"I just wanted to show you my originally fairly slim abdomen, something like this, and now look at it." "That is disgusting." "It's just filthy." "Thanks to Horizon, they're going to spend four weeks eating more than they've ever done before of all the foods we're always being told to avoid." "Oh, my God!" "This month of gluttony is all to answer a question that science has struggled with for 40 years." "The fight against fat is being lost all over the world." "Britain's children are facing an obesity time bomb." "Obesity is now so rife that it has brought about an evolutionary change in the human body shape." "We're all going to become fat." "Low-besity, that's the new word." "The full extent of Britain's obesity crisis is revealed in a new government report." "Inside this London cafe, of a rapidly disappearing part of the UK population." "Unlike the 15 million of us who are dangerously overweight, these people are all... slim." "The question they're here to help us answer is how they managed to" "stay that way, despite most of them never having dieted in their life." "I've always eaten whatever I want to eat, and my weight's always been stable and I've always been quite slim." "I'm really lucky and my friends hate me." "I'm constantly on a diet." "It's called the "see food" diet." "I see food and I eat it." "I eat a fair amount of food, but my weight stays quite constant, so I thought it would be interesting to participate in this." "So what's their secret?" "The field of obesity research is stuffed full of studies examining those who are already overweight." "But recently, an expanding number of scientists have decided it's time to take a closer look at the skinnier ones amongst us." "I've always been interested in people claiming that they can't get fat even though they eat a lot." "99.9% of studies today on obesity is really made on already obese people, and doesn't really give you any reasons for why people get obese." "We need to figure out some way to avoid obesity, and why not try to learn something from those that apparently can't get obese." "Swedish scientist Professor Fredrik Nystrom has come up with an experiment to investigate how different people's bodies cope when they eat a lot more than they need to." "Over the next four weeks, our brave volunteers will be eating double their normal number of calories and doing no physical exercise." "It's a regime guaranteed to induce significant weight gain in even the slimmest person." "At least that's what you'd assume!" "But 40 years ago, a group of American scientists carried out a little-known study, and their incredible findings suggest otherwise." "Their story begins in the most unlikely of places." "In 1967, the inmates of the Vermont State Prison were approached by medical researcher Ethan Sims to take part in a unique experiment." "He wanted to find out about the hormonal changes in our bodies when we become seriously overweight, and in order to study that, he needed to take a group of people and make them fat, very fat." "The study called for each inmate to gain 25% of their body weight." "In return, they were promised early release from jail." "Over the course of the year the team fed the volunteer prisoners as much as they could physically eat, and carefully monitored their bodily changes, but as it went on," "Dr Sims became concerned by an unexpected finding." "However much they ate, some of the prisoners could not reach the target." "Two of the prisoners got stuck at 21%, and one of them couldn't put any more than 18% extra body weight despite eating as much" "The experiment pointed to a fascinating and unexpected conclusion." "it seemed that for some people, becoming obese is not just unlikely..." "..it's practically impossible." "For years Sims' results remained the subject of fierce debate." "Could it be true that some people really can eat as much as they want without becoming obese?" "And if so, how do they do it?" "Good evening, everyone, and welcome to Horizon's over-feeding experiment." "Before we all get started, we want to show you how much food you are expected to eat for a typical week." "So if you help me to remove these..." "The food on the table corresponds to 35,000 calories which in turn would give you 5,000 calories a day," "That's a lot of food." "I think I might run home." "LAUGHTER" "It's quite scary, it is quite scary." "It's quite shocking, and also the drinks as well with the milk shakes and things like that." "It made me feel sick just looking at it." "It's quite horrifying." "Having seen all the food here today," "I think it's going to be a lot harder than I envisaged before." "Obviously it's a bit daunting, but I reckon it's deceptive." "I reckon if, you know, you spooned it into days rather than just all these plates here, I reckon it would look fine." "I reckon I can take that." "If the Vermont prison experimenters were right, there could be surprising differences in how the bodies of the volunteers respond to their new diet." "Some might fail to put on much weight at all and, at the other end of the scale, there's a chance that someone may have to leave the study before the four weeks is up." "The upper limit of the increase in body weight in this experiment will be 15%." "It's not ethical to go any further than that." "If anybody increases 15%, they're going to be taken