A brief history.
Eat less saturated fat. This slogan, along with others like it, has been pressed on us by nutritional authorities over the past 50 years or so. At a population level we largely listened and modified our behaviour. Meanwhile, obesity and other ‘diseases of civilisation’ steadily increased. Objectively, the message has been a failure and, disturbingly, it may have done us harm. The science does not support the message, and never has.
The history is revealing
Dr Ancel Keys (1904–2004) was an American epidemiologist who was interested in the effects of diet on health. During World War II, Keys developed the K-ration given to soldiers in the field (the ‘K’ was no coincidence), and studied starvation and recovery in conscientious objectors (inhuman experiments without the nuisance of ethics committees). He was described as ‘confident’.
Keys’ starvation work led him to travel to the post-war Mediterranean where heart disease appeared to have declined with reduced food availability. He ended up concluding that it was a reduction in animal fats that gave protection from heart disease. He didn’t just think that animal fats might be associated with heart disease, he considered them a cause. It wasn’t his original hypothesis though — originally he thought that diets high in cholesterol were to blame. However, he learned that the level of cholesterol in the blood had no relationship to the amount in the diet and therefore that dietary intake was not relevant. But he was aware that dietary saturated fat could raise blood cholesterol, and so that became his target.
He compiled heart disease and saturated fat consumption data from 7 countries in northern and southern Europe, the USA and Japan and used it to show an increase in heart disease with an increase in fat consumption. He used this for his campaign.
However, there was data available to him from another 22 countries, not just those ones. He left that bit out. If they had been included, the relationship would have been unconvincing (a recent study of 18 countries from 5 continents indicates that higher saturated fat consumption associates with lower mortality). From the outset, his campaign was a fraud.
However, at the time, white middle-aged male politicians were getting increasingly alarmed by the sudden rise in heart disease in the American population. They wanted someone to tell them what to do about it.
Although Keys was claiming he had the answer, his work was criticised by fellow scientists from the outset (not that that meant he was wrong). Preliminary studies were not showing a benefit in low fat diets, and they worried that fat was an essential macronutrient that the body needed to function properly (e.g. after water, fat makes up 70% of the brain). They cautioned that restricting dietary fat could be dangerous. In 1957, the American Heart Association (AHA) refused to endorse reducing saturated fat in the American diet.
Then, in 1961, the AHA did an about-face and recommended a low fat-high carbohydrate diet for Americans at risk of heart disease (not for the general public).
Two things had changed. First, a study (the Framingham study) was published providing evidence that blood cholesterol associated (albeit weakly) with heart disease (an association that subsequently disappeared with longer followup). But, the second was perhaps more important: Ancel Keys was elected to the board of the AHA. The two events got Keys on the cover of Time magazine.
The fate of fat was settled, it had met its nemesis. The AHA bowed to political pressure to do something about the rise in heart disease, Keys was a powerful and uncompromising individual with new authority, there was a study that appeared on-message and finally, the message was nice and simple and the popular press welcomed it and the public got it.
So that’s how it all started. Biased analysis by a charismatic individual, influence, political pressure, manipulation and media support set up a nutritional message that persists today.
A brief history of the intervening years — the search for evidence and the birth of dietary guidelines:
The AHA recommends that people at risk of heart disease limit total fat intake to 30% of calories (10% saturated; 20% unsaturated). To keep some perspective, Keys himself only recommended limiting carving meats (roasts etc) to 3 times a week.
The National Institutes of Health sets up a Diet Review Panel of experts in epidemiology, statistics, nutrition and clinical medicine to review the evidence for the hypothesis that saturated fat increases the risk of heart disease. They find that the available evidence does not support the hypothesis and, furthermore, express concerns that reducing fat intake could have adverse consequences.
Around this time, two randomised controlled studies (Minnesota coronary study, Sydney heart study) found that replacing saturated fat with polyunsaturated oils increased mortality. Neither study was published by the authors (the studies were expected to confirm the hypothesis) but the results were archived. The archives were uncovered in the 2010s and the findings published independently (without making an impact).
