Saturated Fats Not Linked to Greater Risk of Heart Disease
Trans fats are associated with greater risk of death and coronary heart disease, but evidence supporting a link between saturated fats and increased risk of death, heart disease, stroke, or type 2 diabetes is not as clear, according to a recent study.
“Simply telling people to eat less trans or saturated fat isn’t likely to be helpful,” says lead study author Russell de Souza, ScD, a registered dietician and assistant professor in the Department of Clinical Epidemiology and Biostatistics with the Michael G. DeGroote School of Medicine at McMaster University in Hamilton, Ontario, Canada. “We need to tell them what to replace it with, and a large body of evidence suggests that the best choices are foods that are high in plant fats, like olive oils and nuts, whole grains, and legumes.”
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Saturated fats mainly come from animal products, such as butter, cows’ milk, meat, salmon, and egg yolks, and some plant products such as chocolate and palm oils. Trans unsaturated fats (trans fats) are mainly produced industrially from plant oils for use in margarine, snack foods, and packaged baked goods.
Current guidelines recommend limiting saturated fat intake to less than 10% and trans fats to less than 1% to reduce risk of heart disease and stroke.
“Our review of the evidence supports that the removal of artificial trans fats from the food supply is the right idea—they offer no health benefit, and a serious risk of harm,” de Souza says.
“Though we failed to find a significant association between saturated fats and heart disease in observational studies, our certainty in this finding is very low because of the limitations of the study designs included,” he says. “We could not confidently rule out an increased risk of death from heart disease with higher amounts of saturated fat.”
de Souza and colleagues analyzed the results of 50 observational studies examining the association between saturated and/or trans fats and health outcomes in adults.
They did not find a clear association between higher intake of saturated fats and death for any reason, coronary heart disease (CHD), cardiovascular disease (CVD), ischemic stroke, or type 2 diabetes.
On the contrary, they found consumption of industrial trans fats was associated with a 34% increase in death for any reason, a 28% increased risk of CHD mortality, and a 21% increase in the risk of CHD.
Because of inconsistencies in the studies the team analyzed, the researchers could not confirm an association between trans fats and type 2 diabetes—and they found no clear association between trans fats and ischemic stroke.
While no definitive conclusions can be drawn about cause and effect because the results are based on observational studies, the authors write that their analysis confirms the findings of five previous systematic reviews of saturated and trans fats and CHD.
“There is no one nutrient or food that’s responsible for all heart disease, diabetes, or death. The whole diet matters,” de Souza says. “Dietary patterns consistently associated with good health, such as Mediterranean diets, plant-based diets, or the DASH diet, tend to be low in saturated fat, but their healthfulness is not due solely to the fact that they are low in saturated fat—it’s likely because they combine a number of foods that are highly nutritious.”
The authors’ review of the observational evidence does not support calls to increase the allowable amount of saturated fat in the diet at this time, given the limitations of the data due to study design.
“At the time we conducted this review, we had few studies to help us distinguish between the effects of artificial and natural trans fats,” de Souza says. “Now that exposure to artificial trans fats is much reduced, future studies will be better able to capture the effect of ‘natural’ trans fats on health, which will be very interesting.”
Investigators are now moving into the area of “dietary pattern” research—research that expands the focus from looking at the risks associated with individual nutrients, such as saturated fat, toward studies that look at the whole diet.
“People don’t eat individual nutrients, so we’d like to further explore the effects of combinations of foods on disease risk, which is more relevant to how people eat,” de Souza says.
de Souza RJ, Mente A, Maroleanu A, Cozma AI, Ha V, Kishibe T, et al. Intake of saturated and trans unsaturated fatty acids and risk of all cause mortality, cardiovascular disease, and type 2 diabetes: systematic review and meta-analysis of observational studies. BMJ. 2015;351:h3978.