out of the study." "The average weight of our volunteers is around 63kg." "An increase in body weight of 15% would mean nearly ten extra kilograms, or one and a half stone." "For the women, this could mean going up two dress sizes in four weeks." "People are quite horrified that a girl's doing it." "They can understand why guys might do it, and sort of get to eat as much as they want, but no-one seems to get why a girl would want to get fat." "During the experiment, we'll keep track of the participants' weight, and carry out a series of medical tests on them." "The aim is to uncover some clues as to how they manage to stay slim in an increasingly fat world." "Not that fat is necessarily a bad thing!" "At least that's what Dr Philipp Scherer believes." "He has devoted to his career to studying this much-maligned substance." "So what we're looking at here is a rather large piece of bovine fat, from a cow, obviously, and if you look at fat tissue from humans, that would look exactly the same way." "So this is the tissue that has a really bad reputation, marvellous substance, wonderful qualities to it." "When it comes to fat, all most of us want to do is get rid of it as quickly as possible." "We don't stop to think about what our fat does for us." "Inside this fat tissue, we've got billions and billions of little fat cells, and each one of these fat cells has an oil droplet stored, and if the body is in need of energy, it can burn this oil in a chemical reaction." "The energy contained inside these cells can keep us going when food supplies are scarce." "Our fat is our body's built-in emergency rations." "There is in fact a pretty wide range within the human population in terms of how much fat each one of us carries around." "There are those that are seriously overweight, and some of those can actually... have up to 100 times the amount of fat that you see in this bowl." "And the more fat we have, the longer we can keep going without eating, as one Scottish PhD student found out." "In 1968, she began conducting an experiment on a 450lb man who was desperate to lose some weight." "He agreed to begin fasting under her medical supervision, and stopped eating or drinking anything but water and vitamins." "Eventually he managed to lose 275 pounds in weight." "He had lasted an incredible year and two weeks without food." "But even a slim person can live off their fat for several weeks." "The average lean individual probably has about ten times the amount of fat that you see in this bowl, and it makes you wonder, where are we putting it all?" "What this means is the average individual can easily keep going for more than a month." "In today's world, of course, we never need to go without food for anything like as long as a month." "In fact, we are unlikely to have to last more than a few hours." "But that wasn't the case for most of human history." "According to obesity geneticist, Dr Eric Ravussin, our hunter-gatherer ancestors had to live off whatever they could find." "Sometimes that wasn't much, which is when fat as an efficient storage system really came into its own." "Populations went through periods of feast and famine." "During the periods of famine, maybe two-thirds or three-quarters of the population would disappear." "But those who were chubbier or those fatter babies would survive and then procreate themselves and pass on these genes." "So according to this theory, at times of famine, it was literally a case of the survival of the fattest." "The cycles of feast and famine that humankind has been subjected to was an important natural selective process in which all the babies or the people who were a little bit chubbier would survive the periods of famine, and then be able to gain the weight during the period of feast." "This could explain why large parts of the population have a tendency to lay down fat stores easily." "It's only very recently in human history that this has become a problem." "Now the feast is constant, you have food available every corner, very cheap, very palatable and this is really a perfect mixture to provide the expression of these genes and confer obesity and weight gain to these people." "And I think that this stigmatising of the obese population is wrong, because those were the survivors, those are the people who would survive a difficult and tough environment." "But although putting on fat easily may have been an advantage in the past, in today's environment, the opposite is true." "It's the naturally slim who live longer, healthier lives." "It's the day before our volunteers begin their four weeks of over-feeding, and they've come to the University of Westminster for some tests." "Every inch of their slim physiques will be scrutinised." "OK, a sharp scratch coming up." "Ania Kosicka will be carrying out the various tests." "And clinical obesity specialist, Dr Carel le Roux is overseeing the experiment." "He will be monitoring the health of the volunteers throughout." "You have not increased much." "It's gone from 48kg to..." "Determining how much body fat they currently have involves the space-age Bodpod..." "BODPOD VOICE:" ""Welcome to the Bodpod."" "..a shower cap..." "Quite how this is going to work, I don't know." "..and no clothes." "What this measurement does is it actually looks at the air that's been displaced by the body." "HE