 that this voluptuous figure symbolized fertility. 152 00:09:12,897 --> 00:09:16,383 Over the centuries, we've had a wide range of views 153 00:09:16,417 --> 00:09:19,489 of what the optimal body shape and the optimal body fatness is, 154 00:09:19,524 --> 00:09:22,527 right, from the Rubenesque period through 155 00:09:22,562 --> 00:09:25,910 to the flappers of the 1920s and the heroin chic of the 1980s. 156 00:09:25,944 --> 00:09:27,497 So, across time, our views 157 00:09:27,532 --> 00:09:30,328 of what is an attractive amount of body fat 158 00:09:30,362 --> 00:09:32,710 has varied enormously. 159 00:09:32,744 --> 00:09:35,471 Today, as we have stigmatized obesity, 160 00:09:35,505 --> 00:09:37,300 we have demonized fat. 161 00:09:37,335 --> 00:09:39,682 But the ability to be able to store fuel, 162 00:09:39,717 --> 00:09:42,443 so that you can get away from your food supply 163 00:09:42,478 --> 00:09:43,962 for extended periods of time, 164 00:09:43,997 --> 00:09:46,344 allows you to engage in complex behaviors 165 00:09:46,378 --> 00:09:48,829 and the development of the complex cultures 166 00:09:48,864 --> 00:09:50,313 that humans have. 167 00:09:50,348 --> 00:09:53,144 So, fat is a feat of evolution. 168 00:09:53,178 --> 00:09:56,630 It frees us from the tyranny of having to eat continuously. 169 00:09:59,184 --> 00:10:02,567 Fat cells, called adipocytes, 170 00:10:02,602 --> 00:10:05,881 look like bulbous spheres beneath the microscope. 171 00:10:08,262 --> 00:10:11,783 Inside are droplets of triglycerides, 172 00:10:11,818 --> 00:10:15,891 fats that our body can burn to release vast amounts of energy. 173 00:10:18,031 --> 00:10:22,380 Luckily, fat cells can expand far beyond their normal size 174 00:10:22,414 --> 00:10:25,072 to safely store our excess energy. 175 00:10:29,767 --> 00:10:33,046 So, what would happen if you didn't have any? 176 00:10:33,080 --> 00:10:38,051 Troy Fryer has less than two percent body fat. 177 00:10:39,777 --> 00:10:41,364 Although he looks extremely fit, 178 00:10:41,399 --> 00:10:45,679 it's the of lack fat that makes his muscles stand out. 179 00:10:49,649 --> 00:10:52,134 With no padding on his face, 180 00:10:52,168 --> 00:10:56,241 his cheeks look sunken and his eyes are deeply set. 181 00:10:58,588 --> 00:11:00,487 How far are you off that way? 182 00:11:00,521 --> 00:11:03,559 The little bit of fat on my body is behind my eyeballs 183 00:11:03,593 --> 00:11:04,836 and on my liver. 184 00:11:04,871 --> 00:11:08,426 So walking around not having fat, 185 00:11:08,460 --> 00:11:12,188 it feels like constant needles 186 00:11:12,223 --> 00:11:14,501 are poking through the bottom of your shoe. 187 00:11:14,535 --> 00:11:17,228 You know some us stand up all day, and we're okay with it. 188 00:11:17,262 --> 00:11:18,608 Troy is not. 189 00:11:18,643 --> 00:11:20,610 Because he has no padding on his feet, 190 00:11:20,645 --> 00:11:23,510 nothing in between his knees. 191 00:11:23,544 --> 00:11:24,856 There's no comfort at all. 192 00:11:26,478 --> 00:11:29,689 It's just unbelievable to watch him struggle. 193 00:11:31,621 --> 00:11:36,765 Troy was born with a normal amount of fat. 194 00:11:36,799 --> 00:11:40,251 But by age six, he began rapidly losing weight, 195 00:11:40,285 --> 00:11:45,601 despite having a voracious appetite. 196 00:11:45,635 --> 00:11:48,431 I would go through two or three loaves of bread in one day, 197 00:11:48,466 --> 00:11:50,813 making ten sandwiches at a time. 198 00:11:50,848 --> 00:11:52,746 So, I would keep eating and eating and eating 199 00:11:52,781 --> 00:11:54,783 until it would hurt. 200 00:11:54,817 --> 00:11:56,163 And if I didn't get that food, 201 00:11:56,198 --> 00:11:58,407 I would get really upset and really angry. 202 00:11:58,441 --> 00:12:00,029 I would rip doors off their hinges. 203 00:12:00,064 --> 00:12:02,273 I actually sent him in for a psych evaluation, 204 00:12:02,307 --> 00:12:03,826 thinking that there was something wrong 205 00:12:03,861 --> 00:12:05,966 because he couldn't take the answer "No." 206 00:12:06,001 --> 00:12:08,175 It's like he was starving. 207 00:12:10,108 --> 00:12:13,974 By age nine, Troy was clearly ill. 208 00:12:14,009 --> 00:12:16,459 Doctors were shocked to find 209 00:12:16,494 --> 00:12:19,635 that his blood was full of fat and cholesterol, 210 00:12:19,669 --> 00:12:22,258 symptoms typical of obesity. 211 00:12:24,502 --> 00:12:27,816 It made no sense, until Troy was diagnosed 212 00:12:27,850 --> 00:12:32,544 with a genetic disease called lipodystrophy. 213 00:12:32,579 --> 00:12:36,445 We always think about thinness as something good. 214 00:12:36,479 --> 00:12:38,654 But, in generalized lipodystrophy, 215 00:12:38,688 --> 00:12:40,760 it's beyond thinness. 216 00:12:40,794 --> 00:12:42,278 It's actually absolute 217 00:12:42,313 --> 00:12:44,453 lack of fat under the skin. 218 00:12:44,487 --> 00:12:48,664 So, the excess energy doesn't have a place to go. 219 00:12:50,804 --> 00:12:54,394 And that's why Troy was sick. 220 00:12:54,428 --> 00:12:59,157 With no fat tissue, excess calories collected in his liver, 221 00:12:59,192 --> 00:13:03,127 enlarging and inflaming it. 222 00:13:03,161 --> 00:13:05,681 And when it got to that point of the doctor saying, 223 00:13:05,715 --> 00:13:08,063 "There's nothing else we could do for you," 224 00:13:08,097 --> 00:13:09,443 Troy turned to the doctor and said, 225 00:13:09,478 --> 00:13:12,550 "So how and when am I going to die?" 226 00:13:16,036 --> 00:13:19,833 Salvation would come from the discovery of a mouse 227 00:13:19,868 --> 00:13:23,216 that also couldn't stop eating. 228 00:13:23,250 --> 00:13:27,737 But unlike Troy, this mouse was fat, not thin. 229 00:13:29,774 --> 00:13:32,881 A genetic mutant from a breeding experiment, 230 00:13:32,915 --> 00:13:36,919 it was nicknamed O.B. for obese. 231 00:13:36,954 --> 00:13:40,889 This mouse had a defect in a single gene. 232 00:13:40,923 --> 00:13:42,200 And the impact of that gene was 233 00:13:42,235 --> 00:13:44,064 a mouse that weighed three times normal 234 00:13:44,099 --> 00:13:45,790 and had five times as much fat 235 00:13:45,825 --> 00:13:48,482 and that overate voraciously. 236 00:13:48,517 --> 00:13:51,934 And genetics is very powerful, because what it tells you is 237 00:13:51,969 --> 00:13:55,006 that that obesity has a biological basis. 238 00:13:55,041 --> 00:13:57,767 What that basis is required identifying the gene. 239 00:14:00,080 --> 00:14:01,910 Scientists began to hunt 240 00:14:01,944 --> 00:14:05,775 for the mutation that made the mouse obese, 241 00:14:05,810 --> 00:14:11,298 combing through the 2.5 billion letters of its genome. 242 00:14:11,333 --> 00:14:12,955 Think of it as an alphabet. 243 00:14:12,990 --> 00:14:14,646 You spell out letters of the genome. 244 00:14:14,681 --> 00:14:17,995 There are four letters, A, G, T, and C. 245 00:14:18,029 --> 00:14:20,376 These spell out... indirectly... proteins, 246 00:14:20,411 --> 00:14:23,586 and a single spelling error can lead to a defective gene. 247 00:14:25,588 --> 00:14:29,109 In 1994, after a decade of work, 248 00:14:29,144 --> 00:14:32,216 Friedman and his collaborators homed in on a gene 249 00:14:32,250 --> 00:14:34,459 only found in fat cells. 