Lesen Sie diesen Artikel auch auf Deutsch.

Nearly 40 years ago, Western governments, after consulting with the world’s top nutrition scientists, told us to change the way we eat. If we wanted to stay healthy, they said, we needed to cut back on foods rich in saturated fats and cholesterol. 

By and large, we did as we were told. At least in Western industrialized countries. Steak and sausages were replaced with pasta and rice, butter with margarine and vegetable oils, and eggs with muesli. But instead of becoming healthier, we grew fatter and sicker. In the decades that followed the issuing of these dietary guidelines, a public health catastrophe unfolded in many countries, foremost America and the UK. Obesity, which until then had been relatively stable, rose dramatically, as did the incidence of related diseases, like diabetes.

What went wrong?

This was a foreseeable disaster, which could have been avoided – were it not for the arrogance and myopia of the experts in whom we placed our trust. Back in 1972 a British scientist warned the world that the real threat to our health was not fat, but sugar. But no one listened to him: John Yudkin. In a book called "Pure, White and Deadly", he wrote: "If only a small fraction of what we know about the effects of sugar were to be revealed in relation to any other material used as a food additive, that material would promptly be banned".

The book did well enough, but Yudkin paid a high price for it. Prominent nutrition scientists combined with the food industry to destroy his reputation. His career never recovered. He died, in 1995, a disappointed, largely forgotten man. 

By the time Yudkin wrote his book, most nutrition scientists had signed up to a different theory; one that had emerged, a decade or so before, from the United States. Its central tenet was that a healthy diet is a low-fat diet. Yudkin, a professor of nutrition at Queen Elizabeth College in London, led a diminishing band of dissenters who believed that sugar, not fat, was the more likely cause of maladies such as obesity, heart disease and diabetes. 

Yudkin noted that sugar has been a major part of Western diets for just 300 years; in evolutionary terms, it is as if we have, just this second, taken our first dose of it. Saturated fats, by contrast, are so intimately bound up with our evolution that they are abundantly present in breast milk. To Yudkin’s thinking, it seemed more likely to be the recent innovation, rather than the prehistoric staple, making us sick. He also believed that the evidence that fat is bad for us was relatively weak. 

But the commanding heights of his field had been seized by proponents of the fat hypothesis. The American scientists who made up the world’s nutritional elite were skilled at political combat, and didn’t hesitate to take down the reputation of anyone who challenged their ideas. On their advice, American and European governments told their citizens to cut back on fat and cholesterol-rich foods. 

Sugar is the most unhealthy carbohydrate of all

Yudkin, whose ideas about sugar had previously been considered perfectly mainstream, quickly found himself marginalised. He was disinvited to scientific conferences, and shunned by scientific journals. His research eventually fell out of circulation altogether, and the story of his swift demise scared off any other scientists interested in challenging the consensus that fat was the chief problem with our diets. 

When people cut back on fat, they usually increase their consumption of carbohydrates. It is now becoming increasingly apparent that by turning saturated fats into our number one dietary enemy, we missed the greater threat of the most versatile, palatable and unhealthy carbohydrate of all: sugar. 

Only in the last 10 years has it become acceptable again, in scientific circles, to even research what sugar does to our bodies. At the same time, several comprehensive scientific reviews have found little or no evidence that saturated fats cause heart disease or cancer. The paediatrician and obesity expert Robert Lustig has led the way, after studying sugar’s effects on the metabolic system. A 90-minute talk he gave in 2009, titled "Sugar: The Bitter Truth", has been viewed more than 6 million times on YouTube

Lustig now champions Yudkin’s research, but it was so well buried that he only came across it by accident, when a fellow scientist mentioned it to him at a conference. Lustig was astonished to find that it anticipated his own work. When I asked him why he was the first scientist in years to focus on the dangers of sugar, he told me: "John Yudkin. They took him down so severely – so severely – that nobody wanted to attempt it on their own."

A growing body of evidence suggests that obesity and diabetes are driven not simply by the number of calories we consume, but how we get them – and that sugar calories are particularly bad for us. A recent study, led by Sanjay Basu of Stanford University (PlosOne: Basu et al., 2013), evaluated the level of sugar in the food supply of 175 countries. It found that the prevalence of type 2 diabetes in a population increases 11 times faster when people consumed more calories from sugar sources, than from non-sugar sources, independent of average exercise levels or body-mass index.

After all, it’s not exactly news that sugar is bad for us. The British government recently recognised the urgency of the problem, by introducing a tax on sugary drinks, following the example of other countries, including France. On reflection, however, I think the article tapped into something powerful and not yet fully acknowledged: a sense that the scientists and government officials, on whom we all rely for good advice, got it dreadfully wrong. 

The obesity epidemic is sometimes talked about as if it was an act of nature, or an unfortunate accident. If anyone is blamed for it, it’s usually the food industry and certainly, the food companies have a lot to answer for. But if the nutritional advice most of us have followed for all this time was profoundly flawed, this is not a mistake that can be laid at the door of corporate villains. Nor can it be passed off as simple error; what happened to John Yudkin suggests otherwise. No – this is something the scientists and officials did to themselves, and, consequently, to us.

For the full story of "The Sugar Conspiracy", published as a long read in The Guardian, click here. An audio version is also available in English.