TAKES DEEP BREATH" "And by using the patient's age, gender, as well as weight, we can actually calculate how much of his body is fat and how much of his body is muscle." "OK, so your percentage body fat is 7.6." "Which puts you in the ultra-lean category, OK?" "According to the Bodpod, hospital administrator Leo Dennett has the lowest percentage body fat of all the participants." "And medical students Catherine Hannon and Victoria Pagner have the most." "In both their cases, fat makes up at least 20% of their body." "What we saw today in the volunteers is that the men had half the amount of fat than the women, and that is what we would expect in the general population." "For the purposes of the experiment, each volunteer's normal daily calorie requirement has been calculated taking into account their physiological statistics." "These individual figures have then been doubled to work out how much each of them will be eating over the next four weeks." "They're also banned from doing any physical exercise that could skew the results." "They're also going to carry pedometers so that we can keep track of the amount of steps that they make, and we ask them not to walk more than 5,000 steps a day, which roughly corresponds to something like two miles." "For many of the volunteers, the tension is building as they face up to what lies ahead." "I'm actually very nervous now, because tomorrow morning I've got to eat a huge breakfast, a massive, massive fry-up and, and there's not going to be enough time in the day, I think, to fit in all this eating!" "I was definitely looking at fat people on the tube... with a bit of apprehension, but I'm pretty sure that I doubt that" "I'll go anything above like... ..what, 73, something like that." "I think I've got it under control." "Many of us are concerned by the slightest change when we step on the bathroom scales." "But New Yorker Dr Rudy Leibel is surprised that our weight doesn't fluctuate a lot more." "One of the remarkable aspects of human body weight actually is how stable it is over relatively long periods of time." "So for example the average adult between the ages of 20 and 50 or 60 years of age may gain 20 or 30 pounds." "But when you do the maths on this, it's as little as seven extra calories or ten extra calories of food a day, which works out to a potato chip or a French fry." "It seems that most of us stay the same weight for the whole of our adult lives, apart from a slow middle-aged spread." "But if all that was affecting it was diet, we'd have to be controlling the number of calories we eat to within seven calories a day." "We don't think that a human could consciously control their body weight to that level of precision." "Instead Dr Leibel believes that we all have a biologically-determined natural weight which varies from person to person, and our bodies do their best to maintain us at that weight, be it fat or thin." "That doesn't mean that you cannot, by over-eating consciously or responding to delicious meals that are in the environment, or for example undertaking a conscious effort to exercise a lot, can't move this around a little bit, but the body will constantly tend to" "try to bring you back to whatever your normal body weight is." "So if we're all stuck with a natural weight, what determines it, and how early in life is it set?" "According to Dr David Allison, even events that take place before we are born whilst we are still in the womb can affect the size we are destined to become as adults." "There's now clear and emerging lines of evidence indicating that several factors can have long-term effects on obesity and degree of body fatness" "throughout life, even when those effects occur in the womb." "We know that, for example, older sheeps have fattier lambs, and we know that older women, women who give birth at a later age, tend to have children that are more likely to be overweight or obese." "And it seems that the mother's weight and nutrition during pregnancy are also crucial." "We also know that a mother that is overfed or obese or diabetic at certain portions of the pregnancy will produce offspring that have a greater probability of themselves being overweight or obese." "There are a host of other possible influences including environmental factors, even pollution." "Scientists are only just beginning to uncover the many things that may predetermine our weight." "but the message is clear." "It seems our size is much less under our control than we might believe." "Day one." "I've eaten today two chocolate croissants, a lot of Crunchy Nut and milk, pork pie, a whole pizza with mayonnaise, bottle of smoothie, tub of ice cream, Ben and Jerry's Phish Food," "couple of burgers and some vegetables, um... but I did cheat because I kind of vomited once." "Um...it's pretty difficult." "Felt pretty ill most of the day." "Two pork pies." "Jaffa Cakes." "A large Quarter Pounder Cheese meal with strawberry milk shake and a McFlurry." "Then another pork pie." "A melt-in-the-middle chocolate pudding with cream...ha-ha-ha!" "Chicago Town deep dish pizza which is "made to share", which is probably why it's 1,240 calories." "Pizza with lots of mayonnaise." "Half a cheesecake and a litre of Coke." "A sausage roll has 90% of the calories of a Mars Bar." "A whole tub of Ben and Jerry's with golden syrup." "McDonalds again