250 00:14:37,152 --> 00:14:40,086 That was really the moment of a lifetime. 251 00:14:40,120 --> 00:14:42,329 I pulled out the film with some vague hope 252 00:14:42,364 --> 00:14:44,745 that maybe this would reveal something 253 00:14:44,780 --> 00:14:47,127 about the nature of the O.B. gene. 254 00:14:47,162 --> 00:14:49,336 And I looked at it, and in that instant, I knew 255 00:14:49,371 --> 00:14:51,373 that we had identified the gene 256 00:14:51,407 --> 00:14:54,445 that makes a hormone and that plays a very active role 257 00:14:54,479 --> 00:14:57,310 in regulating appetite, metabolism, 258 00:14:57,344 --> 00:15:02,004 and probably other biological systems. 259 00:15:02,039 --> 00:15:06,215 So if you injected that hormone 260 00:15:06,250 --> 00:15:09,287 into the blood of an O.B. mouse, the mouse lost weight. 261 00:15:09,322 --> 00:15:14,327 It would completely cure the mutation of a O.B. mouse. 262 00:15:14,361 --> 00:15:16,294 And over the course of a few weeks, 263 00:15:16,329 --> 00:15:17,917 depending on the dose you give, 264 00:15:17,951 --> 00:15:20,298 they'll look indistinguishable from a normal mouse. 265 00:15:20,333 --> 00:15:24,164 The hormone was named leptin 266 00:15:24,199 --> 00:15:28,513 from the Greek word leptos, meaning thin. 267 00:15:28,548 --> 00:15:32,138 Its discovery transformed our view of fat 268 00:15:32,172 --> 00:15:37,453 and the biological forces controlling appetite. 269 00:15:37,488 --> 00:15:41,457 The O.B. mouse cannot see itself in a mirror 270 00:15:41,492 --> 00:15:43,977 and realize that it's hugely obese. 271 00:15:44,012 --> 00:15:45,806 It thinks it's starving to death, 272 00:15:45,841 --> 00:15:48,361 because this very critical hormone 273 00:15:48,395 --> 00:15:50,535 is not being made by the body. 274 00:15:50,570 --> 00:15:54,022 And the idea that a hormone produced by fat 275 00:15:54,056 --> 00:15:56,990 can control what you think about food 276 00:15:57,025 --> 00:16:01,029 in a very important way, this is a very radical notion. 277 00:16:06,724 --> 00:16:09,485 Growing up on the outskirts of Chicago, 278 00:16:09,520 --> 00:16:12,523 Sana Mahmood never suspected hormones 279 00:16:12,557 --> 00:16:14,007 might be driving her hunger. 280 00:16:17,528 --> 00:16:20,013 I just thought I didn't have enough willpower in me 281 00:16:20,048 --> 00:16:21,670 to control myself from food. 282 00:16:21,704 --> 00:16:25,985 No matter how much I'd eat, I was starving all the time. 283 00:16:28,021 --> 00:16:31,024 From infancy, Sana was overweight. 284 00:16:31,059 --> 00:16:36,029 Her parents thought she would soon lose her baby fat, 285 00:16:36,064 --> 00:16:38,411 but she only grew heavier. 286 00:16:41,448 --> 00:16:42,829 I'd exercise for an hour daily, 287 00:16:42,863 --> 00:16:44,313 doing, like, kickboxing or treadmill, 288 00:16:44,348 --> 00:16:48,041 or just being as active as I could. 289 00:16:48,076 --> 00:16:49,801 But I didn't know what was going on, 290 00:16:49,836 --> 00:16:51,148 and I was getting scared, 291 00:16:51,182 --> 00:16:54,565 and I would pack on like ten or 20 pounds in a month. 292 00:16:58,741 --> 00:17:01,054 As Sana struggled with obesity, 293 00:17:01,089 --> 00:17:04,954 she sought help from Dr. Lisa Neff. 294 00:17:06,887 --> 00:17:08,855 Okay, come on in, Sana. 295 00:17:08,889 --> 00:17:10,926 Go ahead and have a seat. Okay. 296 00:17:10,960 --> 00:17:12,928 So this is what we call 297 00:17:12,962 --> 00:17:14,378 an indirect calorimeter. Mm-hmm. 298 00:17:14,412 --> 00:17:15,689 What it's going to do is measure 299 00:17:15,724 --> 00:17:19,245 how many calories your body is burning in a day. 300 00:17:19,279 --> 00:17:21,868 Just breathe normally. Mm-hmm. 301 00:17:21,902 --> 00:17:24,319 Sana had tried all different kinds of diets, 302 00:17:24,353 --> 00:17:28,047 exercise programs, medications for weight loss, 303 00:17:28,081 --> 00:17:31,878 and yet she had continued to gain weight. 304 00:17:31,912 --> 00:17:35,640 So, the very first test that I did was a leptin level 305 00:17:35,675 --> 00:17:37,746 in her blood, and it was undetectable. 306 00:17:37,780 --> 00:17:43,062 So, Sana has been fighting hunger her whole life 307 00:17:43,096 --> 00:17:45,064 and it's because she's lacked this critical hormone. 308 00:17:46,996 --> 00:17:48,584 Like the O.B. mouse, 309 00:17:48,619 --> 00:17:51,208 Sana has a mutated leptin gene, 310 00:17:51,242 --> 00:17:55,557 found so far in just a few dozen people. 311 00:17:55,591 --> 00:17:59,664 A normal fat cell produces leptin, 312 00:17:59,699 --> 00:18:03,358 which travels to the brain and signals the hypothalamus, 313 00:18:03,392 --> 00:18:06,740 a region that determines when and how much we eat. 314 00:18:08,984 --> 00:18:11,020 High levels of leptin tell your brain 315 00:18:11,055 --> 00:18:14,921 you have plenty of fat stored. 316 00:18:14,955 --> 00:18:17,682 But low levels, or in Sana's case, 317 00:18:17,717 --> 00:18:23,309 no leptin at all, triggers an alarm to eat. 318 00:18:23,343 --> 00:18:25,207 First of all, you get the hunger signal. 319 00:18:25,242 --> 00:18:27,727 But secondly, you slow down your metabolic rate. 320 00:18:27,761 --> 00:18:29,970 And if your leptin levels fall even further, 321 00:18:30,005 --> 00:18:31,593 your body says you're starving, 322 00:18:31,627 --> 00:18:34,734 and you do all sorts of things to preserve your life. 323 00:18:34,768 --> 00:18:36,149 You slow down your immune system. 324 00:18:36,184 --> 00:18:37,668 You turn off reproduction 325 00:18:37,702 --> 00:18:40,671 so that you can survive this period of starvation. 326 00:18:40,705 --> 00:18:42,535 So the signals coming from the body 327 00:18:42,569 --> 00:18:44,778 to this bit of the brain called the hypothalamus 328 00:18:44,813 --> 00:18:46,194 are really so powerful. 329 00:18:48,679 --> 00:18:50,646 Sana is now taking leptin 330 00:18:50,681 --> 00:18:55,824 and has lost 40 pounds in three months. 331 00:18:55,858 --> 00:18:57,860 After taking the leptin, 332 00:18:57,895 --> 00:19:02,589 I've noticed a huge change in my hunger. 333 00:19:02,624 --> 00:19:04,488 I can go four to five hours without eating anything, 334 00:19:04,522 --> 00:19:06,455 and I'll be totally fine. 335 00:19:06,490 --> 00:19:09,286 When I think about the future now, 336 00:19:09,320 --> 00:19:11,288 I'm seeing clear skies everywhere. 337 00:19:11,322 --> 00:19:13,152 My confidence levels have soared. 338 00:19:21,677 --> 00:19:23,023 And for those like Troy, 339 00:19:23,058 --> 00:19:27,096 who can't make leptin because they lack fat, 340 00:19:27,131 --> 00:19:31,860 getting the hormone would be lifesaving. 341 00:19:31,894 --> 00:19:35,208 The starvation was gone within three days of him taking leptin. 342 00:19:35,243 --> 00:19:37,348 We saved a lot of money. 343 00:19:37,383 --> 00:19:41,421 Troy went from eating what three people would eat, 344 00:19:41,456 --> 00:19:43,527 to eating what a normal person would eat in a day. 345 00:19:43,561 --> 00:19:44,976 You got a little bit of blood on there. 346 00:19:45,011 --> 00:19:47,393 Knowing that I was full, I'm like, 347 00:19:47,427 --> 00:19:48,980 "Wow, this is amazing." 