Saturated and Trans Fats and Mortality, CVD, and Diabetes
- de Souza RJ, Mente A, Maroleanu A, 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;Aug 11:[Epub ahead of print].
The following are key points to remember from a review on intake of saturated and trans unsaturated fatty acids and risk of all-cause mortality, cardiovascular disease (CVD), and type 2 diabetes:
- Dietary guidelines have recommended that saturated fats should be limited to <10% (5-6% for those who would benefit from lowering of low-density lipoprotein cholesterol), and trans fats to <1% of energy or as low as possible, primarily to reduce risk of ischemic heart disease and stroke. There has been a long-standing controversy regarding these guidelines, which had the potential to include bias of many types including clinical, scientific, publication, and commercial.
- Prospective cohort studies have shown no relationship between coronary heart disease (CHD), stroke, or CVD and extremes of intake of saturated fats (usually 10% of energy), of which the main sources of saturated fatty acids include butter, cow’s milk, meat, salmon, egg yolks, chocolate, coconut, and palm kernel oils. In contrast, a meta-analysis of randomized trials suggested a 17% reduction in risk of CVD in studies that reduced saturated fat intake from about 17% to about 9% of energy.
- Trans fats contribute about 1-2% of energy in the North American diet and are produced industrially through partial hydrogenation of liquid vegetable fats for use in margarine, snack food, packaged baked goods, and frying fast food. A meta-analysis reported pooled relative risk estimates for CHD of 1.22 (p = 0.002) for extremes of total intake of trans fats, the majority of which is industrially produced.
- This very well done systematic review and meta-analysis reviewed prospective observational studies, of which 73 publications were eligible. In the final analysis, 41 prospective cohorts could be used in a GRADE quantitative evidence of synthesis. As with other recent similar analysis, there was no association between saturated fats and health outcomes in studies where saturated fat generally replaced refined carbohydrates, but there was a positive association between total trans fatty acids and health outcomes.
- There appears to be good justification for the recent liberalization of fat intake of various types. The dietary guidelines for saturated and trans fatty acids must carefully consider the effect of replacement nutrients. Intervention studies support a CHD and CVD risk reduction benefit with the substitution of both monounsaturated fatty acids and polyunsaturated fatty acids for saturated fat (particularly for trans fats), as well as replacing them with high-quality carbohydrates from whole fruits, vegetables, and grains with a lower glycemic index.
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