A Select Committee on Nutrition and Human Needs ponders the recommendation for dietary fat to be included in the upcoming ‘US Dietary Goals’. This highly-contentious committee, comprising mostly non-experts in the field and written by a vegan junior staffer without a scientific background, recommends extending the AHA guidelines (until then for people at risk of heart disease) to the entire American adult public.
This causes a furor in the scientific community. Even the American Medical Association protests.
Subsequent campaigns by scientists to have the recommendation overturned put the scientists apparently on the same side as the dairy and beef industries and so discredit them by association. Even an organisation as prestigious as the National Academy of Sciences doesn’t escape. The Academy directs its Food and Nutrition Board to provide a science-based assessment of the current position. The Board concludes: just watch your weight — everything else will take care of itself.
The Select Committee don’t take the Board’s conclusion well. Not only does it reject their recommendation, it undermines their own relevance. The Board becomes the subject of a determined public campaign accusing it of being an industry apologist and having industry links. The media frenzy eventually succeeds in obscuring the science and discrediting the Board and its findings.
The US Department of Agriculture (USDA), the government body with the last word on the matter, then takes up the saturated fat message and begins putting the recommendations into practice throughout the US.
A series of well-controlled saturated fat studies are published that consistently find no link to heart disease.
The results from the Coronary Primary Prevention Trial are published, confirming the Framingham study by showing a weak association between blood levels of cholesterol and heart disease. This triggers a renewed public campaign, another cover on Time magazine, and the extension of the AHA guidelines to every American over the age of 2 years (regardless of anything else).
The US Surgeon General’s Office commissions what it hopes will be the definitive report linking saturated fat to cholesterol and heart disease. The task is to compile the science and get it reviewed by an expert committee who would issue a proclamation. The committee is tasked with supporting the hypothesis that saturated fat increases the risk of heart disease (it is not required to compare the scientific data for or against the hypothesis). It takes longer than expected (see 1999).
A disturbing turn of events. Data starts to appear showing that low levels of dietary saturated fat might be associated with other mortalities such as cancer and respiratory illness. A troubling finding was an increased likelihood of death by accident and trauma — the brain might have gone into a high-risk survival mode. The fears that dietary advice could do harm were realised — not surprisingly, fat had a bigger role to play in our biology than just the heart. The authorities do nothing — they ignore the most fundamental principle in medicine — do no harm.
It has now been eleven years since the US Surgeon General’s Office committee was convened (in 1988). They give up. In the face of the complexity of the task and the simple fact that the science was not supporting the hypothesis, the committee quietly admits defeat and disbands without fanfare.
Large meta-analyses of prospective (stage 3) studies appear in the following decade. The conclusion remains the same — despite decades of research effort and who knows how many hundreds of millions in precious research dollars, it is still not possible to definitively show that saturated fat has any significant part to play in heart disease.
This should come as no surprise. Given the diet that our species evolved with, it is impossible that our biology would have penalised us for eating animal fat.
Our diet has been experimented on at a national level with an hypothesis that started out as a campaign by a relentlessly ambitious individual, that went on to become lore, that didn’t and doesn’t have scientific backing, and that is likely to be harmful to our health.
The Gary Taubes article was highly influential when published in 2001: The soft science of dietary fat
The definitive book by Nina Teicholtz: A big fat surprise
An update by J Elliott in 2014: Flaws, fallacies and facts: Reviewing the early history of the lipid hypothesis
Minnesota Coronary Study: https://www.bmj.com/content/bmj/353/bmj.i1246.full.pdf
Sydney Heart Study: https://www.bmj.com/content/bmj/346/bmj.e8707.full.pdf
A British Medical Journal (BMJ) blistering editorial on the fallacy of the saturated fat guidelines.
Scientists are now questioning the value of nutritional advice and the minimum level of evidence needed before issuing it: A call for higher standards of evidence for nutritional guidelines.