348 00:19:49,015 --> 00:19:50,879 Does it hurt? 349 00:19:50,913 --> 00:19:53,571 Leptin can't cure Troy's disease, 350 00:19:53,606 --> 00:19:58,300 but by curbing his hunger, it protects his liver. 351 00:19:58,335 --> 00:20:00,613 Leptin does not bring the fat back. 352 00:20:00,647 --> 00:20:04,755 It just helps to deal with fat's absence. 353 00:20:04,789 --> 00:20:08,586 Patients finally can take a deep breath 354 00:20:08,621 --> 00:20:10,933 that they're full, 355 00:20:10,968 --> 00:20:13,039 and they don't have to worry about eating. 356 00:20:15,662 --> 00:20:18,182 The discovery of leptin was so exciting. 357 00:20:18,217 --> 00:20:22,117 And the molecule entered into clinical trials in human beings. 358 00:20:22,151 --> 00:20:24,775 And we awaited the results of those trials 359 00:20:24,809 --> 00:20:28,365 with great anticipation, because we thought, "At last 360 00:20:28,399 --> 00:20:31,195 "we have something that's going to cure obesity 361 00:20:31,230 --> 00:20:33,232 in our patients." 362 00:20:33,266 --> 00:20:35,579 That turned out not to be the case. 363 00:20:35,613 --> 00:20:39,272 Most obese people produce plenty of leptin, a lot of it. 364 00:20:39,307 --> 00:20:41,895 And in fact what we found out is that giving more 365 00:20:41,930 --> 00:20:44,553 to people who have plenty doesn't have much of an effect. 366 00:20:46,693 --> 00:20:49,696 While leptin couldn't cure common obesity, 367 00:20:49,731 --> 00:20:54,218 it revealed that fat was not just a reserve of calories, 368 00:20:54,253 --> 00:20:59,085 but a complex endocrine organ, producing dozens of hormones. 369 00:21:00,328 --> 00:21:01,708 And those hormones are important 370 00:21:01,743 --> 00:21:03,883 for our bones, for our brains, 371 00:21:03,917 --> 00:21:06,334 for our reproductive organs, for our muscles. 372 00:21:06,368 --> 00:21:07,783 They're important for everything. 373 00:21:07,818 --> 00:21:11,339 And through these hormones, fat can communicate with our bodies. 374 00:21:11,373 --> 00:21:14,721 It can communicate with our brains. 375 00:21:14,756 --> 00:21:16,585 So fat has different roles in our body 376 00:21:16,620 --> 00:21:18,173 at different times of our lives. 377 00:21:20,348 --> 00:21:23,489 Especially at birth, when a human baby, on average, 378 00:21:23,523 --> 00:21:28,217 has the highest percentage of body fat of any species. 379 00:21:28,252 --> 00:21:32,221 You know, humans really are by far the fattest ape. 380 00:21:32,256 --> 00:21:35,190 A typical human baby is about 15% body fat. 381 00:21:35,224 --> 00:21:39,263 A typical hunter-gatherer male is about ten to 15% body fat, 382 00:21:39,298 --> 00:21:42,922 a typical a hunter-gather female is 15% to 25% body fat. 383 00:21:42,956 --> 00:21:45,200 That's leagues beyond any primate. 384 00:21:47,720 --> 00:21:50,343 Not only are we fatter than other primates, 385 00:21:50,378 --> 00:21:54,347 we also have bigger brains. 386 00:21:54,382 --> 00:21:56,453 And compared to its body size, 387 00:21:56,487 --> 00:22:01,043 a human baby's brain is massive. 388 00:22:01,078 --> 00:22:04,115 And that brain is consuming half 389 00:22:04,150 --> 00:22:05,738 of that baby's calories, roughly. 390 00:22:05,772 --> 00:22:07,981 That's a lot of energy, right? 391 00:22:08,016 --> 00:22:09,742 And the baby can't stop feeding its brain. 392 00:22:09,776 --> 00:22:12,123 The brain doesn't hold onto energy. 393 00:22:12,158 --> 00:22:15,472 It's a constant, thirsty, demanding organ. 394 00:22:15,506 --> 00:22:19,959 And fat ensures that we always have energy available 395 00:22:19,993 --> 00:22:22,479 to pay for this thirsty organ. 396 00:22:24,412 --> 00:22:27,276 So, when you see a fat, pudgy baby, that's a healthy baby. 397 00:22:27,311 --> 00:22:29,658 Because fat is life, right? 398 00:22:29,693 --> 00:22:32,143 If you don't have enough fat, you're at risk. 399 00:22:36,527 --> 00:22:39,806 As we get older, fat plays a role again, 400 00:22:39,841 --> 00:22:41,532 because you need a sufficient amount of fat 401 00:22:41,567 --> 00:22:43,741 to have enough estrogen... fat produces estrogen. 402 00:22:43,776 --> 00:22:48,021 In fact, girls have to gain on average about 13 pounds or so 403 00:22:48,056 --> 00:22:51,611 before they're able to initiate puberty. 404 00:22:54,373 --> 00:22:58,860 Model Hartje Andresen never thought much about fat 405 00:22:58,894 --> 00:23:01,966 until she confronted the pressure to be thin. 406 00:23:02,001 --> 00:23:04,659 Will you send me the picture? 407 00:23:04,693 --> 00:23:08,283 The photographer who discovered me said, 408 00:23:08,317 --> 00:23:09,318 "You know, you're perfect, 409 00:23:09,353 --> 00:23:10,906 "you're beautiful the way you are. 410 00:23:10,941 --> 00:23:13,322 "But if you get into the modeling industry, 411 00:23:13,357 --> 00:23:15,463 "they are going to tell you to lose weight. 412 00:23:15,497 --> 00:23:18,604 So, my word of advice to you is don't, don't do it." 413 00:23:20,916 --> 00:23:24,886 But for many models, like Robyn Lawley, 414 00:23:24,920 --> 00:23:27,544 that advice was hard to heed. 415 00:23:27,578 --> 00:23:30,063 Women who walked the runway 416 00:23:30,098 --> 00:23:33,481 had to wear size two or smaller clothing. 417 00:23:36,656 --> 00:23:38,624 It was that heroin chic look at the time. 418 00:23:38,658 --> 00:23:41,627 So, it would be, girls of my height, like six foot, 419 00:23:41,661 --> 00:23:43,594 in a size zero. 420 00:23:43,629 --> 00:23:46,735 So, you had to be emaciated to get that look. 421 00:23:46,770 --> 00:23:48,737 You literally had to starve yourself. 422 00:23:48,772 --> 00:23:52,396 And if you didn't do what you were told, you could be cut. 423 00:23:52,431 --> 00:23:54,881 So, I tried, I lost a bunch of weight, 424 00:23:54,916 --> 00:23:57,021 maintained it all for two minutes, 425 00:23:57,056 --> 00:23:58,437 and then it all came back on again. 426 00:24:00,680 --> 00:24:04,097 Hartje lost the weight an agency had requested, 427 00:24:04,132 --> 00:24:07,066 getting down to 100 pounds. 428 00:24:09,517 --> 00:24:12,105 But slowly, she began to realize 429 00:24:12,140 --> 00:24:15,626 that being thin was not necessarily healthy. 430 00:24:18,422 --> 00:24:21,218 My hair had really bad quality 431 00:24:21,252 --> 00:24:23,565 and my fingernails were really brittle. 432 00:24:23,600 --> 00:24:28,812 I would get cracked lips and sores at the corner of my mouth, 433 00:24:28,846 --> 00:24:31,539 but the point that made me realize 434 00:24:31,573 --> 00:24:33,851 that maybe I was getting too thin 435 00:24:33,886 --> 00:24:35,681 was when I started breaking my ribs. 436 00:24:37,993 --> 00:24:40,340 Google "starvation," and that's what happens. 437 00:24:40,375 --> 00:24:42,273 Like, you will lose your period, 438 00:24:42,308 --> 00:24:44,172 you will cause all kinds of diseases 439 00:24:44,206 --> 00:24:47,140 that you never thought would come to you. 440 00:24:47,175 --> 00:24:49,695 When I was speaking to my doctor 441 00:24:49,729 --> 00:24:51,490 about wanting to have a baby, 442 00:24:51,524 --> 00:24:54,389 he actually warned me not to be any thinner. 