for breakfast." "Pork pie." "Yeah." "Another pork pie." "Pate and asparagus, in a sort of...melange." "Chocolate pudding with cream, washed down with a litre and a half of Coke." "To be honest I've hardly stopped eating all day." "And I've had some of the kind of most calorific food known to man, and I've been full all day, and I'm still nowhere near my target." "I think I went into this thinking it would be easier than it is, and I felt sick, I feel..." "I feel disgusting." "This lack of exercise is killing me," "I mean, not being able to walk is driving me mad." "I have a kind of a constant sickly sweetness taste in my mouth." "Try and get it off." "I did discover that McDonalds doesn't fill you up at all, it has loads of calories in, which is good." "And beer has a lot of calories in." "I thought Guinness would be a lot, but Guinness is actually less than most lagers, which is surprising." "OK, so this is the end of day six." "Tomorrow is our first weigh-in." "I'm really interested to see how much weight" "I'm going to have put on." "At the week one weigh-ins, there's a surprise in store for one of the participants." "OK, hello, Thomas!" "Hello!" "Thomas?" "Yes." "Your weight last week was 68.3kg." "This week, it's 71.1kg." "So there's about 3kg increase, and your percentage body fat was 14% last week, and this week it's 16.2." "I guess I'm putting the weight on where it matters." "I don't know." "I guess," "I guess I kind of expected that to happen, but not quite as fast." "I'm a bit intrigued about what it's going to be like next week, third week, fourth week, because I can expect it to get worse..." "So...trousers, that's a worry." "I'm a big man for tight trousers." "Must do some shopping." "2.8kg is equivalent to 4.1% of Thomas's original body weight." "It's the highest percentage increase out of the group." "The moment of truth." "In second place is Leo Dennett on 3.2%." "The percentage body fat today is 10.4." "Oh, right." "So we have about 3.2% increase." "OK." "It's quite a lot in one week." "Yeah, I'm not surprised, really, to be honest." "According to the Bodpod, he's gained so much new fat he's moved out of the ultra-lean category whereas both Aisha Rashid and Martin Wong have only gained a paltry 1.6% body weight." "It's almost like a mini-competition." "I'm aiming to either have to get withdrawn from this by putting on so much weight, or turn up on the last day going," ""Yeah, I've been eating loads and I'm still hungry."" "BODPOD: "Welcome to the Bodpod, please open the door." Stylish!" "So, just one week in and already there are striking differences in weight gain amongst the volunteers." "Look at the results..." "Doubling your normal number of calories does not affect everyone in the same way." "So I've put on one kilo, but 5% more fat." "Yes." "But the biggest surprise for many of the volunteers is how hard it has been to eat double their normal number of calories." "It does get really sickening, like waking up at..." "5am to eat chocolate peanuts!" "You start off feeling terrible and can't eat, so you get behind, when you feel terrible and you're behind, you think to feel un-terrible you should force yourself to eat." "Then that makes you feel more terrible, and you end up missing a meal, and end up losing more calories than you made up by forcing the snacks down yourself, and you just feel more terrible, and before you know what's happened," "it's 7pm and you're like...right!" "Eff today, I'm starting again tomorrow." "As their food diaries reveal, our volunteers are all finding it a lot easier to make up their calorie targets using certain foods." "This bottle of Belgian chocolate milk is 500ml and has 620 calories." "Lots of chocolate." "Chocolate mousse." "Chocolate milk pudding." "Chocolate trifle." "Chocolate." "A huge chocolate milkshake with ice cream." "And one of those little Gold chocolate bars." "A marbled Belgian chocolate cake slice, which was 305 calories and quite nice." "Chocolate mousse." "Swiss chocolate Original." "A big chocolate tart." "Belgian chocolate flapjack." "A chocolate muffin." "Mint truffle chocolate bar and a Turkish delight chocolate bar." "And...more chocolate." "It's Saturday night, and I need an extra 1,100 calories." "I found this little bad boy." "A good cake!" "Our volunteers found that eating chocolate was a very good way of increasing the number of calories." "The reason for that is chocolate is very calorie-dense." "That means there's a lot of calories in a small amount of volume, and therefore you can eat the chocolate and actually have another one before you feel full." "That's why chocolate is so dangerous." "But the question is, why are some of us so much better at walking past an open bar of chocolate or packet of biscuits than others?" "Is staying slim simply a matter of exerting a little self-control?" "As a psychologist I've always been very interested in eating behaviour, and specifically the question of why some people seem to eat more than they strictly need to fulfil their energy requirements." "People often assume that the answer to that is just willpower or self-control, but I think there's more to it than that." "Professor Jane Wardle has been investigating why some people persistently eat more than they really need to." "She's come to the Hopes and Dreams Nursery in North London to