Abstract
To examine the associations of specific dietary fats with total and cause-specific mortality in two large ongoing prospective cohort studies.
Generated Summary
This study, published in JAMA Internal Medicine, investigated the relationship between specific dietary fats and total and cause-specific mortality. The research employed a prospective cohort study design, analyzing data from the Nurses’ Health Study (NHS) and the Health Professionals Follow-up Study (HPFS). These studies involved 83,349 women and 42,884 men, respectively, who were free from cardiovascular disease, cancer, and diabetes at baseline. The primary aim was to examine how various dietary fats, including saturated, polyunsaturated, monounsaturated, and trans fats, were associated with mortality outcomes. The researchers collected dietary information through semi-quantitative food frequency questionnaires (SFFQs) and assessed mortality by linking participants’ records with state vital records and the National Death Index. The study’s methodology included Cox proportional hazard models to estimate hazard ratios (HRs) and 95% confidence intervals (CIs), along with sensitivity analyses and isocaloric substitution models to assess the impact of replacing one type of fat with another. The investigation spanned several decades, allowing for a comprehensive analysis of long-term dietary habits and their health consequences.
Key Findings & Statistics
- The study documented 33,304 deaths during 3,439,954 person-years of follow-up in the NHS and HPFS cohorts.
- Dietary total fat, compared to total carbohydrate, was inversely associated with total mortality (P for trend <0.001).
- The hazard ratios (HRs) of total mortality comparing extreme quintiles of specific dietary fats were: 1.08 (95% CI, 1.03-1.14) for saturated fat, 0.81 (95% CI, 0.78-0.84) for polyunsaturated fat, 0.89 (95% CI, 0.84-0.94) for monounsaturated fat, and 1.13 (95% CI, 1.07-1.18) for trans fat (P for trend <0.001 for all).
- Replacing 5% of energy from saturated fats with equivalent energy from polyunsaturated fats and monounsaturated fats was associated with 27% (HR = 0.73, 95% CI, 0.70-0.77) and 13% (HR = 0.87, 95% CI, 0.82-0.93) estimated reductions in total mortality, respectively.
- HR of total mortality comparing extreme quintiles of n-6 polyunsaturated fat intake was 0.85 (95% CI, 0.81-0.89).
- The HR for linoleic acid intake was 0.82 (95% CI, 0.79-0.86, P for trend <0.001).
- Intake of total n-3 PUFA was associated with modestly lower total mortality, which was mainly driven by the inverse association of marine n-3 PUFAs with total mortality.
- HRs comparing extreme quintiles were 0.95 (95% CI, 0.91-0.99, P for trend = 0.03) for total n-3 PUFAs and 0.96 (95% CI, 0.93-1.00, P for trend = 0.002) for marine n-3 PUFAs.
- SFA intake, when substituted for total carbohydrates, was not significantly associated with CVD mortality (P for trend across quintiles = 0.17), while TFA intake was associated a 20% higher CVD mortality across quintiles (HR = 1.20, 95% CI, 1.08-1.33, P for trend <0.001).
- PUFA intake was inversely associated with CVD mortality (P for trend <0.001).
- We observed an inverse association, primarily in women, between MUFA intake and CVD mortality (P for trend =0.01).
- Among specific PUFAs, linoleic acid intake was most strongly related to lower risk of CVD mortality (P for trend <0.001).
- Dietary intake of SFA, when substituted for total carbohydrate, was associated with slightly higher cancer mortality (HR comparing extreme quintiles =1.07, 95% CI, 0.98-1.17, P for trend =0.02).
- Replacing 5% of energy from SFAs with the same energy from PUFAs and MUFAs was associated with 27% (HR =0.73, 95% CI, 0.70-0.77) and 13% (HR =0.87, 95% CI, 0.82-0.93) estimated reduction in total mortality, respectively.
- Replacing SFAs with the same energy from PUFAs was associated with lower risk of mortality due to CVD, cancer and neurodegenerative disease.
- Replacement of 5% of energy from SFAs with 5% of energy from MUFAs was associated with 29% estimated reduction in neurodegenerative disease mortality (HR =0.71, 95% CI, 0.57-0.88).
Other Important Findings
- The study found that different types of dietary fats have divergent associations with total and cause-specific mortality.
- Higher intakes of PUFA and MUFA were associated with lower mortality, whereas higher intakes of SFA and TFA were associated with increased mortality.
- The association between total fat intake and mortality largely depends on specific types of fat.
- Intake of linoleic acid showed strong inverse associations with total and most cause-specific mortality, without any evidence of detrimental effects.
- A higher ratio of n-6 to n-3 PUFAs was not associated with increased mortality, but with a slightly lower total, CVD, and cancer mortality.
- Marine n-3 PUFA intake was inversely associated with respiratory disease mortality.
- The inverse associations became stronger in continuous analyses and when recent intakes of total and marine n-3 PUFAs were used.
Limitations Noted in the Document
- Reverse causation could be a possible explanation for the findings, as individuals with chronic diseases might change their diet.
- The observational nature of the study means causality cannot be established.
- Residual confounding could not be ruled out despite adjusting for potential confounders.
- Measurement errors in food and nutrient intakes are inevitable, though the study used cumulatively averaged intake to reduce their impact.
Conclusion
The findings from this study underscore the importance of specific types of dietary fat in relation to overall health and longevity. The research suggests that replacing saturated fats with unsaturated fats can significantly lower the risk of both total and cause-specific mortality. The study highlights that not all fats are created equal; while higher intakes of saturated and trans fats were associated with increased mortality risks, higher intakes of polyunsaturated and monounsaturated fats were linked to lower mortality rates. These results reinforce the importance of dietary recommendations that advocate for the elimination of partially hydrogenated oils, which are a primary source of trans fatty acids, and the incorporation of unsaturated fats in place of saturated fats. Furthermore, the study supports the need for future research to confirm the novel associations identified, particularly those concerning the relationships between specific types of fat and mortality from neurodegenerative and respiratory diseases. The strong inverse associations observed with linoleic acid and marine n-3 PUFAs suggest the importance of considering the quality of carbohydrates as well, as the effects of replacement by carbohydrates may depend, in part, on the type of carbohydrates consumed.