We have been told that saturated fat is unhealthy for so long by so many that most of us now just consider it common sense and would never think to question it. The presumption that dietary saturated fat causes heart disease (known as the “Diet-Heart Hypothesis”) is one of the fundamental tenements of major institutions like the American Heart Association, the National Heart, Lung, and Blood Institute, and The United States Department of Agriculture, so most would assume that their guidelines are based on sound scientific fact. But those who take the time to honestly evaluate the evidence will quickly see that no study has yet to show a solid causal link between consumption of saturated fat and the development of heart disease, cancer, diabetes, etc.
When it comes to the Diet-Heart Hypothesis, the phrase “passions verging on zealotry” belongs to one man above all others: Ancel Keys. His 1952 chart, “Fat Calories vs Deaths from Degenerative Heart Disease”, appears to show a nice and tidy upward curve connecting increased consumption of fat (shown along the X axis) and increased deaths per 1,000 from heart disease (going up the Y axis). But as many critical observers have pointed out, there are two big problems with this graph, and the theory it attempts to prove.
- The same curve could be plotted to show a correlation between deaths per 1,000 and per capita car ownership, cigarette sales, protein consumption, and sugar consumption—essentially everything that came along with increases in wealth in the mid-20th century. Any one of these factors (or some combination of them) could be the cause of the increased rates of heart disease we’ve seen over the past 100 years. But we can’t be sure because Keys’ study can only tease out correlative relationships.
- Keys created the graph by cherry-picking countries with data that fit his hypothesis. If one were to include a larger number of data points, as Jacob Yerushalmy (the founder of the Biostatistics Department at the University of California, Berkeley) did in 1957 with 22 countries, a clean upward line can no longer be drawn and the correlation between dietary fat and heart disease evaporates. But even if a correlation had remained after adding in more countries, we have to remember that at best, epidemiological (i.e. observational) studies like these can only show a possible correlation between saturated fat and disease. By definition, such studies cannot prove causation. As every scientist knows (or rather, should know since many often seem to forget), correlation is not causation.
Okay, so observational studies cannot prove that dietary saturated fat causes heart disease. But what about controlled scientific trials? Bad news there, too, for the fat-phobic:
- The Women’s Health Initiative (WHI): 49,000 women were put on a low-fat diet in what would be the largest, longest trial ever conducted on the connection between fat consumption and disease. The results? Women did not lose weight as expected and saw no significant change in their risk for heart disease or cancer.
- The Framingham Heart Study: Though this study is often cited in support of the Diet-Heart Hypothesis, the study’s director actually made the conclusion (perhaps unintentionally) that eating fat made one more fit and active: “In Framingham, the more saturated fat one ate, the more cholesterol one ate, the more calories one ate, the lower the person’s serum cholesterol…We found that the people who the most cholesterol, ate the most saturated fat, ate the most calories, weighed the least, and were the most physically active.”
- The American MRFIT Study: Like the Framingham Heart Study, the MRFIT Study is also used frequently to support the Diet-Heart Hypothesis even though it showed some startling—albeit seldom reported—results. The study showed, for example, those who ate less animal fat and Cholesterol actually had higher blood cholesterol!
Nina Teicholz’s The Big Fat Surprise sums up the Diet-Heart Hypothesis’ failure quite nicely:
“If, in recommending that Americans avoid meat, cheese, milk, cream, butter, eggs, and the rest, it turns out that nutrition experts made a mistake, it will have been a monumental one. Measured just by death and disease, and not including the millions of lives derailed by excess weight and obesity, it’s very possible that the course of nutrition advice over the past sixty years has taken an unparalleled toll on human history. It now appears that since 1961, the entire American population has, indeed, been subjected to a mass experiment, and the results have clearly been a failure. Every reliable indicator of good health is worsened by a low-fat diet. Whereas diets high in fat have been shown, again and again, in a large body of clinical trials, to lead to improved measures for heart disease, blood pressure, and diabetes, and are better for weight loss. Moreover, it’s clear that the original case against saturated fats was based on faulty evidence and has, over the last decade, fallen apart. Despite more than two billion dollars in public money spent trying to prove that lowering saturated fat will prevent heart attacks, the diet-heart hypothesis has not held up.”
Michael Chase, MS, NTP
Nutrition Science and Dietetics
