• “An awful lot of people who are overweight have a perfectly normal or even quite a high metabolic rate,” says Prof Brewer says on The Truth About Slim People. (iStockphoto/Getty Images)Source: iStockphoto/Getty Images
A new documentary on SBS - The Truth About Slim People - investigates whether slim people who eat whatever they want but never gain weight just have a fast metabolism or if there are other factors at play.
Yasmin Noone

12 Jun 2018 - 2:21 PM  UPDATED 13 Jun 2018 - 7:45 AM

We’re all told that in order to prevent weight gain or obesity, we need to be mindful of what we eat and exercise regularly.

But what about slim people who eat whatever they like and consume lots of food but never seem to put on weight? Are they slim, as the old adage goes, because they have a faster metabolism than everyone else?

A new documentary on SBS, The Truth About Slim People, airing on Wednesday 13 June at 7.30pm investigates why some people maintain a healthy weight, even if they eat more and move less than everyone else.

“You don’t need to be that much out of sync with your energy expenditure to gradually increase your body weight." 

Professor John Brewer from St Mary’s University, London – who was interviewed in the documentary – says a fast metabolism is not always the reason behind an individual's healthy weight. 

Prof Brewer reasons that many slim people maintain a healthy weight because of their total calorie intake, not their metabolisms. The same may be true in the reverse. “An awful lot of people who are overweight have a perfectly normal or even quite a high metabolic rate,” says Prof Brewer says on The Truth About Slim People. “But they would have undone all of that by taking in too many calories.”

Prof Brewer explains that if your resting metabolic rate is one calorie a minute, your energy needs might be around 2,000 calories a day. If you eat 2,300 calories a day, just because you ate a few extra biscuits, you will gain weight.

“You don’t need to be that much out of sync with your energy expenditure to gradually increase your body weight. You could just eat 100 calories a day more [than what you should]” and after 80 days you would have put on one kilogram of body fat.”

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The documentary features two slim people in the UK: 37-year-old Yemi who is 178 cm tall and weighs 80 kilograms, and the size-eight 41-year-old Anne Marie, who is 170 cm tall and weighs 60 kilograms. Both adults have always maintained a slim figure since childhood without having to diet. Yemi and Anne Marie also have normal metabolisms. 

Over a course of five days, covert cameras followed the two participants everywhere – at work, home and play – to uncover their secrets to being slim. 

The show reveals that although Yemi and Anne Marie eat a lot, they self-regulate their consumption. If they consume large portions or an unhealthy meal one day, they unintentionally eat less food the next day.

"You could just eat 100 calories a day more [than what you should]” and after 80 days you would have put on one kilogram of body fat.”

The participants also shared a few other common characteristics that health experts thought were responsible for their slim physiques.

1. They slept 6-8 hours a night.

Anne Marie averages up to nine hours sleep a night while Yemi has around seven hours a night.

Professor of Cardiovascular Medicine and Epidemiology at University of Warwick, Francesco Cappuccio, says people who sleep less than six hours a night on a regular basis may become overweight or obese.

He believes the relationship between two hormones – leptin, which is produced by fat cells and ghrelin, which is produced by the gut – is what causes the weight gain.

“They are the two hormones that move in a seesaw mechanism,” he says. “When you are full, one goes up and the other one goes down. And when you are hungry they change. When you are sleep deprived, these hormones are deranged so they turn towards an increase in hunger and appetite even if you are not [hungry].”

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2. They drank little or no alcohol.

This meant they were not adding to their calorie intake by consuming the sugars contained in alcohol.

3. They rarely ate out.

Although both Yemi and Anne Marie admit that they eat large portions of food, their meals are mostly cooked at home and cooked from scratch. Processed foods are kept to a minimum, as was dining out or buying take-away dishes.

4. They ate meals sitting down.

Professor of Psychology at the UK’s University of Surrey, Jane Ogden, explains that a recent study revealed that people who ate a meal standing up, ate twice as much after they finished consuming the food. Interviewed for the documentary, Prof Ogden says this may be because the test participants psychologically correlated eating standing up with snacking and therefore considered the food to be a snack, not a meal.

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5. They don’t really snack a lot.

Yemi and Anne Marie ate snacks sometimes but they were usually consumed near their main meals and not late at night.

6. They built an eating and exercise routine into their lives.

Meals were also eaten at regular times during the day.

Both participants also did exercise but beyond the scheduled classes they were each involved in, movement was habitual and part of their daily routine.

“You could possibly drive to work and not remember getting there because your conscious mind is switched off: it’s a learned behaviour,” says Dr Julie Coffey, author and UK GP about the show’s participants and their daily routines.

“These guys [who have been filmed] have learned behaviours that are running on auto-pilot. Their behaviour is serving them well in terms of the weight they are achieving so they don’t have to worry about their weight.”

'The Truth About Slim People' airs on SBS on Wednesday 13 June at 7.30pm. The documentary will be available to stream on SBS On Demand after broadcast. 

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