I’ve been taught since my undergraduate days in medical college that eating saturated fats was to ask for trouble. Meat (red or white), cheese, butter and egg yolk were prohibited. Repeated guidelines from the American Heart Association (AHA), the American College of Cardiology and even the World Health Organisation were clear that fats in general, and saturated fats in particular, were to be strictly avoided to prevent a heart attack. The message was to reduce fats to less than 30% of the total calories consumed in a day, and with saturated fats to be kept well below 10%. Why, most people on the planet followed these dietary commandments from the two most powerful and respected cardiology associations.
The AHA declared in 1961 that saturated fats were bad because they increased blood cholesterol, which blocked coronary arteries and caused heart attacks. Surprisingly, the AHA was driven this conclusion by the hypothesis of one physiologist who didn’t bother to submit a shred of evidence. Ancel Benjamin Keys, a physiologist with a PhD from Cambridge University, stamped his ‘diet heart’ hypothesis into the consciousness of Paul Dudley White, a founder-member of the AHA. White was attending to Dwight Eisenhower, then the US president, who suffered his first heart attack in September 1955. Many middle aged Americans were succumbing to heart attacks in the 1950s and the situation demanded convincing answers from the health community. Eisenhower had helmed NATO and, before that, had been the supreme commander of the Allied forces that wrenched Europe back Europe from the Nazis.
Eisenhower managed the brilliant generals George Patton and Bernard Montgomery, and famously warned the American public in his farewell address of the “military-industrial complex”. But as president, he had no clue of the new and rapidly developing “health-pharmaceutical-industrial complex.”
Keys was able to launch his ‘diet heart’ hypothesis because there was little science available in the 1950s that could explain the near-epidemic heart attack among middle-aged Americans. He presented his “seven countries study” that displayed a clear association between eating greater amounts of saturated fats and deaths due to heart disease. The seven countries were the US, Japan, Yugoslavia, Netherlands, Italy, Greece and Finland. The method behind the study was seriously flawed, however.
The biggest was that Keys had cherry-picked these countries because they supported his hypothesis. He left out 15 countries that did not reveal any association between saturated-fat consumption and heart mortality. He conveniently ignored Denmark, Sweden and Norway, each of which had relatively few deaths from heart attacks in spite of sporting diets with lots of saturated fats. And Chile, on the other hand, had a high cardiac mortality despite eating little saturated fats. An unbiased investigator would have realised these problems in Keys’ hypothesis – as they do now – but didn’t: they hadn’t been presented with the complete data.
Keys also checked food samples for fats in less than 4% of the 12,000 participants he studied, and when the food was studied it was checked for a single day among the American and for less than a week among the European participants. Keys had been impressed by the large number of long-lived people on the Greek island of Crete, but had tested them when they’d been fasting for more than a month during a religious festival. In this period, more than 60% of the population abstained from meat, butter and cheese. This led Keys to the wrong conclusion that a low-fat diet was the key to longevity.
The AHA was so impressed by the ‘diet heart’ hypothesis that it made an official policy of it, and voila! By 1977, more than 220 million Americans were being urged by the US government to adhere to a low-fat diet. The British, true to form, officially imposed the same diet guidelines by 1984 on their subjects.
Remarkably, the AHA ignored no fewer than six randomised studies – including almost 2,500 heart patients – that showed no difference in mortality between the intervention group (low saturated-fat diet) and the control group (which continued with its regular eating habits). Both the intervention and control cohorts had 370 deaths each. Moreover, no women were being studied, and in the absence of a single primary prevention trial, the AHA and the US government had formulated their advisories.
The food industry also got in on the action. Vegetable oils started being manufactured in the millions of tons. Leading them all was Procter and Gamble, which began to aggressively market cottonseed oil – as well as make a sizeable donation to the AHA, an amount worth $20 million today. The corresponding “diet-food-health-industrial complex” has not looked back in the 60 years since.
The largest randomised trial assessing the effects of a low-fat diet on heart and cardiovascular diseases was the Women’s Health Initiative. It followed up 49,000 postmenopausal women who had been on a low-fat diet (alongside an increased intake of fruits, vegetables and grains) for eight years but had failed to lower their risks of death, heart attack, stroke or diabetes.
Two large reviews and meta-analyses (this and this) involving more than 600,000 participants have also failed to show any reduction in cardiovascular events, or death, by replacing saturated fats with vegetable oils. There was an increase in cardiovascular events due to trans-fats.
The Minnesota, DIRECT, Framingham and PURE studies
In 1967-1973, doctors intervened in the diets of a group of people randomly picked from a cohort of 9,000 for the famous Minnesota Coronary Experiment. The intervened group had saturated fats replaced by a polyunsaturated vegetable oil. The control group continued with their regular American diet. These people were from enrolled from mental institutions and from homes for the elderly. More than 2,500 participants continued on their respective diets for at least a year, and autopsy reports were available for about 140 deaths. This trial’s results were never published until a group of investigators got its hands on all the raw data.
