Diets don't work and here's why

Diets don’t work, says Dr Giles Yeo who believes we should focus on health not weight. Marjorie Brennan reports.

Diets are nothing new but what we eat has become an increasingly emotive topic in recent years. Whether it is ‘clean’ eating, paleo or veganism, the explosion of social media has amplified the physical, psychological and ethical issues surrounding what we consume and why, often making food something to be feared rather than enjoyed.

Someone who is well aware of this is scientist and broadcaster Dr Giles Yeo. When he presented a programme for the BBC two years ago about the ‘clean’ eating fad, the backlash from those involved in promoting the movement was fierce.

“The response I got from that, and the fact I raised the ire of so many evangelical dietary people, got me interested in how we think and talk about diets,” he says.

The result is the book Gene Eating, in which Yeo, a geneticist at Cambridge University, explores the science of obesity and why diets don’t work. He is keen to debunk the myths which underlie much of the dietary advice people now access online.

“Social media has democratised journalism — anyone can go online and create a blog and there is no editorial control. We have an immense obesity problem and people are looking online to find solutions because scientists are taking so long to find answers. That’s why I wrote the book because I wanted to contribute something positive by at least giving people access to what I’d like to think is non-BS information.”

Yeo says he feels a responsibility to address the maelstrom of misinformation and marketing speak circulating on social media platforms.

“As an academic and scientist, I think as a community, we must take some of the blame. I’ve got quite a few colleagues who consider my non-academic work — the broadcasting and so on — a waste of time. My answer is that if we the ‘experts’ won’t tell people what we’re doing, or explain our respective scientific methods, that if we argue with each other, and change our minds regarding the evidence, then others who are not experts are going to fill that space.”

Yeo’s programme fired a shot across the bows of the clean eating movement, echoing many people’s concerns, in particular, that it was just an excuse for disordered eating or orthorexia — a fixation with ‘proper’ eating that can be damaging to health.

“Clean eating is not even one type of eating, it’s a whole suite of different types of behaviour that people practise,” says Yeo. “They tend to be involved in removing entire groups of food for no scientific reason — that’s the first thing. Second, they do tend to believe food is medicine. That’s not to say that food doesn’t play a role in our health, of course, it does, but it doesn’t mean if you have cancer, stop chemo and eat certain foods, that that will cure you.”

While it is fair to say that the clean eating bandwagon has been and gone, would Yeo be concerned that the increasing popularity of veganism, often pursued in terms of ‘wellness’, holds similar dangers?

Veganism, wellness and any number of detoxes out there — I believe that people are making decisions about these diets for the wrong reasons. Also, extreme diets like paleo, just because they’re eating meat rather than vegetables, they’re equally evangelical

Yeo went vegan for a month for one of his TV programmes but cautions that it is not an option for everyone.

“As a strategy it helped me reduce my calories. I draw a distinction, a big one, between veganism and vegetarianism. A lot of people in the past would almost have been vegetarian anyway because they couldn’t afford meat, while they could afford eggs and milk, which were nutritionally dense. I think vegetarianism is something we could all do, and it is cheap.”

He says that the vegan diet as practised in a wealthy, consumer-focused society is often based on access to ingredients and money, and adherents can be just as evangelical.

“A lot of diets, and veganism is one in particular, are a first-world privilege.

“Yes, you could do it cheaply but you’d really have to think about it. You also have to supplement, for example, think about where’ll you get B12 vitamins from. You have to eat a lot of vegan food to match a steak, so you end up losing weight, which is fine, but before you force your dietary choice on someone else, remember there are people who don’t have a choice and who don’t have the privilege to make that choice.”

As a researcher, Yeo was in the vanguard of describing a number of genes that, when mutated, resulted in rare forms of severe obesity, uncovering key pathways in the brain that control food intake. He argues that it is important that obese people are not seen as bad or morally weak as often they are fighting their biology and genes.

“If your genes make you feel hungrier or make it difficult for you to say no to certain foods, it’s hard to lose weight. I use the terms obese, fat and overweight in a non-pejorative way — we should be able to describe the problem without judging the person suffering from the problem. People say ‘oh, you’re giving people an excuse’. I’m not. Or ‘you’re blaming fat people’. I’m not. ‘You’re saying being fat is good’. I’m not.

You may eat too much because of your genes, but you still need to eat less to lose weight, otherwise, you’re going to die

Yeo also says that when it comes to losing weight, counting calories isn’t necessarily a good way of measuring what we are actually consuming in terms of energy. This is because different foods have different ‘caloric availability’ — the number of calories digestion can extract from a food versus the number of actual calories in the food.

“An example I give in the book is 100 calories of sugar — the likelihood is you’ll get close to 100 calories out of that. But then take 100 calories of sweetcorn — eat that and look in the loo the next day, you clearly have not absorbed anywhere close to 100 calories of sweetcorn.

“We should also consider the different macronutrients. For example, refined carbohydrates are over 95% available — so for every 100 calories, you eat you get over 95 calories. The same is true for fat, which is also nutritionally dense. Protein, on average, is 70% available. So for every 100 calories of protein, you eat on average you extract 70 calories, depending on the type of protein it is and how it’s cooked, etc. So there’s a difference between eating 100 calories of steak and 100 calories of sugar.”

In terms of his own eating habits, Yeo is among the growing number of people cutting back on meat, but it is not something he could give up entirely.

“I lost weight on a vegan diet but I started gaining weight very quickly when I switched back to meat.

“But I like meat and eggs too much to give them up entirely so I switched to flexitarian, where I’m vegan pretty much every lunch during the week and two evenings.

“My meat intake has probably dropped 40% and my weight has gone back to my ‘vegan weight’. It’s about moderation — I like my steak but understand I need to eat less meat.”

Yeo also believes that BMI [body mass index] isn’t necessarily the best indicator of general wellbeing and it is more important to be healthy than the right weight.

“Each of us can carry different types of fat safely. This is why you have skinny people with type 2 diabetes and fat people who don’t. I think if you worry about your health your weight will take care of itself.

“Does it mean you’ll look like Angelina Jolie? Not necessarily, unless you have good genes, but it’s more important to worry about health than weight, even if you don’t have what you think is the ideal body.

“If you’re physically active and able to do the things you want to do — even if your BMI is over 25 — then that’s more important.”

Yeo hopes that people will take away many insights from his book but if there is one lesson that is key, it’s that the one-size-fits- all approach doesn’t work when it comes to staying at a healthy weight.

“For diets to work you have to stay on that specific diet, which means anything extreme is untenable.

“You have to find something that suits your lifestyle, that’s moderate, otherwise, you won’t stick to it.”

Gene Eating: The science of obesity and the truth about diets by Dr Giles Yeo is published by Seven Dials


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