Why are thin people not fat? (Horizon)

Philipp Scherer demonstrates a tenth of the body fat we would find in a lean person

Philipp Scherer demonstrates a tenth of the body fat we would find in a lean person

Broadcaster: BBC4 (originally BBC2)

Year: 2015 (originally January 2009)

Genre: Documentary

URL: http://bobnational.net/record/284706 *

Review by Lorna McCall

This episode of the documentary series Horizon follows an experiment conducted by Swedish scientist Fredrik Nystrom. In contrast to most studies on obesity, which focus on the laready-overweight, Nystrom takes a novel approach by studying individuals who struggle to put on weight. This programme delves into many different factors the body employs to control our body weight. The following times indicate the start of relevant sections (which are also provided as clips):

  • 03:30 (clip http://bobnational.net/record/286259) This study replicates an earlier experiment conducted in 1967 at Vermont State Prison. Prisoners were offered early release if they could achieve 25% increase in their body weight. Although many inmates did achieve this target, a small handful seemed unable to gain enough weight. One remained resolutely stuck at 18% increase, even when eating 10000 calories a day. This seemed to suggest that for some individuals becoming obese was actually impossible.
  • 05:28 (clip http://bobnational.net/record/286260) In Nystrom’s experiment the male volunteers will eat 5000 calories a day for one month (the women presumably slightly less, though this is not stated). They will not able to do any exercise and will be restricted to 5000 steps/ 2miles walking per day. Importantly (and reflecting a difference from the ethical standards of previous generations) Nystrom will remove any participants from the trial if and when they reach a 15% increase in body mass, above which they may be doing significant damage to themselves (see 07:15 for this statement).
  • 08:25 (clip http://bobnational.net/record/286296) Fat stores are important in the body as they provide energy in a fasted state. They are the highest energy store in the body; metabolism of fats produces more energy per molecule than other sources such as sugars. Dr Philipp Scherer states that an average person, provided with no more additional nutrients than water and minerals, could live solely off their fat stores for one month. In a fed state the fat cells expand until they reach a certain limit. At this limit they divide and produce more cells, this process is irreversible. Once the cells are made they are never destroyed. This means individuals who were once overweight are more prone to returning to an obese state. These stores are easily produced during childhood and adolescence.
  • 11:30 (clip http://bobnational.net/record/286298) In terms of evolution, the ability to lay down large amounts of stored fat has been a selective advantage. Hunter-gatherer populations would experience periods of fed and famine. Individuals who gained much fat in the fed state would survive better in the famine state; as the commentary by Peter Capaldi quips it meant “survival of the fattest”. However as society has changed it is no longer advantageous to be able to store fat readily. Slimmer people are more likely to have healthier and longer lives.
  • 13:50 (clip http://bobnational.net/record/286300) Prior to the start of the experiment, baseline data is recorded on all the recruits. As well as height and weight, the participants are placed in a “bod pod” which records other physiological data.  This section might be useful in discussion of exactly how this kind of research might be conducted.
  • 17:27 (clip http://bobnational.net/record/286302) Studies by Rudy Leibel have revealed that the average body weight remains fairly stable during our lives; it corresponds to eating around 10 extra calories every day. It is highly unlikely, Liebel suggests, that the control of weight is conscious, therefore there must be an underlying biological control employed.
  • 19:25 (clip http://bobnational.net/record/286304) David Allison explains that research has uncovered various influences of our time in the womb upon our later weight. It has been shown that older mothers tend to have children who are ‘fatter’ than younger mothers. The weight and nutrition of mothers at the time of pregnancy can also make their children more likely to be overweight.
  • 28:32 (clip http://bobnational.net/record/286306) Psychologist Jane Wardle has studied the basis of our appetite and how early this is determined. Wardle measures the variant of the FTO gene in children, and how this corresponds to their eating behaviour. Children with a ‘protective’ variant of the gene are able to resist food once they are full, they lose interest in it. However children with another variant will continue to eat food even in a fed state. This genetic basis to appetite may pre-determine the likelihood of individuals to put on weight later in life [This link goes to a UCL press release about Prof Wardle’s research]
  • 37:31 (clip http://bobnational.net/record/286308) As well as variation in appetite, there is a suggestion that some individuals also have the ability to increase their basal metabolic rate in times of higher fed state. This burns the extra calories as heat instead of laying them down as fat.
  • 39:07 (clip http://bobnational.net/record/286309) Another contributory factor in obesity may be due to infection. The Oedema virus SMAM-1 has shown association with obesity. Nikhil Dhurandhar has shown that 20% of overweight patients in his study had previously been infected with the adenovirus. He also discovered that even with patients in the ‘non-obese’ category, those that were generally heavier had also been infected by the virus. SMAM-1 enters the fat cells in the body and replicates. This causes the fat cells to expand and replicate increasing the ability to lay down fat stores. [See this link for a research article on SMAM-1].
  • 44:18 (clip http://bobnational.net/record/286311) Underneath the skin, two different changes might contribute to an increase in fat; we might increase the size of our fat cells and/or increase their number. Philipp Scherer explains that initially our body responds to a higher energy intake by increasing the size of our fat cells. If however they cannot expand any more, we then make additional fat cells. This is a crucial step – the extra cells that are made are kept for life, meaning we will retain a propensity to get overweight more easily.
  • 47:50 (clip http://bobnational.net/record/286312) The results of Nystrom’s study confirmed the results of the Vermont study. Volunteers varied in the amount of weight they put on. Interestingly, one individual showed a 30% increase in his basal metabolic rate, which was attributed to the fact that he had laid down additional muscle rather than fat (which is believed to depend on genetic factors, though these are not discussed). A researcher also explains that some of the participants may have unconsciously resisted weight gain by fidgeting more. Other volunteers also found it physically difficult to eat the required daily calorie intake. Hormones in the body can act protectively to increase the ‘fullness’ sensation and therefore prevent individuals from eating more food.
  • 52:56 (clip http://bobnational.net/record/286314) After the experiment the volunteers found it relatively easy to lose the weight, without having to diet. Leibel has shown that this is due to the body retaining a memory of the ‘correct’ body weight. In obese individuals this means that on losing a large amount of weight the body will constantly try to return back to the ‘correct’ larger weight. However in the slim volunteers the body is able to easily return it back to its original starting weight.

Overall, this programme highlights many different mechanism the body uses to pre-determine and control body weight and susceptibility towards obesity. Discovery of these genetic and other factors may provide better understanding as to how people become overweight and what treatments can be administered to help lose weight or prevent obesity in the first place.

*The link goes to a later broadcast of this programme because, unlike the original recording, this copy includes both a transcript and frame recognition. The BBC page for this episode (not the programme itself) is available here. and the IMDb page is here.


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