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The flimsy evidence behind low-fat diets

My Times column on low-fat diets and the evdience behind them:

The diet police are on the prowl: if you hear a knock on the door, hide the sugar bowl, the butter dish and the salt. A draft report from the scientific advisory committee on nutrition said last week that we should halve our intake of sugar. The campaign group Action on Sugar wants “a total ban on advertising of ultra-processed foods that are high in saturated fats, sugar and salt, and sweetened soft drinks, to protect children”.

I have been curious about this new demonisation of sugar. I now realise that it conceals a grudging admission that fat is not bad for you after all, but the experts cannot bring themselves to say so. There is a strong possibility that the “diabesity” epidemic has been caused largely by the diet police themselves.

So argues a devastating new book: The Big Fat Surprise by Nina Teicholz, an experienced journalist who spent eight years tracking down all the evidence for and against the advice to eat low-fat diets. She finds that it was based on flimsy evidence, supported by an intolerant consensus backed by vested interests and amplified by a docile press. And it made us fatter.

In the 1950s heart disease had come from nowhere to be a big killer in America, especially of men in middle age. Although we now know that cigarettes were a huge cause — and the sharp recent decline of deaths from heart disease is mainly due to people smoking less, plus better treatments — scientists quickly decided that eating fat was the cause. Cholesterol clogs arteries, so eating high-saturated-fat food such as meat, eggs and dairy products must cause high cholesterol in the blood. Plus, eating fat makes you fat. Obviously, no?

The chief source of the anti-saturated-fat message was a politically astute scientist named Ancel Keys. In 1961 he persuaded the American Heart Association to issue guidelines on saturated fat intake. The main evidence came from his study of heart disease in six countries in Europe plus Japan, from which he concluded that low-fat diets led to less heart disease.

Yet the data in the study were awful, Teicholz says. Keys left out countries that he knew produced inconvenient results, most of his low-fat countries were ones still recovering from wartime starvation, his dietary evidence came from a tiny subset of the men in his clinical sample, and his lowest-fat diet was from Crete during Lent, when meat-eating all but ceased. He published results in obscure German journals. Teicholz told me these were huge methodological problems, which should have called the entire study into question.

Even so, the fat effect was weak: an order of magnitude less than the effect of cigarettes on cancer, for example. Yet it was on this feeble and dodgy dossier that an entire edifice of advice was built. Sceptics kept pointing out inconvenient facts, but were ignored. How come native Americans, Inuit and Masai ate mostly meat and fat but had almost no heart disease or obesity, while they immediately got both when they started eating bread and potatoes? How come controlled trials of veterans and prisoners found that substituting vegetable oils for animal fats caused no change of overall mortality rates?

Anyway, we now know it just is not true that eating fat is what makes you fat. The body does not shunt butter directly to your thighs; it processes all food and adds to or draws down from fat reserves based on hormonal signals. Fat has more calories per unit of weight, but it’s also more satiating. All the best evidence now suggests that it’s easier to gain weight on a high-carb than a high-fat diet because the latter is more filling.

The sceptics were silenced by Keys and his allies and howled down by obedient journalists, a profession in love with conventional wisdom. Teicholz documents how the fat folk reviewed each other’s papers, funded each other’s projects and kept the doubters out, so that they gradually left the field. (Reminiscent of modern debates on climate change?)

The American Heart Association, built up into a major force with funding from the vegetable-oil industry, relentlessly pushed the message that animal fat was bad. The US government issued guidelines in 1978. We in Europe followed suit, as we tend to do. And the message was driven home in the culture. Low-fat became a craze. It still is: look at supermarket shelves.

In the past ten years, study after rigorous study has found that animal fat per se is not harmful, does not cause obesity, does not raise the kinds of cholesterol that predict heart attacks, does not increase death rate and is healthier than carbohydrates. For instance, one two-year trial in Israel found that a fat-and-meat “Atkins” diet lowered weight more than either a low-fat or a Mediterranean diet. As Teicholz puts it in her book: “Every plank in the case against saturated fat has, upon rigorous examination, crumbled away.”

Such findings remain too heretical for most diet experts. Those who make them struggle for years to get published and have to couch their findings in cautious language. Those such as Teicholz and Gary Taubes who write books pointing out that this fat emperor had no clothes are treated as pariahs. If anything, the official committees of the diet police are doubling down, demanding that we eat ever less saturated fat.

However, they are also now shifting the emphasis of their disapproval to sugar. In fact, while the evidence against carbohydrates in general as the cause of obesity and diabetes is good, the evidence against refined sugar being peculiarly evil is not. And there’s a real problem developing. If we are to condemn carbs and sugar (and therefore fruit), and still condemn fat and red meat (as Action on Sugar does), then there’s not much left to eat except sea bass and spinach. Which is not practical.

The message is all stick and no carrot, which is no way to win people round. So here’s a suggestion for the diet police: put out a poster saying “We now think you should eat less sugar and bread, but that you should feel free to eat more eggs, meat and cheese again (but we might be wrong)”.

The subtitle of Teicholz’s book is: “Why butter, meat and cheese belong in a healthy diet.” Yesterday I cooked bacon and eggs for my breakfast. And by the way, I don’t have a vested interest: my farm has a dairy herd, but then it also grows wheat and vegetable oil.

By Matt Ridley | Tagged:  rational-optimist  the-times