Horizon – Why Are Thin People Not Fat?

It is estimated that there are now more people on the planet at risk from obesity-related diseases than there are suffering from starvation. Western society in the 21st century is eating itself into an early grave but, while the ranks of the overweight and obese are swelling, there is a significant proportion of the population who are apparently immune to this phenomenon.

Horizon – the BBC’s flagship science strand – sets out to discover what is keeping these people thin. Are some people really able to consume as much as they like without becoming obese? If so, how do they do it?

Ten volunteers have agreed to eat double their normal intake of calories over four weeks to see how their bodies cope with a month-long chocolate, cake and fast-food frenzy.

The test is based on a 1967 experiment on Vermont State Prison inmates, in which medical researcher Ethan Simms recruited a group of prisoners to eat as much as they could until they had gained an extra 25 per cent of their original body weight. The reward was early release. Despite eating up to 10,000 calories per day, only six of the nine who took part succeeded. The experiment seemed to show that, however available and calorie-rich food is, not everyone will become overweight.

More than 40 years on, Horizon, with the help of Swedish scientist Fredrik Nystrom from the University of Linkoping, follows the volunteers over the course of the month to find out what is happening to the extra calories they are consuming, and why their bodies respond in such different ways.

Horizon also meets Professor Jane Wardle from University College London, who is exploring whether eating habits are genetic or learned, and Dr Nikhil Dhurandhar, who believes a virus could be responsible for some cases of obesity.

The programme asks whether obesity has an evolutionary advantage, if there could be a genetic basis to will-power, and whether people have a natural weight that their bodies strive to maintain, however much they eat or exercise.

Monday 26 January
9.00-10.00pm BBC TWO

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