Eating less dietary saturated fat can reduce the risk of heart disease, but only when people consume more polyunsaturated fat and not more refined carbohydrates instead, conclude two groups of researchers from HSPH and their colleagues in two recent meta-analyses that leverage the statistical power of pooling the best observational studies or clinical trials of diet and heart disease events.
For the last half century, U.S. health experts have advised people to eat less saturated fat and more carbohydrates to prevent and to treat cardiovascular disease. Yet the evidence that this advice actually works has been surprisingly uncertain and sometimes contradictory.
The advice—often expanded to include less total dietary fat—seemed to have a broad scientific base, ranging from ecological studies of populations with better cardiovascular health profiles, such as in Japan, to studies of biological risk factors, such as blood cholesterol levels, as surrogate endpoints.
The two new systematic reviews show a more complicated story. One meta-analysis of 21 prospective epidemiologic studies totaling about 347,700 people found no significant association between saturated fat and increased risk of coronary heart disease or stroke.
“Simply reducing saturated fat in the diet will not confer cardiovascular benefits,” said coauthor Frank Hu, HSPH professor of nutrition and epidemiology. The analysis is published in the March American Journal of Clinical Nutrition.
But eating polyunsaturated fat in place of saturated fat will do some good, according to a meta-analysis of eight randomized controlled clinical trials totaling 13,600 people. The report of a modest but important benefit is published in the March 23 open-access journal PLoS Medicine.
More polyunsaturated fat will make a healthier diet, but ultimately “many other dietary changes will have as big or bigger benefits, such as eating much more fish, fruits and vegetables, and whole grains, and cutting back on processed foods and salt,” said first author Dariush Mozaffarian, assistant professor of epidemiology at HSPH and of medicine at HMS.
Going forward, “reducing refined carbohydrates and preventing obesity should be the highest priorities for coronary heart disease prevention,” Hu said.
For more information, students may contact Dariush Mozaffarian at dmozaffa@hsph.harvard.edu or Frank Hu at nhbfh@channing.harvard.edu.
Conflict Disclosure: The authors declare no conflicts of interest.
Funding Sources: AJCN study: National Institutes of Health, National Center for Research Resources, National Dairy Council, Unilever Corporate Research; PLoS study: National Heart, Lung, and Blood Institute; Searle Funds/Chicago Community Trust; the authors are solely responsible for the content of this work.
