Nutrition advice has performed some spectacular flip-flops over the years. Eggs were banished from the breakfast table, then later welcomed back. Margarine was deemed healthier than butter—until researchers determined that the trans fats used to make the first generation of margarines were much harder on the heart than butter.
Yet one dietary guideline has stood fast for half a century: Saturated fat, found chiefly in meat and high-fat dairy products such as cheese, is bad—because it leads to clogged arteries, heart attacks and strokes. Now that certainty isn’t just wobbling; it’s toppling. According to recent research, saturated fat may not be a villain after all. In fact, some foods high in saturated fat may lower your risk of stroke and type 2 diabetes. And steering clear of foods just because they contain saturated fat, and eating other foods just because they are low in saturated fat, may be the unhealthiest choice of all.
One of the most prominent proponents of rewriting the book on saturated fat is cardiologist Dariush Mozaffarian, an associate professor of medicine at Harvard Medical School and the author of more than 100 scientific papers on nutrition and health. We asked him to explain why the conventional wisdom on saturated fat is misleading—and how eating it, in moderation, can sometimes be the healthiest move you could make.
Q: Saturated fat has been dietary public health enemy number one for decades. Why do you think telling people to avoid it is bad advice?
A: The recommendation to cut back on saturated fat was based on concerns that it raises the risk of heart disease. But we’ve learned that its effects are more complex than we first thought.
We’ve known since the 1960s that saturated fat raises LDL cholesterol, the “bad” cholesterol. But LDL is just one biomarker for risk. We now know that there are other cholesterol-containing particles, called HDL, that are related to a lower risk of heart disease. We also know that high levels of triglycerides in the blood, along with other factors, predict heart disease risk. Saturated fat does raise LDL cholesterol. But compared to carbohydrates, it also raises HDL cholesterol and lowers triglycerides. If we looked just at LDL, we would predict that saturated fat raises heart disease risk. If we looked at the effect of saturated fat on HDL and triglycerides, we would suppose that saturated fat lowers that risk. If we looked at the combination, we would predict that saturated fat is relatively neutral for heart disease risk compared to carbohydrates.
Q: So is saturated fat good or bad?
A: To answer that, we need to study how eating saturated fat relates to actual diseases, not simply to biomarkers such as blood cholesterol that only suggest the possibility of artery damage. Three groups of researchers have recently weighed data from all available large long-term studies that have tracked saturated-fat intake and heart attacks or strokes. All three found no association between saturated fat and heart attacks or strokes. People who consumed the highest levels of saturated fat had about the same rates of heart disease as people who consumed the least.
Q: Those are amazing results, given decades of advice to cut back on saturated fat. How do you explain them?
A: When you ask whether saturated fat is good or bad, the question should be, “Compared to what?” Compared to polyunsaturated fat from vegetable oils, saturated fat is clearly more harmful to the heart. But compared to trans fat, saturated fat is healthier. Compared to carbohydrates, a category that includes starches and grains as well as sugary foods, saturated fat is probably neutral. But compared to refined carbohydrates—the kind found in white breads, most breakfast cereals and snack foods and sweets, for -instance—many foods with saturated fat appear to be a better choice. They also seem less likely than refined carbohydrates to raise heart disease risk.