443 00:24:54,423 --> 00:24:57,668 And even though I was exercising a lot, 444 00:24:57,703 --> 00:25:01,430 I was obviously not healthy. 445 00:25:01,465 --> 00:25:04,019 If you don't have enough fat stores, 446 00:25:04,054 --> 00:25:05,987 one thing that is affected significantly, 447 00:25:06,021 --> 00:25:07,851 is that we develop issues with bone, 448 00:25:07,885 --> 00:25:09,646 which can then lead to osteoporosis... 449 00:25:09,680 --> 00:25:11,026 so, actual brittle bones 450 00:25:11,061 --> 00:25:13,512 that have a high susceptibility to breaking. 451 00:25:13,546 --> 00:25:16,307 And so that's something that people might not think about 452 00:25:16,342 --> 00:25:18,793 as we're looking for this aesthetics 453 00:25:18,827 --> 00:25:23,280 of getting to that Twiggy ideal body image. 454 00:25:27,491 --> 00:25:31,460 At the other end of the scale are sumo wrestlers. 455 00:25:36,155 --> 00:25:40,815 Given their massive size, how do they avoid diseases 456 00:25:40,849 --> 00:25:44,025 normally associated with obesity? 457 00:25:47,960 --> 00:25:51,446 The answer lies in where they store their fat... 458 00:25:51,480 --> 00:25:54,035 safely underneath their skin, 459 00:25:54,069 --> 00:25:56,589 instead of in the abdomen or chest, 460 00:25:56,624 --> 00:26:01,594 packed around internal organs. 461 00:26:01,629 --> 00:26:03,320 And so if you do a scan of an active sumo wrestler, 462 00:26:03,354 --> 00:26:06,910 a CT scan or an MRI scan, you'll see all that fat, 463 00:26:06,944 --> 00:26:09,671 but it's on the outside, it's on the buttocks and thighs, 464 00:26:09,706 --> 00:26:12,571 it's on the outside of the abdomen. 465 00:26:12,605 --> 00:26:16,091 So even though they have body fat, 466 00:26:16,126 --> 00:26:19,094 they don't contain a lot of fat 467 00:26:19,129 --> 00:26:22,132 in those deleterious places such as the liver, 468 00:26:22,166 --> 00:26:25,204 around the heart, around the pancreas, 469 00:26:25,238 --> 00:26:26,481 and even around the kidneys. 470 00:26:26,515 --> 00:26:29,208 So, they're metabolically healthy. 471 00:26:29,242 --> 00:26:34,316 And the key reason is that sumo wrestlers exercise rigorously, 472 00:26:34,351 --> 00:26:36,698 up to seven hours a day. 473 00:26:39,494 --> 00:26:41,116 When we exercise, 474 00:26:41,151 --> 00:26:43,947 our fat releases a hormone called adiponectin, 475 00:26:43,981 --> 00:26:47,053 and adiponectin actually helps guide fats in the blood 476 00:26:47,088 --> 00:26:48,952 into safe deposits of fat, 477 00:26:48,986 --> 00:26:51,195 so they'll guide it into subcutaneous fat, 478 00:26:51,230 --> 00:26:53,473 right under the skin. 479 00:26:53,508 --> 00:26:55,096 Interestingly, 480 00:26:55,130 --> 00:26:58,237 when sumo wrestlers come off their exercise regime, 481 00:26:58,271 --> 00:27:00,791 they get metabolically unhealthy very quickly. 482 00:27:03,587 --> 00:27:05,934 To maintain a stable weight, 483 00:27:05,969 --> 00:27:09,110 the number of calories you eat 484 00:27:09,144 --> 00:27:12,631 needs to match the number you burn. 485 00:27:12,665 --> 00:27:15,012 So many assume that losing weight 486 00:27:15,047 --> 00:27:17,532 is simply a matter of eating less 487 00:27:17,566 --> 00:27:20,915 and exercising more. 488 00:27:20,949 --> 00:27:26,230 But scientists are discovering that it's not so simple. 489 00:27:26,265 --> 00:27:28,198 So, what is astonishing is the fact 490 00:27:28,232 --> 00:27:30,994 that we ingest more than a million calories a year. 491 00:27:31,028 --> 00:27:33,928 And yet we don't oscillate between supermodel 492 00:27:33,962 --> 00:27:36,724 and an opera diva over the whole period of a year. 493 00:27:36,758 --> 00:27:39,727 We stay pretty stable. 494 00:27:39,761 --> 00:27:41,349 So I think the best way to think about how weight is regulated 495 00:27:41,383 --> 00:27:42,937 is to think of it as a set point, right? 496 00:27:42,971 --> 00:27:45,180 That is, that our body is defending 497 00:27:45,215 --> 00:27:49,150 a very particular weight under a certain set of circumstances. 498 00:27:49,184 --> 00:27:52,049 And it's obviously not set 499 00:27:52,084 --> 00:27:54,051 because the body weight can change. 500 00:27:54,086 --> 00:27:56,019 What is set is what is 501 00:27:56,053 --> 00:28:00,644 the minimum body weight for that individual. 502 00:28:00,679 --> 00:28:04,027 If you drop your body weight below this threshold, 503 00:28:04,061 --> 00:28:07,651 the body will begin to do whatever it has to do 504 00:28:07,686 --> 00:28:09,722 to prevent your dying of starvation. 505 00:28:13,277 --> 00:28:14,554 But few Americans grasped 506 00:28:14,589 --> 00:28:17,488 just how hard the body fought against weight loss 507 00:28:17,523 --> 00:28:21,561 until a reality TV show called "The Biggest Loser" 508 00:28:21,596 --> 00:28:23,563 captivated audiences. 509 00:28:23,598 --> 00:28:25,186 Yeah, I made it! 510 00:28:25,220 --> 00:28:28,499 One of the heaviest contestants on season eight 511 00:28:28,534 --> 00:28:30,260 was Danny Cahill. 512 00:28:30,294 --> 00:28:31,192 Yeah! 513 00:28:33,366 --> 00:28:34,609 For Danny, 514 00:28:34,643 --> 00:28:38,613 competing on the show was a shot at salvation, 515 00:28:38,647 --> 00:28:41,581 something he had longed for since childhood. 516 00:28:43,860 --> 00:28:45,447 When I was a kid I was like, 517 00:28:45,482 --> 00:28:48,036 if you could have one wish, what would you wish for? 518 00:28:48,071 --> 00:28:49,935 And you know, most people say, "A million dollars," 519 00:28:49,969 --> 00:28:51,177 you know, or-or something. 520 00:28:51,212 --> 00:28:52,834 I'd say, "I wish I could be like that person 521 00:28:52,869 --> 00:28:58,460 that eats the same as me and seems to never gain weight." 522 00:28:58,495 --> 00:29:01,774 As a child, Danny tended to be heavy, 523 00:29:01,809 --> 00:29:07,607 but by the time he was a father, he struggled with obesity. 524 00:29:07,642 --> 00:29:11,266 His doctor warned that unless he slimmed down, 525 00:29:11,301 --> 00:29:16,306 he might not live to see his kids grow up. 526 00:29:16,340 --> 00:29:18,204 I was mortified at how big I'd gotten. 527 00:29:18,239 --> 00:29:20,344 And it seemed like it happened overnight. 528 00:29:20,379 --> 00:29:22,277 It just sneaks up on you. 529 00:29:22,312 --> 00:29:23,969 You don't feel the pain. 530 00:29:24,003 --> 00:29:25,418 So, when you gain a half a pound 531 00:29:25,453 --> 00:29:28,421 and a half a pound and a half a pound every week, 532 00:29:28,456 --> 00:29:31,148 well, in a year that's 30, 40 pounds. 533 00:29:31,183 --> 00:29:34,186 And in five years, it's a 150 pounds. 534 00:29:37,292 --> 00:29:40,226 Danny saw "The Biggest Loser" as a second chance. 535 00:29:42,194 --> 00:29:44,368 Look at that word, "Believe," okay? 536 00:29:44,403 --> 00:29:48,062 Cutting calories and exercising around 45 hours each week, 537 00:29:48,096 --> 00:29:50,340 he hoped to shed a pound a day. 538 00:29:50,374 --> 00:29:51,341 Let's go. 539 00:29:51,375 --> 00:29:53,136 Top it. 540 00:29:53,170 --> 00:29:54,137 I went there with a purpose. 541 00:29:54,171 --> 00:29:55,621 I went there to lose the weight. 542 00:29:55,655 --> 00:29:57,588 I went there to break a record. 