repeat one of her recent experiments." "The idea of this study is to see how responsive people are, children are in this case, to food that's put in front of them at a time when actually they're fairly full." "The experiment starts after lunch, with colouring." "I'd quite like to check that from their point of view they do feel full." "Empty, half full or full?" "Do you think your tummy's full?" "CHILD:" "I had two." "So they choose which of these figures is how they feel, and I think pretty well all the ones I've heard talking have said they feel very full." "Now they're all being handed a little plate, or quite a big plate actually, of party-type food, and each child's told they can eat the food, or they can colour, or they can do a bit of each as they choose." "Each plate of food contains 340 calories' worth of chocolate, cakes and biscuits, cut into small pieces." "To put this in perspective, that's approximately a quarter of these children's average daily requirement of calories." "If you look round, you can see there's already a lot of difference in what's going on." "You know, that little boy over there, he seems to have pushed his plate right over to the other side of the table." "you know, as though he's not interested at all in it." "But the boy he's sitting next to is kind of eating away." "Now if you look at that table down there, the two children at each end their way through all the food on their plates, and if you look at the two sitting either side there, interested at all." "They're not just all copying each other and doing the same as the other children on the table." "Jane believes that these behaviour patterns are already well-established in these four- and five-year-olds." "For some people, once they feel that they're full, their enthusiasm and interest in doing any more eating is just switched off, whereas others, as long as the food that they're being offered is attractive and good tasting, they're happy to carry on eating." "Studies have shown that our eating behaviours are fixed from a very young age." "The chances are if you have a tendency to carry on snacking after you're full as a toddler, you'll behave the same way as an adult." "The problem is that it's not long before these habits start to affect your body weight." "By age 11, you usually will start seeing there are associations between these kind of traits, and the children's weight." "The interesting question for us now is where the variability that we see in children's eating behaviour comes from." "Is it something that's learned at home in the family context, or is it something that is innate, and perhaps a genetic characteristic?" "So we've been doing a very similar experiment to the one that you saw here, but the children in that study, we've also tested them to see what variant they have on a gene called the FTO gene." "types of the FTO gene." "Adults who have one variant of this gene weigh on average more than everybody else." "And what we showed was that the children who ate more in this so-called eating in the absence of hunger task, tended to have the higher risk variant of the FTO gene, and the children who ate very little" "had what I think of as being the protective variant of the gene." "It seems that the size of our appetite has a genetic basis." "So it looks like that for some people, resisting all the foods that are available in the modern environment is actually fairly easy." "It's kind of effortless because they don't even want to eat them, they're not having to exert willpower and self-control, whereas for other people, their brain responses to foods that they're exposed to aren't being switched off effectively" "as a consequence of them already having had enough." "Hello!" "OK?" "Come through." "Professor Wardle's findings could certainly explain why some of our volunteers started off so slim." "To be honest, I don't really eat when I'm not hungry." "I mean, if I am hungry, I can eat and eat and eat, but as soon as I stop being hungry, I stop eating." "I'm not the kind of person to go for extra biscuits or sugary snacks if I'm not hungry." "I don't normally eat when I'm not hungry," "I don't eat just for the sake of it." "At weddings or things when we've had a huge amount of meal, and then they bring out the desserts and they look really pretty, and I would go for one, just impulsively, and I'd have a spoonful or something," "but then I just couldn't eat any more." "So I'd really want to, but I wouldn't be able to." "It seems that in everyday life, they're the kind of people who just don't have any desire to eat more than their body needs." "of the experiment, all of our volunteers are ignoring their normal appetites." "And now I'm about to tuck into this, admittedly a meal meant for two people, but obviously for the purpose of this experiment," "I shall be eating it all, with my flat-mates very impressed with that." "1,700 calories, that's more than a fry-up... that I had this morning." "They have to eat their calorie targets, whether they feel like it or not." "And in some cases, that means desperate measures." "What's Tom going to eat?" "Ooh, the...clotted, the clotted cream." "Finished!" "Not really..." "Almost finished." "Hello, Thomas." "At the week two tests, there are still big differences in weight gain between the volunteers." "First week it was 73cm." "Now