Bad Science: How We Came to Demonize Saturated Fat

 "The great enemy of truth is very often not the lie—deliberate, contrived and dishonest—but the myth—persistent, persuasive and unrealistic. Too often we hold fast to the cliches of our forebears. We subject all facts to a prefabricated set of interpretations. We enjoy the comfort of opinion without the discomfort of thought."

JFK, Yale University (1962)

For half a century we were told to be terrified of saturated fat and cholesterol. It would coat the inside of our arteries like gunk in old pipes and give us heart attacks, strokes, diabetes and everything else bad in the world. To protect ourselves against this scourge, the nutrition authorities recommended we cut out as much dietary fat as possibleespecially animal fatand replace it with carbohydrates.

Yet there’s absolutely no scientific evidence linking dietary fat and cardiovascular health. Never has been. As a recent study in American Journal of Clinical Nutrition puts it, “there is no significant evidence for concluding that dietary saturated fat is associated with an increased risk of CHD or CVD.”1 As the FAO and the WHO reported: “The available evidence from cohort and randomized controlled trials is unsatisfactory and unreliable to make judgment about and substantiate the effects of dietary fat on risk of CHD.”2 Even the USDA, after decades of shouting from the rooftop that dietary cholesterol leads to heart disease, quietly removed dietary cholesterol from its list of ingredients of concern in 2014.3

How did the baseless recommendation to cut fat and increase carbs persist for over 70 years without even a shred of evidence? Why do so many people today still avoid saturated fat and cholesterol despite the fact that even the official nutrition establishment no longer tells them to do so? In this entry, I put on my history-nerd hat and trace the genealogy of the most pernicious health screw-up of our generation. It’s long, it’s messy, but it’s also a valuable case study in cognitive biases and the dangers of delegating critical decisions to “the experts”, especially when it comes to something as fundamental as our health


Ancel Keys

It all started in the middle of the 20th century when gifted scientist, fellow Coloradan and one-time guano shoveller Ancel Keys got his hands on the latest medical gadget of his time: A blood-cholesterol monitor. Researchers had just discovered how to measure this particle and Keys, a physiologist at the University of Minnesota at the time, took up the new technique with gusto. He would use it to change the course of public health over the next 70 years.

Keys was mostly interested in nailing the culprit behind the rash of heart attacks killing businessmen across the United States. Although the heart attacks were probably the result of increased Mad Men-style smoking, Keys conveniently formulated his hypothesis around the object he had just learned to measure—cholesterol. After testing 268 businessmen with the new technique and finding elevated levels of cholesterol in their blood, Keys decided that he had found his culprit. Keys then made an even more fateful, heroic and ultimately notorious leap of logic, concluding that this fat in the blood was caused by fat in the diet.

Armed with his shiny new cholesterol-measuring apparatus and his simple, persuasive hypothesis, Keys traveled to Europe in search of supporting evidence. With his wife as assistant, Keys took blood cholesterol samples and dietary information from two groups of Italians—poor workers, and the wealth elite. He found exactly what he was looking for: The wealthy, who suffered more heart attacks, also ate fattier diets and had serum cholesterol levels as high as those of the businessmen Keys had worked with back home. The workers, relatively unplagued by cardiovascular disease, ate diets with less fat and had significantly lower levels of cholesterol in their blood.

Of course, the workers also ate less sugar than the rich folks did and spent most of their time outside doing physical labor, but Keys wasn’t exploring hypotheseshe was gathering evidence. Keys presented his conclusion at a WHO conference in Amsterdam in 1952: A fatty diet, he stated, raised serum cholesterol and led to atherosclerosis, thereby raising the risk of myocardial infarction.4

As simplistic explanations often do, Keys' hypothesis that fat in the diet led to fat in the blood seemed reasonable, and it resonated with a large audience. It was easy to visualize the grease from your cheeseburger seeping into your veins and accumulating into gunky plaques. Even the president of the International Society of Cardiology, Dr. Paul Dudley White, jumped on Keys’ bandwagon. No one in Keys’ camp seemed concerned that the two groups of Italians on which their entire premise was based had a million other differences aside from just fat consumption.

The press went to town. Newsweek ran a feature titled “Fat's the Villain”5 and the New York Times published an especially sensational article claiming that experts “agreed that high-fat diets, which are characteristic of rich nations, may be the scourge of Western civilization. The diets were linked with hardening and degeneration of the arteries.”5

The discussion turned truly national when President Eisenhower suffered a heart attack in 1955 (he would spend the remainder of his life eating melba toast and grapefruit). Throughout the press conferences following the president's illness, White repeatedly warned Americans against the dangers of dietary fat. Stress didn't cause the president's heart attack, he wrote in a nationally-published newspaper article, artery-clogging plaque did. The day after White's article hit the press, Keys showed up on the cover of Time magazine repeating his claim that atherosclerosis was the true culprit behind heart disease and that dietary fat caused atherosclerosis.5 It’s as if there’s data we’re not seeing, but there’s notit’s still just the cursory survey Keys did of the Italians.

In 1957 Keys published his famous five-country study (later morphed into the seven-country study), a classic piece of observational epidemiology which would unfortunately become a template for later nutritional research. Keys compared populations in five countries with known disparities in saturated fat consumption, measuring serum cholesterol levels and recording information on cardiac mortality. The results were unsurprising: Like with the Italians, Keys again found a connection between dietary fat, serum cholesterol and heart attacks. Blatantly disregarding the difference between correlation and causation, Keys effused that “each new research adds detail, reduces areas of uncertainty, and, so far, provides further reason to believe.”6

Keys was overwhelmed by his own confirmation bias. When confronted with studies done on populations that ate high-fat diets but did not exhibit heart disease—those done on Benedictine and Trappist monks, Navajo Indians, Irish immigrants to Boston, Swiss alpine farmers, the Masai and other African pastoralists, for example—Keys rejected them as having “no relevance to diet-cholesterol-CHD relationships in other populations”.6

By 1960, Ancel Keys had convinced a significant number of people that fat in the diet led to fat in the blood, which in turn led to the diseases of civilization. The image of plaque-coated arteries was compelling and easy to follow, .

And that's how it began: A shiny new medical gadget, a proselytizing researcher and a casual survey of a few Italians. Once the media jumped on board reporting Keys' simple, intuitive explanation as the new gospel of "the experts", the train had thoroughly left the station.

Yet many scientists still weren’t convinced. Throughout the next decade, Keys and his opponents would engage in a fierce debate over the root cause of heart disease: The Cholesterol Wars (coming soon).



1. Meta-analysis of prospective cohort studies evaluating the association of saturated fat with cardiovascular disease. Siri-Tarino PW, Sun Q, Hu FB, Krauss RM Am J Clin Nutr. 2010 Mar; 91(3):535-46.

2. Reduced or modified dietary fat for preventing cardiovascular disease. Cochrane Database Syst Revon page CD002137. 2009.

3. Food and Nutrient Intakes, and Health: Current Status and Trends. 2014. https://health.gov/dietaryguidelines/2015-BINDER/meeting7/docs/DGAC-Meeting-7-SC-1.pdf

4. Keys, A. “The relation in man between cholesterol levels in the diet and in the blood.” Science. 1950 Jul 21; 112(2899):79-81.

5. Levenstein, Harvey A. Fear of Food: A History of Why We Worry about What We Eat. Chicago: U of Chicago, 2012.

6. Attia, Peter. “The Limits of Scientific Evidence and the Ethics of Dietary Guidelines.” www.eatingacademy.com, 2002.


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