Besides restricting fat for weight loss, the scientific community embraced and stridently promoted
another hypothesis: that fat root heart disease, our biggest killer. But the history of medicine is full
of good ideas that turned out to be wrong and even high risk. Thalidomide seemed to be a great idea
and very effective at preventing morning sickness in pregnancy until it was discovered to cause
severe birth defects. Hormone replacement therapy for women was thought to be so effective in
preventing heart disease in women that it was considered malpractice not to prescribe it. More than
fifty million menopausal women happily took hormones until a large study sponsored by the National
Institutes of Health found that hormone replacement actually increased the risk of heart disease,
stroke, and breast cancer.
Before you read any further, you need to know the truth: Eating saturated fat does not cause heart disease. We know this might seem startling, given that we have spent the better part of a century avoiding everything from butter to egg yolks because we were told they were not good for our hearts. But better to know the truth and make new and healthier habits going forward.
The theory that fat, and specifically saturated fat, is the cause of heart disease all started because
of two main findings. First was that rabbits (which are obviously very different from humans)
developed atherosclerosis (fatty deposits in the arteries) when they were fed cholesterol, which is
completely absent from their vegetable diet. Second, countries that seemed to consume more saturated
fat and the most fat generally (for example, Finland and the United States compared to Japan and
Greece) had more heart disease. Since saturated fat raised blood levels of cholesterol, it was
supposed that saturated fat caused heart disease. Suddenly, a weak hypothesis that was based on shaky observations, not on any real experiments, was taken as fact.
This idea, spawned in 1953, was the brainchild of a very outspoken, passionate scientist from the
University of Minnesota named Ancel Keys. Many questioned Keys’ scientific conclusions, but he
was vigorous in the faults of anyone who challenged him. He was a dominant, persuasive, and
charismatic man who convinced the world of his hypothesis.
The history and failure of Keys’ diet-heart hypothesis, that fat is bad, is well documented in Nina
Teicholz’s book, The Big Fat Surprise. Keys made his conclusions based on observations of heart
disease, death rates, and fat consumption in six countries, even though data on twenty-two countries
from the Food and Agriculture Organization of the United Nations U.N and data from the World Health
Organization (WHO) was available. The diet record keeping was questionable. He selected 6
countries that he felt had the best data (or perhaps that he knew would best support his ideas) and
found a direct correlation between the amount of fat in the diet and heart disease. He ignored data
from the other sixteen countries. A more recent 2010 review by the Food and Agriculture
Organization found that “there is no likely or convincing evidence” that a high fat diet causes heart
Yet despite that fact, and the fact that observational or population studies cannot prove cause and effect, Keys’ study took hold. Dr. Keys followed up his six countries study with the famous Seven Countries Study, launched in 1956, in which he again carefully selected countries that supported his theory and conveniently omitted countries such as France and Switzerland that had high-fat diets and very little heart disease. He followed 12,770 people but evaluated diet intake for only 499, or 3.9 percent of them. This is poor science, insufficient to make broad conclusions. Yet draw “definitive” conclusions he did, and he further refined his theory to focus on saturated fat as the enemy.
The theory went something like this: Blood cholesterol was associated with (but not proven to be
a factor in) increased risk of heart disease. Saturated fats increased cholesterol. So the enemy was
saturated fat. While he did find a correlation between saturated fat and heart disease in the countries
he picked, he did not find any reduction in death in countries with lower saturated fat intake. And
though he found the correlation of saturated fat and heart disease between countries. When he looked
at different regions of the same country, such as different regions of Finland or different islands in
Greece, such as Corfu and Crete. he found that they had widely different rates of heart disease.
Something didn’t add up.
There were many problems with Keys’ research, including the way in which he collected people’s
dietary history and how few people he had dietary information on for a population-type study, which
usually requires thousands of participants to be able to draw any conclusions. He studied countries in
postwar Europe, when diets were affected by wartime shortages, so they didn’t represent the true
diets of these populations. And there were many other severe limitations in his research. Basically, he
set up his study to prove his hypothesis.