People who replace saturated fat (mainly found in meats and dairy foods) in their diets with refined carbohydrates do not lower their risk of heart disease, according to a new study led by researchers at Harvard T.H. Chan School of Public Health. On the other hand, those who replace saturated fats with unsaturated fats (found in vegetable oils and nuts) or whole grains lower their heart disease risk.

Many people fall back on carbs, especially refined carbs like white bread, when they reduce saturated fat in their diets, said senior author Frank Hu, professor of nutrition and epidemiology. This may in part explain findings from a controversial 2014 paper that called into question recommendations for limiting saturated fat for heart health, and led to headlines promoting the return of butter.

“Our research does not exonerate saturated fat,” said Hu. “In terms of heart disease risk, saturated fat and refined carbohydrates appear to be similarly unhealthful.”

The study appears online Sept. 28 in the Journal of the American College of Cardiology.

A strong start toward good health: Good choices

This is the first prospective analysis to directly compare saturated fat with other types of fats and different types of carbohydrates in relation to heart disease risk.

Hu and colleagues looked at diet and health information from participants in two long-running trials, the Nurses’ Health Study (84,628 women) and the Health Professionals Follow-up Study (42,908 men), who were free of diabetes, cardiovascular disease, and cancer at baseline. Diet was assessed by food frequency questionnaires every four years. During follow-up, the researchers documented 7,667 cases of coronary heart disease (CHD).

They estimated that replacing 5 percent of energy intake from saturated fats with equivalent energy intake from either polyunsaturated fats, monounsaturated fats, or carbohydrates from whole grains was associated with 25 percent, 15 percent, and 9 percent lower risk of CHD, respectively. On the other hand, swapping 5 percent of saturated fat calories for the same amount of refined carbohydrates and sugars was not associated with CHD risk. These analyses took into account cardiovascular risk factors such as age, body mass index, smoking, and physical activity.

“Our findings suggest that the low-fat, high-carb trends of the 1980s and 1990s are not effective in reducing risk of CHD,” said Yanping Li, co-first author with Adela Hruby, both researchers in the Department of Nutrition. “It means that individuals should not replace saturated fat with refined carbs or vice versa. Dietary recommendations to reduce saturated fats should specify their replacement with unsaturated fats or with healthy carbohydrates, such as whole grains,” said Li.

Other Harvard Chan School authors of the study included Sylvia Ley, Dong Wang, Stephanie Chiuve, Laura Sampson, Eric Rimm, and Walter Willett.