Low fat diets: Not fit for purpose

I was told recently that food bills in Thailand are rising because health-conscious Thais had started buying expensive bottles of polyunsaturated oil, rather than the cheap coconut oil they'd used for millennia. The reason? Polyunsaturates fitted the low-fat mantra while coconut oil, high in saturated fat, was now bad. I felt like banging my head on the dashboard.

It's head-banging stuff because the story encapsulates just how simplistic and wrong this 30-year-old public health dogma is. It all dates back to a US Senate committee, headed by George McGovern in 1977, that produced a report advising a low fat-policy as a way of cutting heart disease, on very little evidence. For details on just how little and why, even so, it rapidly became established as official policy, see American science writer Gary Taubes's brilliant book The Diet Delusion.

What's remarkable is how tenaciously this simplistic theory has persisted, despite constantly being tested and found wanting. Not only is it now disrupting perfectly healthy traditional eating practices worldwide, but there's good evidence to suggest it has actually contributed to the current obesity and diabetes epidemics.

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Like all successful dogmas, political or religious, the success of the low-fat theory depends partly on suppressing opposing theories and data. You're unlikely to have heard much about the contrary evidence. For decades, a costly research programme has been under way to prove the low-fat theory; what's remarkable is just how many good, large-scale studies directly contradict it.

For instance, 10 years after the McGovern report, the American surgeon general's office began a study to collate all the evidence for the low fat/reduced heart disease link. It was never published. Eleven years later, it was terminated because it had required "too many staff". If it had come up with anything very convincing you can be sure you would have heard about it.

Then in 2000, a group of scientists called the Cochrane Collaboration analysed 27 of the most rigorously controlled studies involving more than 18,000 participants and found that diets low in saturated fats have no significant effect on mortality, or even on deaths due to heart attacks. Two years ago came the Women's Health Initiative trial involving 20,000 women over eight years, which found that a diet low in total fat and saturated fat had no impact in reducing heart disease or weight.

Just how effective has the policy of cutting fat been in lowering obesity and heart disease? The rise in obesity in America, followed by the UK, began in the early Eighties, a few years after the low-fat policy became official. For the previous 20 years, obesity levels had been fairly constant. Since then, Americans and the British have been eating less fat than ever and yet we are also fatter than ever and diabetes rates are soaring.

You are unlikely to have been given any information about the complexities and benefits of fat. Thais and millions of others in Asia and the Pacific have traditionally used coconut oil and we know that, until the arrival of a Western diet, they had little problem with obesity or heart disease. Ethnic groups such as the Masai and Inuit are famous examples of how you can stay slim and heart-attack free on very high fat diets. Can something that has always been a valued part of the human diet suddenly turn hostile?

Saturated fat isn't just a bad thing, it's an essential part of our physiology; we need it to absorb vitamins; it's vital for the immune system and it's complicated stuff. It comes in several forms; the main one in coconut oil being lauric acid, which is a component of human milk, and valuable for fighting off bacterial infections. Another component of saturated fat is stearic acid, which gets turned into a monounsaturated acid in the body – the same one that makes up healthy olive oil.

And there's another way of looking at so-called "healthy" polyunsaturated oil, too. Items on a long charge sheet include harming the immune system and the liver, accelerating ageing and causing poorer mental functioning in animals under stress.

The low-fat-is-healthy dogma is shored up by ignoring its shaky foundations and an alternative explanation of why diabetes and obesity is rising. For years, the fat establishment ignored experts such as Dr Robert Atkins who pointed out the role of carbohydrates in weight gain and damage to arteries, especially refined carbohydrates.

The explanation goes like this. When you cut out fat, you tend to consume more refined carbohydrates – usually as sugar. It is possible to eat an officially "healthy, balanced diet" and have the equivalent of 60 teaspoons of sugar a day because all carbohydrates are turned into blood sugar and this diet encourages you to have a lot of them.

Regularly raising your blood sugar in this way is dangerous because it increases the amount of insulin you produce to clear it away. Not only does insulin lead to excess sugar being stored as saturated fat, but increased amounts of insulin can have a number of harmful effects, such as raising cholesterol, blood pressure and damaging the lining of arteries.

Already, studies are suggesting that this could be a more accurate picture of what is going on than the low-fat model. One was published last year by researchers at the University of Connecticut. It compared the effects of a high-fat and a low-fat diet on fats in the blood (triglycerides). Those in the high-fat group had better cholesterol levels triglycerides lowered by 51 per cent, versus 19 per cent.

The simplistic notion that eating a low-fat diet would help with weight loss because it contains fewer calories doesn't begin to describe the complexities of weight control. What's more, all sorts of other factors from stress to vitamin D are now emerging as playing a role in heart-disease risk. The low-fat diet is simply not fit for purpose.