HAMILTON, Ontario — Saturated fats were not associated with all-cause mortality, cardiovascular disease, coronary heart disease, ischemic stroke or type 2 diabetes in a systematic review funded by the World Health Organization (WHO). Any health effects associated with replacing saturated fats in products may depend on what ingredients replace them, according to the review, which appeared online Aug. 12 in the BMJ.
Trans fats, on the other hand, were associated with all-cause mortality, coronary heart disease and coronary heart disease mortality in the review, “Dietary guidelines must carefully consider the health effects of recommendations for alternative macronutrients to replace trans fat and saturated fats,” the authors of the review said.
Few observational studies have modeled the effect of replacing saturated fat or trans fat with other nutrients, they said.
“In large prospective studies, when polyunsaturated fats replace saturated fats, risk of CHD (coronary heart disease) is reduced but not when MUFA (monounsaturated fatty acids) or carbohydrate is the replacement choice,” they said.
Dietary advice tends to recommend limiting intake of both saturated fat and trans fat. The American Heart Association recommends that healthy Americans over age 2 limit their saturated fat intake to less than 7 percent of total daily calories and their trans fat intake to less than 1 percent. The 2015 Dietary Guidelines Advisory Committee recommended people limit daily saturated fat intake to less than 10 percent of total calories. The WHO said lowering saturated fat intake to less than 10 percent of total energy intake and trans fats to less than 1 percent reduces the risk of developing non-communicable diseases.
The study appearing in the BMJ involved researchers from McMaster Univ. and Hamilton Health Sciences in Hamilton, Ont., as well as from the Univ. of Toronto and the Hospital for Sick Children in Toronto. They examined 41 primary reports of associations between saturated fats and health outcomes in prospective cohort studies published between 1981 and 2014.
Risks were associated with what ingredients replaced saturated fat. A pooled analysis of 11 prospective cohort studies found replacement of saturated fat with polyunsaturated fat reduced coronary risk by 13 percent.
Researchers said foods high in saturated fat, particularly processed and red meat, have been associated with increased mortality and risk of cancer, but dairy foods were not consistently associated with cancers.
“The association between certain foods and CHD cannot be predicted solely by their content of total saturated fats because individual saturated fats might have different cardiovascular effects, and major food sources of saturated fats contain other constituents that could influence risk of CHD,” the researchers said.
Studying a Southern-style diet
The review appeared in the BMJ two days after a study showing an increased risk of heart disease among people who eat a Southern-style diet appeared online Aug. 10 in Circulation, an American Heart Association (AHA) journal. The study characterized a Southern-style diet as one that involves people eating a lot of fried foods, fatty foods, eggs, processed meat and organ meats.
The study of more than 17,000 white and African American adults found people who most often ate foods conforming to the Southern dietary pattern had a 56 percent higher risk of heart disease compared to those who ate it less frequently. The National Institute of Neurological Disorders and Stroke; the National Heart, Lung, and Blood Institute; and the General Mills Bell Institute of Health and Nutrition funded the study, which involved researchers from the University of Alabama at Birmingham.
Results from the study in the BMJ more closely were aligned with the AHA’s trans fat guidance. The researchers examined 20 primary reports of associations between total trans fats and the health outcomes in prospective cohort studies published between 1996 and 2015. They found a 2 percent increase in energy from trans fats is associated with a 25 percent increased risk of coronary heart disease and a 31 percent increase in coronary heart disease mortality.
The review in the BMJ may be found here.