Many experts agree that 1980s fat guidance did not have robust evidence to underpin it, but most of them disagree that it is time to rip it up
Forty years ago butter suddenly became bad for you and those who ate quantities of red meat were taking their lives in their hands. The public response to guidelines advising us to eat less fat smacked of hysteria. The panic was fuelled by the sort of over-simplistic newspaper articles that often follow new guidance on our eating habits. Fat was the root of all evil in the 70s and 80s. Now it is sugar.
A new paper says the guidance on fat should never have been introduced because it was based on poor evidence. Meat and dairy can go back on the shopping list and the dinner table, it implies. The paper, published in the journal Open Heart, is by Zoe Harcombe, an obesity blogger and writer of diet books from the Institute of Clinical Exercise and Health Science at the University of the West of Scotland, and colleagues.
People who ate higher fat diets in trials in the 70s did not have higher death rates from heart disease, they say. Their accusation is that this drive to cut fat let in sugar instead. Carbohydrate consumption went up as fat went down. Food companies went into overdrive to produce low-fat ranges and many products, like the low-fat yoghurts, compensated for the loss of taste by adding large amounts of sugar.
The rise of sugar in response to the fat phobia is undoubtedly real and has done a lot of damage. But while scientists and nutrition experts agree with Harcombe and colleagues that the fat guidance did not have robust evidence to underpin it, most of them strongly disagree that it is time to rip it up.
If the original trial evidence was weak, they say, that is partly because diet and nutrition trials are incredibly hard to do. People often either actually forget what they have eaten in the course of a week or month or suffer from a sort of embarrassment-induced amnesia. They are a bit ashamed of the doughnuts, the crisps and the cream cakes.
The six small studies Harcombe and colleagues looked at from the 70s were randomised control trials - where one group eats what they like and others eat what they are told to.
It is the gold standard model in drug trials, but it does not work well in diets. Patients in a trial will take the pills the doctor gives them. People in diet studies, told not to eat fat, may try and even succeed to a degree, but experience shows that most people revert to their usual eating habits. But they may not want to tell the researchers that they failed.
So nutrition guidelines are not just based on trials. The vast majority are based on epidemiological data - studying trends in large populations.
"It's true that epidemiology studies can be tricky to interpret, and that correlation does not always mean causation," said Prof Richard Mithen, acting director of the Institute of Food Research, "but in reality it is very challenging to design and carry out randomised controlled trials that are big enough and powerful enough to determine effects that are relevant at the whole population scale. Food is more complex than drugs."
Prof Tom Sanders, emeritus professor of nutrition and dietetics at King's College London, said the low-fat guidance was a pragmatic move.
"In the 1970-80s, the UK and other western countries were facing an epidemic of coronary heart disease and there was overwhelming evidence that this was caused by cigarette smoking, especially in the presence of high blood cholesterol.
"It was effectively a policy choice between sitting on the fence and doing nothing or opting to follow what the evidence suggested - that cutting total fat intake would help prevent obesity and reducing saturated fat would lower blood cholesterol," he said.
Anyway, he added, it seems to have worked out OK. "Cardiovascular disease rates have fallen in the UK and other countries that adopted the policy of reducing total fat and partially replacing saturated with polyunsaturated fatty acids: in the UK, total fat has fallen from 42% to 35%, energy and saturated fat from 20% to 12% energy; between 1997 and 2007/8 cardiovascular disease mortality under the age of 75 years fell by 55%," he said.
In the end, said some of the critics, focusing on one nutrient or another is not useful. It is not whether we should eat butter or give up sugar that matters. The best approach is to eat wholesome real food, such as a Mediterranean diet, which includes fruit and vegetables, fish, lean meat and olive oil.
"This review reminds us that, like Saturday Night Fever, tartan culottes and bubble perms, the reductionist 'single nutrient' dietary recommendations deserve to be left in the early 80s where they belong," remarked Catherine Collins, principal dietitian at St George's hospital NHS trust. "As do doctors and other health professionals who persist in their persecution of single nutrients whilst ignoring a 'whole diet' approach."
In the end, said some of the critics, focusing on one nutrient, such as fat or sugar, is not useful. Photograph: Steve Parsons/PA
