1. In two large prospective cohort studies, dietary saturated and trans-fats were linked to increased rates of mortality. Poly- and mono-unsaturated fats were associated with decreased mortality.
2. Replacement of 5% of daily caloric intake from saturated fats with either poly- or mono-unsaturated fatty acids was associated with significant reduction in mortality.
Evidence Rating Level: 2 (Good)
Study Rundown: The role of dietary fatty acids in the prevention or promotion of cardiovascular disease and other health problems remains a topic of debate. Current guidelines recommend limiting consumption of saturated (SFAs) and trans-fatty acids (TFAs) while poly-unsaturated (PUFAs) and monounsaturated fatty acids (MUFAs) are promoted for their perceived health benefits. This study of two large prospective cohorts sought to estimate risk of mortality associated with the reported consumption of different fatty acids.
In a combined cohort of 126 233 previously healthy healthcare professionals over 26 years of follow-up, higher intake of SFA and TFA were both associated with increased risk of all-cause mortality. In contrast, PUFAs and MUFAs were both associated with lower risk of mortality. Consumption of linoleic acid (a PUFA) in particular was linked to reduced mortality. When 5% of energy from SFAs was substituted for the same quantity of energy from PUFA or MUFA, there was an associated reduction in mortality. The strength of this study was the long-term follow, which helped to capture meaningful endpoints. The major limitation of the study was reliance on self-reported dietary content, which can introduce significant bias. Also, the diet may have been a surrogate marker for a general ‘healthy’ lifestyle, which may have been the driving force behind the reduced mortality rather than the specific dietary fats.
Relevant Reading: 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
In-Depth [prospective cohort]: This study combined data from the Nurses’ Health Study (NHS, n = 83 349 women) and Health Professionals Follow-up Study (HPFS, n = 42 844 men) over 32 (NHS) and 26 (HPFS) years of follow-up. Individuals were included if they had no history of cardiovascular disease at baseline and had completed dietary surveys. Dietary data was obtained from the semi-quantitative food frequency questionnaire at regular intervals while information on general health status was obtained through biannual surveys.
In multifactorial analysis accounting for known cardiovascular risk factors, the risk of all-cause mortality was compared between highest and lowest quintile of fatty acid consumption. High SFA consumption had a hazard ratio of 1.08 (95%CI 1.03-1.14, p < 0.001) for mortality while TFA intake had a hazard ratio of 1.13 (95%CI 1.07-1.18, p < 0.001). PUFA and MUFA intake was associated with a lower mortality risk with HR 0.81 (95%CI 0.78-0.84, p < 0.001), and 0.89 (95%CI 0.84-0.94, p < 0.001), respectively. Linoleic acid specifically had mortality benefit with HR 0.82 (95%CI 0.79-0.86, p < 0.001). When 5% of energy from SFA was replaced with PUFA there was an associated reduction in mortality of 27% (HR 0.73, 95%CI 0.70-0.77), and substitution with MUFA had a 13% reduction in mortality (HR 0.87, 95%CI 0.82-0.93).
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