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Cutting Back on Saturated Fats? The Benefit Depends on the Replacement

Carbohydrate substitutes do not decrease heart disease risk.

Saturated fats – found in fried foods, fatty meats, and butter – have long been viewed as a culprit of heart disease. Dietary intake of saturated fats results in increased LDL cholesterol and thus an increase in risk of heart disease. Few studies have focused on comparing carbohydrates to saturated fats in terms of heart disease risk.

To address this gap in data, researchers from the Harvard T.H. Chan School of Public Health examined data from 4,268 healthy women and 42,908 healthy men who did not have cardiometabolic diseases or cancer at baseline. The subjects’ diets were assessed via a questionnaire every four years. The follow-up period was 24 to 30 years, with almost 7,500 instances of coronary heart disease.

After assessing the subjects’ diets, the researchers found that increased intake of polyunsaturated fatty acids and carbohydrates from whole grain sources resulted in a lower incidence of coronary heart disease than higher intake refined carbohydrates. Furthermore, they found that there was no difference in heart disease risk when refined carbohydrates were replaced with saturated fats (p > 0.10).

Replacing 5% of energy from saturated fats with polyunsaturated fatty acids, monounsaturated fatty acids, or carbohydrates from whole grain sources resulted in lower risk of heart disease: 25% reduced risk, 15% reduced risk, and 9% reduced risk respectively (Polyunsaturated fatty acids: HR 0.75, 95% CI 0.67 to 0.84, p < 0.0001; monounsaturated fatty acids: HR 0.85, 95% CI 0.74 to 0.97, p = 0.02; carbohydrates from whole grains: HR 0.91; CI 0.85 to 0.98; p = 0.01).

The results of the study show that the benefit of cutting back on saturated fats depends on what the saturated fats are replaced with. Clinicians can recommend that patients replace saturated fats and refined carbohydrates with unsaturated fats and carbohydrates from whole grain sources to reduce their risk of coronary heart disease. Polyunsaturated fatty acids appear to have the biggest benefit. These changes can be very simple, such as cooking with olive oil instead of butter. However, replacing saturated fats with refined carbohydrates such as pasta, white bread, and sugar, does not show any improvement in risk of heart disease.

One flaw in the study is reliance on self-reporting, especially at such extended intervals as every four years. Subjects may not have reported their diets correctly. More research, ideally a clinical randomized controlled trial, is necessary to confirm the results of this prospective cohort study.

Practice Pearls:

  • Saturated fats are associated with an increased risk of heart disease via increased LDL levels.
  • Replacing saturated fats with refined carbohydrates results in no change in heart disease risk.
  • Replacing saturated fats with polyunsaturated fatty acids, monounsaturated fatty acids, or carbohydrates from whole grain sources does result in decreased heart disease risk.

Li Y, Hruby A, Bernstein A et al. Saturated Fats Compared With Unsaturated Fats and Sources of Carbohydrates in Relation to Risk of Coronary Heart Disease. Journal of the American College of Cardiology. 2015;66(14):1538-1548.doi:10.1016/j.jacc.2015.07.055.