The dirty truth about 'clean eating' diets that claim to be cure-alls

Why do we fall for pseudo-scientific diets that make false medical claims? Because we want to believe that food can make us well, writes Dr Giles Yeo

Obesity and other diet-related illnesses are easily the greatest public health problem of our time. But losing weight and keeping it off is incredibly difficult; it is not what we are evolved to do.

Over the past 20 years, my research at the University of Cambridge's MRC Metabolic Diseases Unit has focused on the genetics of why some people get fat and some don't.

Science is set up to get to the truth ... eventually. It does not provide quick answers. As a result, there are many desperate people looking for a way out, a silver bullet. Over recent years, a proliferation of, by and large, skinny and attractive food gurus have emerged, armed with dietary advice that is not based on any serious scientific evidence.

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Much of this new advice goes far beyond healthy eating, and in some instances argues that food can actually make you well. Welcome to the world of "clean eating", which I have spent the last few months investigating for a documentary, to understand how scientific these claims really are.

It became clear that many hundreds of thousands of people are more likely to believe the advice of these food gurus - buying their books and following their social media feeds - than listen to scientists taking an evidence-based approach to nutrition.

For healthy-eating devotees, Instagramming everything that passes their lips, the term #clean still reigns supreme. Clean eating is not one way of eating, but encompasses many different dietary approaches. In the documentary, we focused on three of the big beasts: giving up gluten, an alkaline diet, and a plant-based diet.

block_quotes_start Clean eating is not one way of eating, but encompasses many different dietary approaches block_quotes_end

What rapidly emerged was that "post-truth" science permeates the entire culture. This troubling narrative was best illustrated by my surreal visit with so-called doctor Robert Young, father of the "alkaline diet".

If you ignore the pseudo-babble, then what an "alkaline diet" encourages is lots of vegetables with little to no meat. Where's the harm, you might think? Well, when I drove into the hills outside San Diego to see Young on his "pH miracle ranch", I found out.

A manicured millionaire's paradise, preposterously set behind a moat, the ranch was built on the proceeds of his pH Miracle book series, which has sold more than four million copies.

As Young welcomed me, he began to share his alkaline view of the world: "The human body in its perfect state of health is alkaline in its design."

The pH of our blood is 7.4, which is slightly alkaline, so Young is broadly correct, although different body parts, such as our stomach, function at very different pHs. Everything else about "alkaline living", however, is complete fantasy.

Young believes that in order to maintain the alkaline pH of our blood, we have to eat alkaline foods. The problem is, there is no evidence that your blood's pH is influenced by what you eat.

Your stomach, at around pH1.5 (akin to battery acid), is the most acidic environment in your body. So whatever you eat will arrive in your intestine at the same acidic pH.

In fact, nothing, apart from almost dying, will change your blood's pH. So if it does change, you're probably about to die.

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Young's food categories also don't make any sense. Meat is considered "acidic", yet all mammals have alkaline blood.

Equally, certain citrus fruits are considered "alkaline", when they are by any measure acidic. Don't waste time trying to wrap your head around this nonsense. It doesn't stand up to even casual scrutiny.

Yet Young goes further still, claiming that disease emerges from acidity - which he believes transforms blood cells into bacteria by a process he calls pleomorphism - and that, by extension, disease can be reversed with alkalinity.

Can I be crystal clear? Young's view goes against all current scientific understanding. When I posed this to him, he said this is "a new thought, a new consideration". In other words, this is his "post-truth" fantasy.

Last year, Young was convicted of two charges of practising medicine without a licence, and faces up to three years in prison. I asked him if he felt remorse. He said: "I don't have remorse because of the thousands, if not millions, of people that have been helped through the [alkaline-diet] programme."

When pseudo-science goes beyond advising people to eat more vegetables, and is used to manipulate the vulnerable and most ill in society, it becomes a true problem.

The gurus of clean are doing nothing wrong by encouraging healthy eating, but they have a responsibility to ground their promises in proof.

Official health bodies recommend a balanced diet including fruit, vegetables, whole grains and dairy, while limiting meat. And the simple - if unfashionable - truth is that science has, so far, discovered nothing to prove otherwise. — The Daily Telegraph, London

• The author of this article, Dr Giles Yeo, is principal research associate and group leader at Cambridge University's metabolic research labs.