543 00:29:57,623 --> 00:29:59,211 I went there to-to right my life 544 00:29:59,245 --> 00:30:01,938 and to get the weight that I've been carrying around for years 545 00:30:01,972 --> 00:30:03,215 off of me. 546 00:30:05,458 --> 00:30:08,876 As the season progressed, Danny pushed harder, 547 00:30:08,910 --> 00:30:12,811 cutting back to 800 calories a day. 548 00:30:12,845 --> 00:30:16,435 Seven months later, when he stepped on the scale 549 00:30:16,469 --> 00:30:18,161 for the final weigh-in, 550 00:30:18,195 --> 00:30:22,821 he had lost a staggering 239 pounds. 551 00:30:25,513 --> 00:30:28,792 I was mentally exhausted, I was physically exhausted. 552 00:30:28,827 --> 00:30:32,071 In fact, looking back at it, I go, "How did I do that? 553 00:30:32,106 --> 00:30:33,072 "How did we do that? 554 00:30:33,107 --> 00:30:34,384 That is crazy." 555 00:30:36,731 --> 00:30:41,701 Danny was determined to keep the weight off at home. 556 00:30:41,736 --> 00:30:43,531 He delayed returning to work 557 00:30:43,565 --> 00:30:46,223 so he could exercise several hours a day. 558 00:30:48,225 --> 00:30:49,986 When his book tour ended, 559 00:30:50,020 --> 00:30:54,507 he went back to his job surveying land. 560 00:30:54,542 --> 00:30:57,821 Moving less and feeling constantly hungry, 561 00:30:57,856 --> 00:31:01,342 the weight came back. 562 00:31:06,140 --> 00:31:11,904 Danny regained over 100 pounds, and he was not alone. 563 00:31:11,939 --> 00:31:16,667 Six years later, N.I.H. scientist Kevin Hall found 564 00:31:16,702 --> 00:31:21,293 that 13 of the 14 contestants he examined 565 00:31:21,327 --> 00:31:23,571 had regained much of their lost weight 566 00:31:23,605 --> 00:31:25,780 or were even heavier. 567 00:31:28,196 --> 00:31:29,611 When you make extreme changes 568 00:31:29,646 --> 00:31:32,200 to your diet or physical activity patterns, 569 00:31:32,235 --> 00:31:34,858 your body responds very strongly, 570 00:31:34,893 --> 00:31:37,343 both in terms of slowing down the number of calories 571 00:31:37,378 --> 00:31:39,104 that you're burning, as well as 572 00:31:39,138 --> 00:31:41,106 increasing your appetite and hunger. 573 00:31:41,140 --> 00:31:45,213 And those types of processes that are biological, 574 00:31:45,248 --> 00:31:47,215 are well beyond willpower. 575 00:31:47,250 --> 00:31:50,149 Close the door. 576 00:31:50,184 --> 00:31:54,084 Research has revealed that as dieters lose fat, 577 00:31:54,119 --> 00:31:58,088 leptin levels fall, triggering hunger. 578 00:31:58,123 --> 00:31:59,883 In. 579 00:31:59,918 --> 00:32:00,953 Out. 580 00:32:00,988 --> 00:32:02,472 As Danny regained weight, 581 00:32:02,506 --> 00:32:05,026 his leptin levels should have rebounded. 582 00:32:05,061 --> 00:32:06,441 But did they? 583 00:32:06,476 --> 00:32:07,718 You started out kind of 584 00:32:07,753 --> 00:32:09,375 more or less where you would expect 585 00:32:09,410 --> 00:32:11,757 for your amount of body fat. 586 00:32:11,791 --> 00:32:13,103 But six years after "The Biggest Loser," 587 00:32:13,138 --> 00:32:14,553 here's where you ended up. 588 00:32:14,587 --> 00:32:16,244 And I was told that that would tell your body 589 00:32:16,279 --> 00:32:19,109 that you're starving and that you needed to eat. 590 00:32:19,144 --> 00:32:21,422 So, how am I going to handle this, 591 00:32:21,456 --> 00:32:24,287 being hungry all the time with my hormone levels out of whack, 592 00:32:24,321 --> 00:32:27,911 and is that ever going to correct itself? 593 00:32:27,946 --> 00:32:31,087 Thyroid hormones also fell. 594 00:32:31,121 --> 00:32:32,778 And that's one reason 595 00:32:32,812 --> 00:32:35,677 as contestants shed pounds, their metabolic rate... 596 00:32:35,712 --> 00:32:40,130 the number of calories they burn while resting... dropped. 597 00:32:41,856 --> 00:32:43,513 What was the surprise 598 00:32:43,547 --> 00:32:45,135 was that six years later, 599 00:32:45,170 --> 00:32:47,517 their metabolic rate was still at the same level 600 00:32:47,551 --> 00:32:52,004 despite regaining all that body weight. 601 00:32:52,039 --> 00:32:54,179 You started off at zero, basically... 602 00:32:54,213 --> 00:32:56,353 And compared to other contestants, 603 00:32:56,388 --> 00:32:58,700 after Danny's weight rebounded, 604 00:32:58,735 --> 00:33:02,014 his metabolic rate had fallen the furthest. 605 00:33:02,049 --> 00:33:05,638 Your metabolism was about 800 calories a day lower 606 00:33:05,673 --> 00:33:06,777 than what we would expect. 607 00:33:06,812 --> 00:33:08,055 I was shocked. 608 00:33:08,089 --> 00:33:12,887 My body burned 800 calories less than a normal man 609 00:33:12,921 --> 00:33:14,923 that was the same height and weight. 610 00:33:14,958 --> 00:33:16,856 And I just want people to realize 611 00:33:16,891 --> 00:33:21,068 that obese people aren't just lazy people. 612 00:33:21,102 --> 00:33:23,104 There are a whole lot of things at play here, 613 00:33:23,139 --> 00:33:24,726 and one of them is our biology. 614 00:33:24,761 --> 00:33:28,730 So the vast majority of humans fail on a diet. 615 00:33:28,765 --> 00:33:30,318 And, from an evolutionary perspective, 616 00:33:30,353 --> 00:33:33,735 that makes sense because we never evolved to lose weight. 617 00:33:33,770 --> 00:33:35,289 As soon as you go on a diet, 618 00:33:35,323 --> 00:33:37,739 that activates what's called a starvation response 619 00:33:37,774 --> 00:33:40,259 to help us hold onto energy. 620 00:33:40,294 --> 00:33:43,642 The brain remembers that set point. 621 00:33:43,676 --> 00:33:46,231 The brain is a powerful organ. 622 00:33:46,265 --> 00:33:49,786 And the hypothalamus is powerful in knowing what our weight was. 623 00:33:49,820 --> 00:33:53,169 And so the brain wins. 624 00:33:56,172 --> 00:33:57,725 There's another reason 625 00:33:57,759 --> 00:34:03,144 why it's hard to voluntarily control your weight. 626 00:34:03,179 --> 00:34:07,942 It's obvious when looking at identical twins, 627 00:34:07,976 --> 00:34:09,599 that the shape and size of their bodies... 628 00:34:09,633 --> 00:34:14,811 and even their gestures... are remarkably similar. 629 00:34:14,845 --> 00:34:19,229 That's because they share 100% of their genes. 630 00:34:22,267 --> 00:34:24,441 But that's not true for fraternal twins. 631 00:34:24,476 --> 00:34:26,064 They can differ in gender and size, 632 00:34:26,098 --> 00:34:31,172 because they only share half of their genes. 633 00:34:31,207 --> 00:34:34,002 So if you systematically compare 634 00:34:34,037 --> 00:34:35,728 identical to non-identical twins, 635 00:34:35,763 --> 00:34:37,040 what you conclude is that 636 00:34:37,075 --> 00:34:40,388 obesity is as or more genetic than any trait 637 00:34:40,423 --> 00:34:42,390 that's been studied with the exception of height. 638 00:34:44,289 --> 00:34:45,773 These twin studies have shown 639 00:34:45,807 --> 00:34:51,123 that the heritability of obesity is around 40% to 70%. 640 00:34:51,158 --> 00:34:54,195 So, obesity is not just about the environment, 641 00:34:54,230 --> 00:34:56,818 not just about your lifestyle. 642 00:34:56,853 --> 00:34:58,855 Your genetics determine 643 00:34:58,889 --> 00:35:02,307 why some people gain weight more easily than others. 