The full-fat diet – why it’s not as unhealthy as you think

The following article by Michael Mosley was published in The Times on 2nd July 2014 :

Full-Fat DietI saw a study the other day that found that eating yoghurt would help you lose weight. Not surprising, because yoghurt is high in calcium and protein, which keeps you fuller for longer. What was surprising about this study, however, which involved following 8,516 men and women for more than two years, was that the yoghurt had to be full fat to work. Eating low-fat yoghurt didn’t make any difference.

Ever since I was a medical student, several decades ago, I have been convinced that fat is the enemy. Saturated fat, I’ve assured friends and family, will clog your arteries as surely as pouring lard down them. Because it is so energy-dense, eating fat will also, inevitably, mean you pile on the pounds.

Recently, however, I’ve changed my mind. Study after study has failed to find a convincing link between saturated fat and heart disease. As a nation we’re eating less fat but getting fatter. Research has shown that low-fat diets rarely work, that cholesterol is a poor predictor of heart disease and that eating the right kind of fat can be both good for the heart and for slimming. Instead attention has turned to sugar, with obesity experts last week urging people to cut back on fruit juice and sugary drinks.

So what’s going on? Well to understand the fear of fat we need to go back to 1957, the year I was born. It was then that the hugely influential American Heart Association decided to back a campaign aimed at reducing fat consumption. Out with the steak, butter and cheese; in with the pasta, rice and potatoes. Or at least that was the plan.

In that same year a British scientist named John Yudkin published a study that claimed that sugar, not fat, was the driver of heart disease. As he later wrote in his polemical book Pure, White and Deadly, there was only a modest link in international studies between fat consumption and heart disease. “A better relationship,” he wrote, “turned out to exist between sugar consumption and coronary mortality.” In fact, as he rather presciently pointed out, in the UK the best“fit” was between the number of television and radio sets being bought and deaths from heart attacks. Buying a TV in the 1950s was a sign of growing affluence, but it also pointed towards a lifestyle in which people would spend a lot more time sitting down.

Yudkin’s message about the dangers of sugar were rejected by the anti-fat lobby and he was, in the memorable phrase of one of his colleagues, “pushed under a bus”. A prominent UK scientist denounced his attack on sugar as “nothing more than scientific fraud” and “not only false and misleading but frankly mischievous”.

In 1972 a former cardiologist, Robert Atkins, began pushing a similar message about the dangers of sugar and carbohydrates in Dr Atkins’ Diet Revolution. When he died, hugely overweight and with signs of heart disease, there was considerable glee among the anti-fat lobby. His widow refused to allow an autopsy.

His modern equivalent, Pierre Dukan, hasn’t fared much better. Like Atkins, the Dukan diet is a protein-rich diet that minimises carbohydrates. This year Dukan was struck off the French medical register for, among other things, promoting his diet commercially.

In the Eighties, when the Atkins diet was at the height of its popularity, I first became concerned about my own diet. I was at medical school where, though we were taught a huge amount about a wide range of things, from anatomy to biochemistry, we learnt very little about nutrition. We were, however, assured that Atkins was spouting dangerous nonsense and were warned about the dangers of saturated fat.

I was slim and did a lot of exercise, but like many students I also ate quite a lot of saturated fat in the form of butter, burgers and salami. I have a family history of heart disease and strokes and my father was a recently diagnosed diabetic. It was plainly time to act.

Zealously I persuaded my overweight father to go on a low-fat diet (it didn’t work) and harangued my mother until she switched from eating butter to eating margarine (though I suspect she switched back when I wasn’t around). Beef was replaced by chicken. Coffee came with a dash of skimmed milk. Eggs were avoided. Yoghurt was always low-fat.

So did I become healthier? Well, no. Over the next few decades I put on about two stone, my body fat went up to a blobby 28 per cent, my cholesterol soared and I became a borderline diabetic.

In 2011, while making a documentary for the BBC, I had a body scan and discovered that my internal organs were coated with fat. I was, the consultant told me, a TOFI — thin outside, fat inside.

The trouble was that although I was eating less fat I was now eating far more carbohydrates. If I had switched to a sensible low-GI diet, eating lots more vegetables and grains, then undoubtedly I would have been better off. Instead I was doing what was advised at the time, which was to eat a lot more starchy foods such as pasta and potatoes.