you're 76.8." "Nearly 4cm in two weeks!" "Six centimetres!" "Six centimetres in two weeks." "I probably did have tight trousers then!" "Thomas Hampton and Thomas Patel-Campbell are now both more than 6% heavier than they were at the start." "But Martin Wong has put on only 3.5% in weight, despite sticking to his calorie target," "There has to be another explanation." "The key issue are where the calories end up." "If it doesn't end up as fat tissue," "I mean, those that apparently have more difficulties in gaining weight than others, somehow they have to spend the calories." "Different groups of scientists have different theories to explain how people's bodies use up excess calories if they're not storing them as fat." "We'll be putting one of these ideas to the test." "In this study we are interested in what is really the essence of being protected against becoming obese, and a theory we have is that the people who can eat a lot and not putting on any weight actually increase the basal metabolic rate," "which is proof that they make heat out of the calories they consume rather than putting it on as fat tissue or exercise, either way." "Our base, or resting, metabolic rate is a measure of how many calories our body uses just keeping us alive." "It's the amount of energy our body needs to keep our heart beating and our brain whirring." "Our volunteers are having their resting metabolic rate tested at regular intervals throughout the experiment." "At the end of the four weeks, these measurements may help to explain why some people have stayed skinnier than others." "But even the slimmest members of our group shouldn't assume they'll stay that way for ever." "Dr Nikhil Dhurandhar believes that there is something out there that could turn even a naturally thin person fat." "He believes that obesity may be catching." "My studies with obesity began in the late-80s when a colleague of mine was investigating a viral infection in chickens which was killing chickens by the thousand." "What was odd about the phenomenon was that these chickens had a lot of fat." "When Dr Dhurandhar's team tried infecting another group of chickens with this SMAM-1 virus, they too became ill and fat, but what they didn't know was whether this chicken virus had crossed over into the human population, and whether it could make us fat too." "Experiments with animals are in one sense simple, because you can take an animal, infect it with a virus and see a cause and effect." "Of course, for ethical reasons, you can't do this with humans." "You can't take humans, even if they are willing, you can't infect them with a virus to show a cause-and-effect relationship." "So instead, Dr Dhurandhar took blood samples from 50 of the overweight patients that he was treating at his obesity clinic." "His team analysed their blood, looking for the presence of antibodies to the chicken virus which would show that they had been naturally infected at some point in their lives." "Turns out about 20% of them were infected with the virus, and as we predicted, these naturally infected people were significantly heavier compared to their antibody-negative counterparts." "Since then, Dr Dhurandhar's team have begun studying a human pathogen which belongs to the same family of oedemal viruses as the chicken virus." "In humans these oedemal viruses cause cold and cough, or pink-eye - conjunctivitis - or diarrhoea, and we have now more than a thousand patients studied, and it continues to show association with obesity and this infection with this virus." "In one study, Dhurandhar's team found that obese people were nearly three times more likely to have the virus than a non-obese person, and, even amongst the non-obese group, those infected with the virus were heavier than average." "And when they started studying how the virus spread through the body, they found out why." "From our animal studies, we now know that this virus goes to the lungs and spreads through the body, goes to various organs and tissues, goes to the liver, kidneys, the brain and fat tissue." "When this virus goes to this fat tissue, it replicates, making more copies of itself, and in the process, increases the number of fat cells." "Which may explain why the fat tissue expands, and why people get fat when they are infected with this virus." "Should we be avoiding fat people?" "Are they going to make us fat too?" "I am often asked this question, but based on our animal studies, we believe that people would be infectious only for a short period of time, maybe two or three months after they are infected." "That's one." "But the other thing is people could be fat for reasons other than viral infections, so it's really pointless to try to avoid fat people to prevent infection." "Dr Dhurandhar's research suggests that even the volunteers who put on the least weight in our experiment shouldn't feel too complacent." "The next cold they catch could come with some undesirable side-effects." "Look at my tummy." "Look at that, it's just it's not normal to me at all, and it's really uncomfortable." "My jeans are too tight, and I'm sick of it." "I can't wait to get rid of it all." "During the last two weeks of the experiment, many of our volunteers are starting to really notice the changes taking place in their body for the first time." "This is insane." "I've had to go