644 00:35:02,341 --> 00:35:04,102 Jump! 645 00:35:07,691 --> 00:35:10,211 To find genes that influence obesity, 646 00:35:10,246 --> 00:35:13,387 a global consortium is analyzing genomes 647 00:35:13,421 --> 00:35:16,044 at centers like the Broad Institute. 648 00:35:17,874 --> 00:35:20,877 Over 1,000 genes have been identified 649 00:35:20,911 --> 00:35:24,467 that may play a role in determining weight. 650 00:35:24,501 --> 00:35:29,127 Most are for common obesity and have small effects. 651 00:35:29,161 --> 00:35:31,577 But not all. 652 00:35:33,200 --> 00:35:36,479 The data, mapped to 23 chromosomes, 653 00:35:36,513 --> 00:35:42,036 is publicly available to scientists like Ruth Loos. 654 00:35:42,070 --> 00:35:45,315 As she homes in on a specific location, 655 00:35:45,350 --> 00:35:50,251 she can search for individual genes. 656 00:35:50,286 --> 00:35:53,427 To date, researchers have identified eight different genes 657 00:35:53,461 --> 00:35:57,465 which can cause severe early-onset obesity. 658 00:35:59,985 --> 00:36:02,884 And most of these genes, they act in the brain. 659 00:36:02,919 --> 00:36:06,198 They control food intake, they control hunger, 660 00:36:06,233 --> 00:36:08,304 satiety, reward... 661 00:36:08,338 --> 00:36:10,616 basically components that we can think of 662 00:36:10,651 --> 00:36:14,344 as controlling willpower. 663 00:36:14,379 --> 00:36:16,726 And there are other gene variants 664 00:36:16,760 --> 00:36:21,731 that don't cause obesity but may make carriers heavier. 665 00:36:21,765 --> 00:36:25,873 One impacts leptin signaling. 666 00:36:25,907 --> 00:36:27,530 If you carry that mutation, 667 00:36:27,564 --> 00:36:30,395 then you would weigh about 15 pounds more 668 00:36:30,429 --> 00:36:32,638 than someone who does not. 669 00:36:32,673 --> 00:36:34,675 And we see that one in 5,000 individuals 670 00:36:34,709 --> 00:36:37,471 in the general population carries that mutation. 671 00:36:39,266 --> 00:36:42,717 But while genes can increase your risk for gaining weight, 672 00:36:42,752 --> 00:36:46,065 they can also protect you. 673 00:36:46,100 --> 00:36:50,069 One gene variant, found in about six percent of the population, 674 00:36:50,104 --> 00:36:55,143 makes carriers always feel full instead of hungry. 675 00:36:55,178 --> 00:36:58,423 Now this variant doesn't make you fat. 676 00:36:58,457 --> 00:37:01,253 It predisposes to making you leaner. 677 00:37:01,288 --> 00:37:03,324 So, we need to understand that there are people 678 00:37:03,359 --> 00:37:06,983 who are very susceptible and people who are very resistant, 679 00:37:07,017 --> 00:37:09,606 that obese people are not morally inferior, 680 00:37:09,641 --> 00:37:11,332 they're biologically different. 681 00:37:13,921 --> 00:37:18,270 Obesity is defined by your body mass index, or BMI, 682 00:37:18,305 --> 00:37:24,000 a calculation that divides your weight by your height squared. 683 00:37:24,034 --> 00:37:28,487 A BMI above 25 is classified as overweight, 684 00:37:28,522 --> 00:37:32,111 and higher than 30 as obesity. 685 00:37:34,148 --> 00:37:39,533 In the 1980s, obesity rates in the U.S. began rising sharply, 686 00:37:39,567 --> 00:37:45,366 reaching higher than 39% in many states. 687 00:37:45,401 --> 00:37:46,712 Obesity by far 688 00:37:46,747 --> 00:37:50,129 is the greatest public health challenge of our time. 689 00:37:50,164 --> 00:37:52,615 It is the number-one chronic disease 690 00:37:52,649 --> 00:37:55,031 that we're dealing with here in the United States. 691 00:37:55,065 --> 00:37:56,584 And it's leading to at least 692 00:37:56,619 --> 00:37:59,898 a hundred different disease entities that we know of. 693 00:37:59,932 --> 00:38:01,555 So we will never 694 00:38:01,589 --> 00:38:03,453 get ahead of diabetes, 695 00:38:03,488 --> 00:38:06,042 we'll never get ahead of cardiovascular disease, 696 00:38:06,076 --> 00:38:08,286 we'll never get ahead of cancer 697 00:38:08,320 --> 00:38:10,495 unless we address the root cause. 698 00:38:10,529 --> 00:38:14,499 And the root cause is, in many cases, obesity. 699 00:38:16,742 --> 00:38:21,264 And it's not just a U.S. epidemic. 700 00:38:21,299 --> 00:38:25,993 In just three decades, obesity nearly tripled worldwide. 701 00:38:27,650 --> 00:38:30,342 According to the World Health Organization, 702 00:38:30,377 --> 00:38:34,346 one problem might be a decrease in physical activity, 703 00:38:34,381 --> 00:38:37,211 causing us to burn fewer calories. 704 00:38:39,351 --> 00:38:43,355 So is one solution to simply be more active? 705 00:38:50,362 --> 00:38:54,262 Back in Tanzania, Herman Pontzer and Brian Wood, 706 00:38:54,297 --> 00:38:57,265 working with a team of international scientists, 707 00:38:57,300 --> 00:39:00,579 hope to find out. 708 00:39:00,614 --> 00:39:05,308 They're giving members of the Hadza community GPS devices 709 00:39:05,343 --> 00:39:09,036 to measure how far they travel each day. 710 00:39:10,796 --> 00:39:11,866 GPS. 711 00:39:11,901 --> 00:39:13,661 The answer might shed light 712 00:39:13,696 --> 00:39:16,284 on why the Hadza don't suffer 713 00:39:16,319 --> 00:39:18,873 from the chronic diseases seen in the West. 714 00:39:20,496 --> 00:39:22,360 Without antibiotics and vaccines, sadly 715 00:39:22,394 --> 00:39:25,293 a lot of kids, you know, don't make it to their 15th birthday. 716 00:39:25,328 --> 00:39:28,814 But if you make it to 15 in the Hadza population, 717 00:39:28,849 --> 00:39:31,369 there's a great chance you're going to live to be in your 60s, 718 00:39:31,403 --> 00:39:32,853 even 70s and 80s, 719 00:39:32,887 --> 00:39:34,751 and with a much healthier body 720 00:39:34,786 --> 00:39:36,960 than we would often have in the West. 721 00:39:39,100 --> 00:39:43,277 GPS data reveals why. 722 00:39:43,311 --> 00:39:48,144 Hunters, like Dofu, walk about nine miles a day, 723 00:39:48,178 --> 00:39:51,872 while women foragers walk about five. 724 00:39:51,906 --> 00:39:58,775 That's more exercise than the average American gets in a week. 725 00:39:58,810 --> 00:40:03,401 But do the Hadza people also burn more calories each day? 726 00:40:05,126 --> 00:40:07,439 I had spent many months living with the Hadza. 727 00:40:07,474 --> 00:40:09,717 I had gone with them during the day of foraging 728 00:40:09,752 --> 00:40:13,583 and come back to camp, and I felt so tired and exhausted. 729 00:40:13,618 --> 00:40:16,586 I felt of course the energy use that we would be detecting 730 00:40:16,621 --> 00:40:19,382 would be much higher than in Western populations. 731 00:40:22,765 --> 00:40:26,872 To find out, volunteers like Dofu drink a special water 732 00:40:26,907 --> 00:40:30,393 with hydrogen and oxygen molecules that can be traced. 733 00:40:30,428 --> 00:40:31,877 Uh-huh. 734 00:40:31,912 --> 00:40:36,813 Over the next two weeks, 735 00:40:36,848 --> 00:40:39,782 by tracking the depletion of these molecules, 736 00:40:39,816 --> 00:40:41,300 the scientists can measure the number of calories 737 00:40:41,335 --> 00:40:43,475 burned each day. 738 00:40:43,510 --> 00:40:46,202 So we've come out here, we collect all this data, 739 00:40:46,236 --> 00:40:49,723 you know, putting urine samples on liquid nitrogen, 740 00:40:49,757 --> 00:40:51,794 shipping them to one of the best labs in the country. 