Over time, the science on the issue of dietary fat and heart disease has undergone drastic changes, and in particular, advice to eat margarine rather than butter has been reversed. What is the history of this subject?
Throughout most of the 19th century, the commonly held scientific belief about the health impact of dietary fat was that fat, along with protein, tended to prevent obesity, by causing satiety. The best known proponent of this hypothesis was Jean Anthelme Brillat-Savarin, who wrote The Physiology of Taste in 1825. In this period, cardiovascular disease was poorly understood, and public health concerns centered on lack of nutrition among the poor. Because the poor in France often could not afford butter, Napoleon III offered a prize for developing a substitute, and this led to the invention of margarine, which was commercialized ca. 1870.
The early 20th century saw increased scientific and medical interest in cardiovascular disease, which was deadly and untreatable. Coronary artery disease was identified in 1912 by James B. Herrick, who coined the term “heart attack.” In the period before World War II, the focus was on diagnosis and treatment. Diet had not been implicated as a factor in heart disease, and food safety was seen as revolving around preventing the addition of adulterants. Dairy farmers in the U.S. successfully lobbied for the passage of legislation in 30 states to require that margarine be taxed and either sold with its natural gray color or dyed pink as a warning. These restrictions were only gradually eliminated. During World War II, food shortages caused many people to eat margarine rather than butter, and some people continued these eating habits after the war. But margarine continued to carry a stigma, and as late as 1959, a margarine company felt compelled to hire Eleanor Roosevelt to do a TV commercial reducing the stigma associated with margarine.
The central figure in this story, starting around World War II, is the University of Minnesota physiologist Ancel Keys, a colorful and self-promoting figure who developed K rations (the “K” probably stood for “Keys”) and carried out a study, ethically dubious by modern standards, in which conscientious objectors were scientifically studied while they underwent starvation and were then nursed back to health. In 1952, he published the hypothesis that a diet rich in saturated fat caused an increase in blood cholesterol, which in turn led to atherosclerosis. From 1956 to 1978, he carried out his best known project, the Seven Countries Study, which searched for correlations between heart disease and lifestyle factors in the US, Finland, Netherlands, Italy, Yugoslavia, Greece, and Japan. He found that high blood pressure and smoking were correlated with heart disease, and also appeared to verify his hypothesis about saturated fat.
What followed was a rush to judgment by public health officials to discourage the consumption of saturated fat, and in particular to convince people to switch from butter to margarine. In the US, the 1977 McGovern Report recommended that people shift their diets away from fat and toward complex carbohydrates. The only immediate blowback was from farmers whose economic interests would be harmed, as well as from doctors who believed that it was not the proper role of government to advise people about their health. The food industry responded in a variety of ways, including marketing carbohydrate-based foods as low in fat, making reduced-fat versions of dairy products, and producing fat substitutes.
Over the years, it became clear that the evidence on a link between diet and heart disease had always been weak, that the interpretations had been overblown, and that the scientific reality was both difficult to probe methodologically and extremely complicated (e.g., it took decades before “good” and “bad” cholesterol were distinguished, and for researchers to realize that bad cholesterol comes in a variety of particle sizes). The Seven Countries Study was criticized on a variety of methodological grounds, such as possible cherry-picking of the countries. Even studies that support a link between fat consumption and heart disease don't show a clear effect on mortality. In fact, one of Keys's own large studies, from institutionalized mental patients in the 1970s, was never published until 2016, probably because it appeared to show that patients put on a cholesterol-lowering diet were more likely to die from heart disease. One very large study, the Women's Health Initiative, found no difference in heart disease among women who changed their diets in ways that lowered their “bad” cholesterol.
In retrospect, this episode in scientific history appears to be a demonstration of confirmation bias and the formation of alliances between scientists, government, and industry to promote a premature scientific consensus. Researcher Dariush Mozaffarian says, "In the nutrition field, it's very difficult to get something published that goes against established dogma. The dogma says that saturated fat is harmful, but that is not based, to me, on unequivocal evidence."