up two dress sizes, and I've actually gone up two cup sizes on my bra as well." "My trousers are tighter." "My jeans don't fit me and I've got the muffin-top, with love handles round the sides." "Everything's a bit flabbier." "I have felt that I've got a bit more of a gut." "You've got a bit of a belly." "A little bit, yeah." "It's just a kind of, I don't know, it doesn't usually bounce that much." "I haven't exactly been playing with it or anything, but it's kind of..." "Most of us never think about what's actually going on under our skin when we start gaining inches." "But not everybody's fat is the same, and that's one reason why some of us are bigger than others." "It was in the early-60s that people for the first time started to ask the question, what happens when you gain weight with respect to our fat cells?" "Obviously you have two possibilities." "They can either increase in size, or they can increase in number, and the fact is both of these things happen." "So if we start out with a set of small fat cells that we see here, and we start to over-eat, these fat cells tend to get bigger and they start to accumulate more energy, more oil and eventually they turn into these huge cells" "that you essentially can see with your naked eye, the size of a full stop." "It's what happens next that decides whether you will spend the rest of your days fighting the flab." "This increase in fat cell size happens up to a certain point beyond which these cells just can't get any bigger, and it is at this point that the system decides that we need more fat cells." "The bad news is once we have this increased number of fat cells, they're there to stay." "We'll never lose them again, and their job description is, to as effectively as possible, accumulate as much fat as they can." "So once we have these fat cells there, it is almost impossible to get rid of them, and we will be much more prone to be overweight at that point." "Research shows that it is much easier for our body to make extra fat cells during our childhood and adolescence, which means that a chubby stage when you're growing up can affect you for the rest of your life." "However hard you try, you can never reduce the number of fat cells in your body." "And the more of them you have, the more likely you are to put on weight easily." "Put simply, overweight children are extremely likely to end up as overweight adults." "As children, our volunteers were always slim, and that's part of the reason why they find it easy" "Second to last day." "Wahoo!" "How are you?" "Not too bad, thanks." "You?" "Good, thank you." "Even now, after four weeks of over-feeding, none of the volunteers have become clinically overweight, but that's not to say that some of them haven't got significantly fatter." "It's time for the final results." "Were the Vermont experimenters right?" "Will there really be much difference coped with the extra calories?" "I have the final results." "So in second place, with 9% weight gain, which is equivalent of 5.5kg, is Thomas Patel-Campbell." "Yeah!" "And in first place, Thomas Hampton, with 9.5% weight gain, which is equivalent of 6.5kg." "Respect!" "In the beginning, I was all talk, and now I'm all trousers." "And the findings absolutely confirm the Vermont study." "Thomas Hampton's 9.5 increase in body weight is nearly double that of Jonathan DeCorday-Long who only put on an extra 5.5%, but the most intriguing result is Martin Wong." "His weight gain of 8%, or 4.5kg, was in the mid-range for the boys, but his appearance hasn't changed at all." "Compared to some of the others doing the study, it's not that noticeable that I have a belly, and I don't know where the fat has gone." "Could be anywhere!" "For the last time!" "According to the Bodpod, the answer is that he hasn't put on much fat." "His body fat percentage has only gone up slightly, by 2.4%." "So if it's not fat, what is it that accounts for his weight gain?" "Martin's an interesting case." "He's gained a lot of weight." "We know it's not a lot of fat, but what he did increase is his basal metabolic rate." "Martin's base metabolic rate has gone up by an incredible 30% during the experiment." "The reason why we think Martin's metabolic rate has increased is because he's actually gained a lot of muscle mass, and muscle needs more energy." "Muscle tissue has a higher metabolic rate than, for example, fat or bone, and if you have an increase in muscle mass, you will also see a dramatic increase in basal metabolic rate." "So even though Martin hasn't been working out or doing any exercise, he's become more muscly." "Studies have shown that this tendency to lay down muscle rather than fat when we over-eat is genetically determined." "But what about the results of the other volunteers?" "Neither Jonathan DeCorday-Long nor Victoria Pagner put on much weight compared to the two Thomases, but their base metabolic rate didn't change significantly either." "One possible explanation is that they've increased their fidgeting." "The body actually tried to get rid of energy by moving their hands, moving their feet, maybe moving their head more than they would have before, because all of that takes energy and the body will protect itself from gaining excessive amount of weight" "by burning this unnecessary energy." "And amongst the group, there are two participants