741 00:40:51,828 --> 00:40:53,589 And as the results came back, 742 00:40:53,623 --> 00:40:54,590 I wasn't sure what I was seeing at first. 743 00:40:54,624 --> 00:40:57,040 It's, uh, 77. 744 00:40:57,075 --> 00:40:59,387 Despite being more active, 745 00:40:59,422 --> 00:41:04,531 Hadza men only burn, on average, 2,500 calories per day, 746 00:41:04,565 --> 00:41:08,604 and Hadza women about 1,900, 747 00:41:08,638 --> 00:41:14,230 the same amount as an average man and woman in the U.S. 748 00:41:14,264 --> 00:41:16,508 It's a really counterintuitive result, 749 00:41:16,543 --> 00:41:18,061 and it really surprised us. 750 00:41:18,096 --> 00:41:22,203 Somebody who is sedentary, working a desk job in the U.S., 751 00:41:22,238 --> 00:41:24,447 is burning the same number of calories 752 00:41:24,482 --> 00:41:26,242 as a Hadza man or woman 753 00:41:26,276 --> 00:41:28,244 who's so much more physically active, 754 00:41:28,278 --> 00:41:30,522 and that's even after you account for things 755 00:41:30,557 --> 00:41:34,699 like body size, body composition, age, 756 00:41:34,733 --> 00:41:38,047 gender, all of those factors. 757 00:41:38,081 --> 00:41:42,534 The research suggests that no matter what our lifestyle is, 758 00:41:42,569 --> 00:41:46,055 our body protects us by keeping the total calories burned 759 00:41:46,089 --> 00:41:50,300 each day within a narrow range. 760 00:41:50,335 --> 00:41:54,408 And that's why, in the long run, 761 00:41:54,442 --> 00:41:59,102 exercise alone won't make you thin. 762 00:41:59,137 --> 00:42:01,139 I think what the Hadza data tell us 763 00:42:01,173 --> 00:42:05,419 is that we can change our lifestyles however we want, 764 00:42:05,453 --> 00:42:07,007 and more activity is always better, 765 00:42:07,041 --> 00:42:08,974 but it's not going to burn more calories, 766 00:42:09,009 --> 00:42:13,565 'cause our bodies adjust to these more-active lifestyles. 767 00:42:13,600 --> 00:42:16,672 The implications are huge. 768 00:42:16,706 --> 00:42:20,054 If obesity is not due to sedentary lifestyles, 769 00:42:20,089 --> 00:42:25,335 it must be caused by eating too many calories. 770 00:42:25,370 --> 00:42:28,718 And according to Daniel Lieberman, 771 00:42:28,753 --> 00:42:32,722 that became possible as humans changed their environment. 772 00:42:32,757 --> 00:42:37,209 So in the last 10,000 years we've transformed 773 00:42:37,244 --> 00:42:39,729 both how we get energy, actually, and how we use energy. 774 00:42:39,764 --> 00:42:42,456 And the first big shift occurred with the origins of agriculture, 775 00:42:42,490 --> 00:42:45,321 when we shifted from simply going out and getting food 776 00:42:45,355 --> 00:42:48,186 out there in nature to growing the food ourselves. 777 00:42:50,360 --> 00:42:54,917 Farming allowed humans to grow carbohydrate-rich foods 778 00:42:54,951 --> 00:42:59,646 like corn, wheat, and rice. 779 00:42:59,680 --> 00:43:01,855 And then we invented machines 780 00:43:01,889 --> 00:43:05,410 and industrialized how we grow food. 781 00:43:05,444 --> 00:43:10,622 We've increased the scale of calories that we produce 782 00:43:10,657 --> 00:43:13,487 by orders of magnitude. 783 00:43:13,521 --> 00:43:16,110 And the result is, for the first time in millions of years, 784 00:43:16,145 --> 00:43:18,216 we have more energy than we know what to do with. 785 00:43:21,012 --> 00:43:25,395 And it's not just an excess of calories. 786 00:43:25,430 --> 00:43:27,535 Scientists suspect that obesity may be caused 787 00:43:27,570 --> 00:43:30,780 by the changing nature of the foods we eat. 788 00:43:32,782 --> 00:43:35,543 More than 50% of calories in the U.S. 789 00:43:35,578 --> 00:43:39,513 are consumed in the form of ultra-processed foods, 790 00:43:39,547 --> 00:43:44,483 low in fiber, but full of fat, sugar, and salt. 791 00:43:44,518 --> 00:43:49,799 Packed with calories, they've been labeled obesogenic. 792 00:43:49,834 --> 00:43:53,009 But do they cause us to overeat? 793 00:43:53,044 --> 00:43:58,532 To find out, Nora Volkow has been scanning the brains 794 00:43:58,566 --> 00:44:01,604 of patients with and without obesity. 795 00:44:03,813 --> 00:44:07,023 To me the most important aspect about obesity 796 00:44:07,058 --> 00:44:09,439 is understanding that 797 00:44:09,474 --> 00:44:12,339 the food itself has made changes in your brain 798 00:44:12,373 --> 00:44:15,204 that are driving your inability to stop eating. 799 00:44:17,724 --> 00:44:19,311 These changes begin 800 00:44:19,346 --> 00:44:22,383 as food activates our brain's reward system, 801 00:44:22,418 --> 00:44:26,042 releasing a feel-good chemical called dopamine. 802 00:44:27,803 --> 00:44:31,669 Through pleasure, dopamine motivates us 803 00:44:31,703 --> 00:44:35,638 to find and eat rewarding foods. 804 00:44:35,673 --> 00:44:39,711 Imaging reveals that high-fat, sugary foods 805 00:44:39,746 --> 00:44:42,024 can overwhelm the brain's reward system, 806 00:44:42,058 --> 00:44:46,580 flooding it with too much dopamine. 807 00:44:46,614 --> 00:44:49,514 Our bodies actually have evolved 808 00:44:49,548 --> 00:44:52,966 to try to maintain a homeostatic state. 809 00:44:53,000 --> 00:44:55,900 And that means that if there's too much stimulation 810 00:44:55,934 --> 00:45:00,628 with dopamine, you start to see that receptors 811 00:45:00,663 --> 00:45:03,079 that are sensitive to dopamine 812 00:45:03,114 --> 00:45:05,081 are down regulated, they decrease. 813 00:45:07,877 --> 00:45:10,052 Volkow found that dopamine receptors, 814 00:45:10,086 --> 00:45:13,296 seen as red in the brains of control subjects, 815 00:45:13,331 --> 00:45:18,025 are reduced in people with obesity. 816 00:45:18,060 --> 00:45:21,132 As dopamine signaling goes down, 817 00:45:21,166 --> 00:45:27,690 our capacity to be able to inhibit desires goes down. 818 00:45:27,725 --> 00:45:30,935 So, I say, "I'm not going to eat the chocolate, 819 00:45:30,969 --> 00:45:33,075 "or I'm not going to eat the donut. 820 00:45:33,109 --> 00:45:35,180 I don't want to eat it." 821 00:45:35,215 --> 00:45:36,630 Can I stop it? 822 00:45:36,664 --> 00:45:41,186 And if those areas of the brain are not functioning properly, 823 00:45:41,221 --> 00:45:46,260 no matter how much you want not to do something, 824 00:45:46,295 --> 00:45:48,331 it's very difficult to carry through. 825 00:45:48,366 --> 00:45:51,852 And this explains why people will tell you, 826 00:45:51,887 --> 00:45:54,717 "I did not want to eat the food. 827 00:45:54,752 --> 00:45:57,651 "I knew I was going to gain the weight. 828 00:45:57,685 --> 00:45:59,791 Yet I could not stop myself." 829 00:46:01,689 --> 00:46:05,659 The truth about fat is complicated. 830 00:46:05,693 --> 00:46:10,112 Evolution has designed powerful hormonal and neural signals 831 00:46:10,146 --> 00:46:14,944 to ensure that we eat and defend our weight. 832 00:46:17,153 --> 00:46:20,674 I think what people really need to understand about obesity 833 00:46:20,708 --> 00:46:22,745 is that it's not your fault. 