The low-fat diet has been widely popular for the past 50 years and for much of that time it was the default diet advocated by most health practitioners. For a time, the consensus was that a diet had to be low in fat to be healthy, especially for cardiovascular health. With the increasing number of studies, our understanding of the effects of dietary fat has shifted and the scientific consensus is beginning to change.
The low-fat diet has its roots in the early 1900s. The presumed benefit of a low-fat diet was probably derived from the fact that fat is the most calorically dense macronutrient with nine calories per gram compared to four calories per gram for carbohydrate and protein. By limiting fat, people theorized they could eat more but limit weight gain.
In the 1940s, concern over heart disease deaths (the leading cause of death in the United States) prompted investigations such as the Framingham Study and Seven Countries Study. From these studies and others, researchers promoted the diet-heart hypothesis, which postulates saturated fats and cholesterol are the main causes of heart disease.
While the diet-heart hypothesis was far from proven, it seemed to be the best hypothesis on the origin of heart disease in the 1950s. Based on that hypothesis, in 1961 the American Heart Association (AHA) published a report advocating the prevention of heart disease by reducing dietary fat, but the authors were careful to note, “It must be emphasized that there is as yet no final proof that heart attacks or strokes will be prevented by such measures.”
Initially the AHA recommended a low-fat diet for individuals at high-risk for developing heart disease. Despite criticism from skeptics of the low-fat diet, in 1977 that the United States government advocated a low-fat diet for the general public in the report, Dietary Goals for the United States.
By 1980, a scientific consensus had emerged that the low-fat diet could help reduce risk of heart disease and cancer. The Surgeon General and the World Health Organization began promoting the low-fat diet, and soon food manufacturers saw opportunities to profit from the low-fat products. But in the place of fat, manufacturers added sugar to many products, creating low-fat but high-calorie foods.
In 1988, the AHA launched a program to label foods as “heart healthy.” Food manufacturers could pay for the AHA’s seal of approval if their product met the low-fat criteria. Soon foods such as Kellogg’s Frosted Flakes, Fruity Marshmallow Krispies, and low-fat Pop Tarts earned the “heart healthy” seal of approval. On the subject, Ann La Berge writes, “No wonder consumers were confused and assumed that low-fat was what really counted in terms of health. It was possible to think that if a food were low-fat, one could eat to appetite. We begin to see how a profusion of products low in fat but high in sugar and calories might ironically promote the fattening of America, even while being labeled heart-healthy.”
While the low-fat diet reigned supreme in the 1990s, more scientific dissenters came forward. Dr. Jules Hirsch, a leading obesity researcher at Rockefeller University, found that when the fat content of a diet was less than 20 percent, the body begins to synthesize saturated fat from carbohydrates. Dr. Walter Willett at the Harvard School of Public Health identified that substituting carbohydrates for fats reduced HDL cholesterol and increased triglycerides, both of which increase risk of developing heart disease.
Through the 1990s and into the 2000s, the growing popularity of high-fat diets, such as Atkins or the Mediterranean diets, led to the realization that eating fat does not necessarily make a person fat.
Further, scientists showed that not all fat had the same effect on the body. Trans fats increased, while omega-3 fats decreased heart diseased risk. While broad acceptance of the idea has been slow, even saturated fats have been shown to not increase the risk of heart disease.
Today, the low-fat diet is still popular but multiple studies have shown it to be no more effective, and sometimes less effective, than other diets at reducing heart disease or promoting weight loss (1, 2, 3). The United States government’s attempt to reduce heart disease using the low-fat diet has failed. Heart disease is still the leading cause of death and obesity has rapidly increased since its low-fat recommendations were implemented.
The low-fat diet is a regimen that can be effective, if overall calorie intake is also reduced. Many of the benefits of a low-fat diet may not directly come from the reduction of fat in the diet, but as a result of weight loss from caloric reduction. If a low-fat diet is used to maintain a healthy weight, then it will be beneficial. But, if a low-fat diet fails to reduce overall caloric intake, then it is unlikely that health benefits will be attained.
Over the past half-century dietary fat has been unfairly demonized and some low-fat foods have been irrationally promoted. With the exception of trans fat, dietary fat can be incorporated into a healthy diet, as evidenced by the cardiovascular and weight loss benefits of low-carbohydrate (i.e. Atkins) and Mediterranean diets. Low-fat diets can provide health benefits, if they incorporate healthy fats like omega-3 and result in maintenance of a healthy weight, but the current body of scientific knowledge indicates that a diet does not have to be low in fat to be healthy.