explanation for why some people find it hard to put on weight." "Physically eating enough food was a challenge for many of the volunteers, but Ben and Aisha were the only two who actually failed to reach their calorie targets." "As much as I tried to get the calories in, there is no room." "Every mouthful that I take is a struggle," "I am having to fight a gag reflex to swallow, and each mouthful makes me feel worse and worse and worse, and I know from the experience of the first couple of weeks that if you keep pushing when you get to that stage," "eventually you throw up anyway." "Ben and Aisha interestingly could not consume as many calories as they were set as a target." "Now the reason for this is their bodies were trying to protect it from gaining excessive amounts of weight." "The way the body was doing that is by increasing their fullness by natural mechanisms, natural hormones that come from the stomach and actually blocks you eating more food." "What our study has shown is that there are big variations in the way our bodies behave when faced with excess calories." "It's clear that when it comes to staying slim, there's a lot more to it than diet and exercise." "The lucky ones amongst us seem to have bodies that are built to actively resist weight gain." "But that's not quite the end of the story." "What about the vexed question of losing weight?" "How will our volunteers face getting back to their original shapes?" "Why some of us find it so hard to lose weight is a question that fascinates Dr Leibel's team at Columbia University." "Over the last few years, they have been carrying out an extreme experiment on a group of obese volunteers." "Their human lab rats spend up to two years living under constant observation on the wards at the clinical research centre." "First they starved them, so that they lost 10% of their body weight." "they needed to maintain this weight." "In our most recent studies, we've examined the effects of a 10% reduction in body weight and maintenance of that lower body weight on these individuals." "Despite being fed enough calories, they themselves report persistent hunger." "Dr Leibel found that the patients' brains were still responding to food as if they were starving." "Using modern brain-imaging techniques, in the location and degree of activity of brain centres in response to weight loss in these individuals, and these patterns are consistent with those one might imagine would be present in an individual who was in a state of semi-starvation." "According to Dr Leibel, that's because their body regards their obese weight as the correct weight for them, and it's fighting to bring them back to their original larger size." "So the biology of the regulation of body weight is such that an otherwise successfully weight-reduced obese individual is going to have to live with more or less constant sensation of hunger if they intend to be able to maintain that reduced body weight indefinitely." "But what's bad news for the obese patients is good news for our volunteers." "Their slimmer starting weights are what their bodies consider normal." "So now the experiment has ended, they should have little trouble getting back to their original weight." "Just thought I'd show you what happened to my waistline." "Weighed myself on a decent set of scales the other day, and lost all the weight, which is good." "It's been quite a while now since I finished the study, and I'm happy to say that I think I'm completely back to how I was before." "My clothes all fit, and I feel a billion times better." "I haven't done anything to try and lose the weight." "I think I've lost most of the weight." "I've gone down in all my belts, and they're all back to the right button hole." "After two weeks, considering I put on 5.5kg and something like six or seven centimetres around my waist, that's pretty good." "One month after the experiment finished, the volunteers had lost most or all of their additional body fat." "Their experiences support the feeling that our bodies have their own idea about what weight they want us to be." "Individuals have a biology which determines how tall or short they will be, and individuals have a biology that determines how skinny or fat they will be, and wishing it one way or the other really can't change it very much." "But that's not to say we should give up trying to shift any excess pounds." "What may be depressing for many people who are overweight to know that actually a large amount of weight loss is very difficult to maintain in the long term." "However, we know that small amounts of weight loss will make you healthier, and actually it's much easier to maintain." "As for our volunteers, taking part in the experiment may not have changed the way they look, but it has changed the way they think." "I mean, I know the calorie content of everything now." "I mean, it's quite annoying for some of my friends, and my girlfriend especially, you know, "Shouldn't eat that, that's 800 calories."" ""Shouldn't eat that, oh, 1,200."" ""That pizza, Meat Feast, forget it!"" "I think, certainly this has changed my attitude to my own body." "I mean... ..I found that actually my body can be quite resilient, but only within certain limits." "I'm not sure I'll ever eat another croissant." "Subtitles by Red Bee Media Ltd" "E-mail subtitling@bbc.co.uk"