834 00:46:22,780 --> 00:46:26,645 This is not a matter of your willpower. 835 00:46:26,680 --> 00:46:28,786 This is a disease. 836 00:46:28,820 --> 00:46:30,304 It's a chronic disease. 837 00:46:30,339 --> 00:46:32,410 It's a highly complex disease, 838 00:46:32,444 --> 00:46:34,757 and there are many causes of obesity. 839 00:46:36,724 --> 00:46:42,282 So, can obesity be prevented or treated? 840 00:46:42,316 --> 00:46:43,559 The experts say maybe, 841 00:46:43,593 --> 00:46:48,426 using a long-term approach, focused on health. 842 00:46:48,460 --> 00:46:50,980 I don't want to put you on the next diet. 843 00:46:51,015 --> 00:46:53,845 Diet implies that it's short term. 844 00:46:53,880 --> 00:46:55,882 I want to put you on a lifestyle plan 845 00:46:55,916 --> 00:46:58,436 that you can sustain for years. 846 00:46:58,470 --> 00:47:00,231 In place. 847 00:47:00,265 --> 00:47:04,235 While "The Biggest Loser" reveals why diets fail, 848 00:47:04,269 --> 00:47:07,686 contestants like Danny... who continue to exercise... 849 00:47:07,721 --> 00:47:12,830 kept off ten to 13% of their weight. 850 00:47:12,864 --> 00:47:14,728 And medically, that's a success, 851 00:47:14,762 --> 00:47:18,042 because modest weight loss has huge health benefits, 852 00:47:18,076 --> 00:47:22,874 from lowering blood pressure to preventing diabetes. 853 00:47:22,909 --> 00:47:28,466 There're also medications that signal the brain to feel full, 854 00:47:28,500 --> 00:47:33,678 and help people lose ten percent of their weight. 855 00:47:33,712 --> 00:47:36,888 And if you want to lose 100 pounds or more, 856 00:47:36,923 --> 00:47:39,822 there's another option, 857 00:47:39,857 --> 00:47:44,447 one that Muriel Mena chose to avoid the fate of her mother. 858 00:47:46,622 --> 00:47:50,695 I was three, and I remember she was talking on the phone, 859 00:47:50,729 --> 00:47:55,803 and she collapsed because she had a heart attack. 860 00:47:55,838 --> 00:48:00,256 And then I just remember E.M.T.s rushing in. 861 00:48:00,291 --> 00:48:05,537 At age 44, Muriel's mom weighed 300 pounds 862 00:48:05,572 --> 00:48:08,575 and had died of heart disease. 863 00:48:08,609 --> 00:48:13,752 As an adolescent, Muriel began struggling with her weight, 864 00:48:13,787 --> 00:48:16,755 just as her mother had. 865 00:48:16,790 --> 00:48:19,724 I was going to the doctor's and having to get my heart checked, 866 00:48:19,758 --> 00:48:21,105 and I was like, "Wait, this is weird. 867 00:48:21,139 --> 00:48:23,624 Like, I'm 13 at a cardiologist." 868 00:48:23,659 --> 00:48:25,385 It was always in the back of my mind, 869 00:48:25,419 --> 00:48:29,285 "Oh, this is what she passed from." 870 00:48:29,320 --> 00:48:34,290 By age 16, Muriel, like nearly five million American teenagers, 871 00:48:34,325 --> 00:48:38,260 had obesity, and qualified for bariatric surgery, 872 00:48:38,294 --> 00:48:42,920 which bypasses or removes part of the stomach. 873 00:48:42,954 --> 00:48:47,372 Bariatric surgery is the only way 874 00:48:47,407 --> 00:48:50,893 that most people with severe obesity 875 00:48:50,928 --> 00:48:54,448 can not just lose weight but most importantly keep it off. 876 00:48:57,003 --> 00:48:59,005 So you've been doing great. 877 00:48:59,039 --> 00:49:01,421 The first thing I want to show you is 878 00:49:01,455 --> 00:49:04,113 275 was your highest weight. 879 00:49:04,148 --> 00:49:07,634 Your body mass index was 43. 880 00:49:07,668 --> 00:49:12,363 After surgery you went all the way down to 172 pounds 881 00:49:12,397 --> 00:49:14,192 and a BMI of about 28. 882 00:49:14,227 --> 00:49:17,989 And that's really fantastic. 883 00:49:18,024 --> 00:49:22,683 Originally we thought that bariatric surgery worked 884 00:49:22,718 --> 00:49:25,134 by making the stomach much smaller, 885 00:49:25,169 --> 00:49:27,619 so that you couldn't eat a lot of food. 886 00:49:27,654 --> 00:49:31,278 We now know that the hormones that come from the G.I. tract 887 00:49:31,313 --> 00:49:33,556 and go to the brain change in a way 888 00:49:33,591 --> 00:49:39,355 that cause satiety earlier, sooner, and with much less food. 889 00:49:39,390 --> 00:49:44,602 These signal changes between the gut and brain 890 00:49:44,636 --> 00:49:49,020 help the body reset its set point for years. 891 00:49:49,055 --> 00:49:53,093 But hunger can return, 892 00:49:53,128 --> 00:49:54,853 because our weight is as regulated 893 00:49:54,888 --> 00:49:59,548 as our blood pressure and heartbeat. 894 00:49:59,582 --> 00:50:00,756 The ability to control our weight 895 00:50:00,790 --> 00:50:03,759 is distinctly outside our conscious control. 896 00:50:03,793 --> 00:50:05,450 People don't like to hear that. 897 00:50:05,485 --> 00:50:07,038 We all want to think that we're in control 898 00:50:07,073 --> 00:50:08,936 of when we put the fork down. 899 00:50:08,971 --> 00:50:11,042 But there are lots of biological forces 900 00:50:11,077 --> 00:50:15,253 that are controlling what weight it is that you end up at. 901 00:50:15,288 --> 00:50:17,842 Fat behaves differently on all of us. 902 00:50:17,876 --> 00:50:19,154 It has to do with our genetics. 903 00:50:19,188 --> 00:50:21,501 It has to do with our age, our gender, 904 00:50:21,535 --> 00:50:22,916 a whole host of factors. 905 00:50:22,950 --> 00:50:27,093 Everybody is very different. 906 00:50:27,127 --> 00:50:29,888 And what matters is to be healthy, 907 00:50:29,923 --> 00:50:31,373 not to be perfect. 908 00:50:33,064 --> 00:50:37,586 Today, Hartje Andresen is 20 pounds heavier, 909 00:50:37,620 --> 00:50:40,589 a mother, and modeling on her own terms. 910 00:50:42,556 --> 00:50:45,870 I had to overcome this fear of gaining weight, 911 00:50:45,904 --> 00:50:48,769 and that really took some courage for me. 912 00:50:52,014 --> 00:50:54,051 Modeling has the possibility 913 00:50:54,085 --> 00:50:57,399 to show people how a healthy body should look like. 914 00:51:00,057 --> 00:51:03,370 The focus needs to be more on strength and health 915 00:51:03,405 --> 00:51:06,856 rather than being a certain size. 916 00:51:08,893 --> 00:51:12,345 And there's another insight provided by the Hadza, 917 00:51:12,379 --> 00:51:15,417 and hunters like Dofu. 918 00:51:15,451 --> 00:51:18,696 What the Hadza tell us is that 919 00:51:18,730 --> 00:51:21,630 diet and exercise are two different tools 920 00:51:21,664 --> 00:51:23,114 with two different jobs. 921 00:51:23,149 --> 00:51:25,806 You need to exercise to stay healthy 922 00:51:25,841 --> 00:51:28,050 and to age well, 923 00:51:28,085 --> 00:51:29,638 but you need to watch your diet 924 00:51:29,672 --> 00:51:31,812 if you want to watch your weight. 925 00:51:31,847 --> 00:51:34,160 It's not a coincidence that 926 00:51:34,194 --> 00:51:37,128 the obesity epidemic is spreading around the world. 927 00:51:37,163 --> 00:51:40,614 Wherever modern, Western, post-industrial lifestyles 928 00:51:40,649 --> 00:51:43,479 show up, obesity follows with them. 929 00:51:43,514 --> 00:51:45,723 But I don't think the solution is to go back to the Stone Age. 930 00:51:45,757 --> 00:51:49,278 I think the solution is to learn from our evolutionary history 931 00:51:49,313 --> 00:51:52,385 and get the best of both worlds.