Amanda is Healthy Food Guide's nutrition editor with a degree in nutrition and a post-grad diploma in dietetics. She is a member of the British Dietetic Association, The Nutrition Society and The Guild of Food...

How do some people stay slim without dieting or exercising?

We all know one – that lucky individual who eats whatever and as much as they fancy, does nothing more active than lift the remote control – and never puts so much as an extra inch on their waistline. We tend to say things like ‘she eats like a horse,’ or ‘he has a metabolism like a Ferrari,’ or ‘they’d get a bus to the next-door neighbour if they could.’ It just doesn’t seem fair!

With that in mind, I came up with a TV programme idea The Truth about slim people that turns the ‘why are we overweight?’ question on its head. It looks at how two slim people – mum of two Ann-Marie and dad of two Yemmi – have remained a steady, normal body mass index during adulthood and into their 30s.

We put the preconceived ideas of why Ann-Marie and Yemmi never gain weight to the test.

We checked their…

> basal metabolic rate (BMR). Physiology experts measured this to see how many calories they burned a day

> activity levels through daily video recordings

> sleep patterns. Researchers logged the total number of hours they slept

> gut microbiome. Scientists looked for certain good bacteria that may be helpful in protecting against weight gain

> eating habits. I looked at their food diaries to tot up the number of calories they were eating daily.


What did we find?
The results were fascinating, yet our cameraman was disappointed because there were no outlandish or extreme findings. Our male and female guinea pigs didn’t burn calories at the speed of lightning. Mundanely, their BMRs were normal.

They were active, but not in the pound-away-in-the-gym and sweat-yourself-to-pieces in a spinning class kind of way. Instead, they burned calories walking fast on the way to work, taking the stairs instead of the escalators twice daily and using energy by fidgeting.
Interestingly, they both had favourable strains of gut bacteria in their stool samples, and both slept soundly as well.

What did they eat?
They didn’t actually eat gargantuan portions of junk, as their nearest and dearest maintained. In fact, their calorie intake matched their calorie output.

On some days and at some meals – all eaten sitting down, by the way – they did appear to wolf food down as though they’d never eat again. Yet balanced over the week, this simply wasn’t the case. A blow-out dinner was compensated the next day by having a small breakfast and tiny lunch. They drank occasional amounts or no alcohol.

The verdict
Ann-Marie and Yemmi both lead healthy lifestyles and eat what their bodies need. There were no world-class revelations for our cameraman.

The million-dollar question, of course, is why do they balance their intake and output of energy so perfectly? Are they genetically programmed not to find food as tasty and appetising as people who struggle with their weight? Do they respond well to sensations of fullness so that they don’t feel the need to over-ride ‘I’m full’ message and keep on eating? Do their happy marriages and family lives offer them a relatively stress free existence that keeps hunger-promoting hormones under control?

These bigger questions have yet to be answered. What we have discovered is that, perhaps not surprisingly, there is no magic bullet.