Tuesday 22 October 2019

Eating for your genes: the 'anti-diet' revolution

Renowned geneticist and author of the anti-diet book Gene Eating: The Science of Obesity and the Truth About Diets, Dr Giles Yeo, talks to Katie Byrne about how our genes influence how hungry we feel and how much we eat - and explains what we can do about it

Dr Yeo says obesity is an incredibly complex problem
Dr Yeo says obesity is an incredibly complex problem

As a man who relies on evidence-based science, Giles Yeo has always been wary of the unsubstantiated claims that are peddled by the diet industry.

The Cambridge geneticist has been studying the brain control of food intake for nearly 20 years and he has come to the conclusion that obesity is an incredibly complex problem - further complicated by the 'revolutionary' claims made by diet book authors.

Yeo's debut book, Gene Eating: The Science of Obesity and the Truth About Diets, arrived in shops earlier this year - but he wasn't trying to make a quick buck out of the 'New Year, New You' January diet craze.

On the contrary, his "anti-diet" book is, as he puts it, "a structured diatribe against dietary misinformation backed by bad (or no) science".

"What I'm hoping by putting this book out is to give people at least a chance at taking a new fad diet and unpicking it," explains Yeo.

"I want people to look at [diets] and think: is this total BS, or is there something real there that I might want to try?"

One-size-fits-all diets

Readers will probably know Yeo from his work with BBC science programme Horizon. He highlighted the drawbacks of one-size-fits-all diet plans in 'What's The Right Diet For You?' and earned the eternal wrath of the plant-based diet community after 'Clean Eating: The Dirty Truth' first aired in 2017.

Gene Eating follows in the same vein. Painstakingly researched yet surprisingly entertaining, the book takes aim at many modern dieting trends - in particular the use of the words 'clean' and 'real' to describe certain foods.

"If some foods are labelled clean or real," he explains, "then the rest must, by definition, be 'dirty' or 'false' to some degree. Hence, through guilt by association with our diet, some of us could be considered 'clean' and others 'dirty'. I could be 'real' and you could be 'false'."

The pseudoscience of juice cleanses and detox diets is also pulled apart. Advocates of these diets often talk about giving the liver a much-needed break but Yeo points out that there is no evidence to suggest that food "can accelerate or enhance this process".

"The situation in which actual bona fide 'detoxification' is needed is when someone is being treated for a dangerous level of a substance that is life-threatening," he explains matter-of-factly.

Even good old-fashioned calorie-counting is called into question. All foods have different "caloric availability", explains Yeo, meaning that not all calories are processed by our bodies equally. The caloric availability of protein, for example, is 70pc, meaning we absorb, on average, 70Kcal for every 100Kcal consumed.

"Sadly, no matter how much one doth protest, the only way you can gain weight, is if you eat more than you burn," he says.

"The reason we have become more obese as a species is because we eat too much and don't move enough. Therefore, the only way to become less obese is to eat less and move more."

Environmental actors

Yeo says environmental factors have driven the rapid increase in the prevalence of obesity, but it is now becoming clear that our genes have influenced our response to this change.

To put it more simply, some people have a genetic predisposition to obesity before they even consider the many and varied ways that their lifestyle might be widening their waistline.

Take Yeo as an example. He can average over 30 miles a day on his bike, while a heart monitor device that he wears estimates that he expends around 900-1,000 calories a day through this activity.

And still he has a "wobbly tummy", a BMI of 26 and a vision of what he might look like if he didn't exercise.

"My wife always wonders, with equal frustration and amazement, why I am not as skinny as a rake," he says.

"Obese people are not lazy, or weak, or morally bereft," he continues. "They are fighting their genes, they are struggling against their biology. Until we in society understand that, until we are able to remove the stigma from being obese, we are never, ever, going to be able to fix the problem.

"Yes, you may argue that some people might use that as an excuse - and that's a fair point - there are people who will use it as a genetic crutch and I can't do anything about that."

The idea that we are held hostage by the genes that we inherit from our parents is disheartening, especially for those who have tried - and failed - to shift weight.

Gene-editing techniques

However, if genes are the problem, perhaps they are also the solution. In other words, maybe we'll one day be able to reverse obesity with gene-editing technology?

Yeo is careful to reframe the query before he gives it consideration.

"Can we use gene-editing techniques for certain rare obesity conditions, in which you have an actual mutation in an actual gene causing an actual disease: severe obesity?" he asks.

"Ethics aside, that should be fixable - because we're talking about one gene. The problem - and the reason why I'm a couple of kilos overweight - is that it's not going to be down to one gene. It's going to be down to multiple genes.

"At the moment - certainly in the next decade or so - I can't see there being techniques available to make hundreds of changes in an embryo.

"Now, are we going to get to the point where we can take a genetic test from a baby and predict if he or she is going to become obese... I think that is something that is plausible."

In the meantime, Yeo thinks the diet industry will continue to boom as people seek out easy answers to complex problems.

"I don't blame people for wanting easy answers because losing weight is difficult," he says.

"It's unpleasant and, given that, if something seems less hard, there will always be customers for it."

If you are one of these customers, it's worth pointing out that Gene Eating won't give you the magic bullet for weight loss.

It will, however, help you understand the science of obesity and the pseudoscience behind the most popular fad diets.

The secret is that there is no secret. And amidst the 'life-changing' claims made by the diet industry, some scientific rationale might just prove to be a game-changer.


Gene Eating: The Science of Obesity and the Truth about Diets by Dr Giles Yeo is published by Seven Dials (€20.99)

Health & Living

Editors Choice

Also in Life