They were dumbstruck to learn that the autopsies revealed 42% of the people in the intervention group had suffered a heart attack against only 22% in the control group. Both groups had similar amounts of atherosclerosis in their coronary arteries.
The other major finding was that, in spite of a 13% reduction in blood cholesterol with a vegetable-oil diet, there was a paradoxical 30% higher mortality in people older than 65 years. To explain this, the investigators hypothesised that the lowered cholesterol had the denser LDL particles that are oxidised more easily and so invade the coronary faster. As it happened, the principal investigator of the Minnesota Coronary Experiment was none other than Ancel Keys.
The other distinct possibility (to explain the mortality paradox) is that polyunsaturated vegetable oils produce hundreds of oxidised molecules that are toxic to the human body. For example, the aldehydes are carcinogenic apart from being able to compromise cognition. Another randomised trial assessing the replacement of saturated fats by corn oil also showed an increased mortality against the control group.
More recently, the DIRECT trial finished up in Israel in 2008. It divided participants into three groups. The first was kept on a low-fat diet; the second, a Mediterranean diet; and the third, a low-carbohydrate high-fat diet. At the end of follow-up period, the low carbohydrate high fat group was found to have lost the most weight, have the highest levels of HDL (a.k.a., ‘good cholesterol’) and have triglyceride levels lower than the high-fat group. In fact, the low-carbohydrate high-fat group also had better metabolic markers across the board.
The Framingham study, which began in 1948 and still continues, has been following the consumption of dietary fats and the development of heart disease among its 5000+ inhabitants, chosen from Framingham, Massachusetts. At the end of the first follow-up, the investigators were unable to find any correlation between fat-intake, cholesterol and heart disease.
But like with the Minnesota Coronary Experiment, the data was never deliberately published. In William Kannel, who served as the study’s the chief investigator in 1969-1979, at one point even stated: “That blood cholesterol is somehow intimately related to coronary atherosclerosis is no longer subject to reasonable doubt.” After a 30-year follow-up, the study reported that 1 mg% per year reduction in cholesterol was associated with 14% increased cardiovascular mortality and 11% total mortality.
Finally: the Prospective Urban and Rural Epidemiological (PURE) survey examined cardiovascular risk factors around the world in 2003-2009, with more than 150,000 participants. Though the results are yet to be published, a recently leaked (and now unavailable) video stated that there seemed to be no correlation between saturated fats (red meat, white meat, dairy products) and heart disease but a positive correlation between carbohydrates and heart disease. Moreover, a very sensitive cardiac-risk-factor marker was found to have increased with carbohydrates and reduced by saturated fats. Vegetables and fruits had no effect on the marker.
Though the PURE trial was very large, it was an observational that, strictly speaking, can’t explain causality.
So, based on the evidence obtained from well-conducted clinical trials, Keys’s ‘diet heart’ hypothesis is wrong. However, it remains to be seen when the big cardiac bureaucracies will begin to edit their guidelines. The ‘big cholesterol is bad’ maxim remains firmly in place because its persistence allows drugmakers to persist with large profit margins on drugs that may not even be necessary. Precisely this was confirmed by the FOURIER trial presented in the American College of Cardiology Meeting held in March 2017.
FOURIER was a ‘mega-trial’ that randomised 28,000 cardiac patients to a statin-plus-evelocumab versus a only-statins for two years. The annual cost of an evelocumab regime is $14,000 (Rs 9 lakh). In the end, LDL cholesterol levels had plunged to about 30 mg% in the evelocumab group versus about 90 mg in the only-statins group. There was also a 1.5% absolute reduction in stroke and myocardial infarction risks but – get this – no reduction in mortality. Implication: 75 patients will need to be treated for two years to prevent a single heart attack or stroke, at a total cost of Rs 13.5 crore. You’re likely to get a better deal without spending a penny by following the Copenhagen study: 10 minutes of slow-jogging per day reduced mortality by 70% compared to being sedentary the whole day.
It’s difficult to not feel dizzy when confronted by organisations like the AHA and the WHO, which have converted hypotheses into dogma etched on stone without any evidence in the past. But what then would be good and sane dietary advice to a layperson? There has to be an application of common-sense, a request to continue to eat fruits, vegetables, whole grains and nuts. At the same time, there is no need to stay away from meat, butter, cheese and eggs. There is no evidence that eating saturated fats along with reasonable amounts of proteins, with about 45% of calories as carbohydrates will, trigger a heart attack. Au contraire: evidence has emerged that increasing carbohydrates to 55% or more can actually be harmful to the heart. Even the current obesity epidemic and type-2 diabetes are most likely the handiwork of an increased carbohydrate intake that has replaced fats in people’s diets.
Deepak Natarajan is a cardiologist based in New Delhi.