What I hadn’t appreciated is the way these foods act on your body. Eating a boiled potato will push your blood glucose up almost as quickly as eating a tablespoon of sugar. Ironically, if you eat the potato with butter, the fat will slow absorption and the blood sugar peak will be slower and less extreme.

I also hadn’t appreciated that carbohydrates, particularly refined carbohydrates such as rice, potatoes and pasta, are less satiating than fat or protein. You eat them and then a few hours later you are hungry. So you eat some more.

The man who did more than most to convince America, then the rest of the world, then me, to travel the low-fat road, was a physiologist called Ancel Keys. In 1953 Keys published a paper called Atherosclerosis: A problem in newer public health. His paper included a graph comparing fat consumption and deaths from heart disease in men from six different countries. Men in the USA, who got a lot of their calories from fat, were far more likely to die from heart disease than men in Japan who ate little fat. The link seemed straightforward, clear and very compelling.

But Jacob Yerushalmy and Herman Hilleboe — a statistician and the New York State Commissioner of Health respectively — responded with a scathing critique, Fat in the diet and mortality from heart disease: A methodological note. In the measured language of science they tore into Keys, wondering, for example, why he had chosen to focus on just six countries when he had access to data from twenty-two countries. Or, as they put it, “since no information is given by Keys on how or why the six countries were selected, it is necessary to investigate the association between dietary fat and heart disease mortality in all countries for which information is available”.

In other words, it looked very much as if Keys had been cherry-picking his data. If you added in other countries such as France and Germany (countries with high rates of fat consumption but relatively modest rates of heart disease) the link became much weaker.

Yerushalmy and Hilleboe also posed the question: “How does fat (and by extension, animal food variables) relate to other causes of death?” Their answer was that although eating animal fat may lead to more heart disease, you are less likely to die of other things. They could find no link between eating animal fat and increased risk of overall death.

Despite what seems in hindsight to be valid criticisms, the “war on fat” picked up unstoppable momentum. Over the next few decades huge numbers of people cut their consumption of animal fats, like butter and cream. They didn’t, however, start eating lots more healthy stuff. Instead they gorged on sugary carbohydrates and vegetable oils.

Most of those vegetable oils were highly processed. To turn oil into margarine the manufacturers used a process called hydrogenation, which in turn led to the production of trans fats. Trans fats, until recently found in most shop-bought biscuits and cakes, are the Lord Voldemort of the fat world. They are being phased out.

Along with the demonisation of fat, cholesterol also took a beating. If it was common sense that eating fat would clog up your arteries, then it was also common sense that eating cholesterol would do the same. After all it was cholesterol in the arteries that was doing the clogging.

Foods rich in cholesterol, such as eggs, were shunned. Governments warned consumers to eat no more than one egg a week; restaurants pushed the merit of white-only omelettes and supermarkets were stacked to the rafters with foods that declared themselves “cholesterol-free”.

Along with the crowd I gave up eating eggs and tried to persuade the rest of my family to do likewise.

Yet it turned out that the effects of the cholesterol we eat on the cholesterol levels in our blood is relatively small. Even Ancel Keys had concluded in the Fifties that “the cholesterol content of human diets is unimportant in human atherosclerosis”.

It is a myth that has taken a very long time to die. The American Heart Association still issues dire warnings about the dangers of eating cholesterol. Yet a meta-analysis of 17 studies published in the British Medical Journal last year concluded that “higher consumption of eggs is not associated with increased risk of coronary heart disease or stroke”.

I now eat eggs most mornings. When scrambled, boiled, poached or in an omelette, they are a superb source of protein, rich in vitamins and minerals. There are about 90 calories in a boiled egg, half that of a small bowl of Frosties and a quarter that of a croissant with butter and jam. Unlike the cereal or the croissant, the protein in the eggs will keep you feeling fuller for longer.

Another persistent myth about cholesterol is that it is a powerful predictor of heart disease. I’ve recently had my bloods checked and my total cholesterol is higher than it should be, which of course is worrying. Or is it?

My father had a heart attack at about my age so I know I am at risk, but I also know that half the people who are admitted to hospital with signs of heart disease have normal cholesterol levels, while plenty of people with high cholesterol scores will never develop heart disease.

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