Abstract
Previous studies have shown distinct associations between specific dietary fat and cardiovascular disease. However, evidence on specific dietary fat and mortality remains limited and inconsistent. To examine the associations of specific dietary fats with total and cause-specific mortality in 2 large ongoing cohort studies. This cohort study investigated 83 349 women from the Nurses’ Health Study (July 1, 1980, to June 30, 2012) and 42 884 men from the Health Professionals Follow-up Study (February 1, 1986, to January 31, 2012) who were free of cardiovascular disease, cancer, and types 1 and 2 diabetes at baseline. Dietary fat intake was assessed at baseline and updated every 2 to 4 years. Information on mortality was obtained from systematic searches of the vital records of states and the National Death Index, supplemented by reports from family members or postal authorities. Data were analyzed from September 18, 2014, to March 27, 2016. Total and cause-specific mortality. During 3 439 954 person-years of follow-up, 33 304 deaths were documented. After adjustment for known and suspected risk factors, dietary total fat compared with total carbohydrates was inversely associated with total mortality (hazard ratio [HR] comparing extreme quintiles, 0.84; 95% CI, 0.81-0.88; P < .001 for trend). The 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 fatty acid (PUFA), 0.89 (95% CI, 0.84-0.94) for monounsaturated fatty acid (MUFA), and 1.13 (95% CI, 1.07-1.18) for trans-fat (P < .001 for trend for all). Replacing 5% of energy from saturated fats with equivalent energy from PUFA and MUFA was associated with estimated reductions in total mortality of 27% (HR, 0.73; 95% CI, 0.70-0.77) and 13% (HR, 0.87; 95% CI, 0.82-0.93), respectively. The HR for total mortality comparing extreme quintiles of ω-6 PUFA intake was 0.85 (95% CI, 0.81-0.89; P < .001 for trend). Intake of ω-6 PUFA, especially linoleic acid, was inversely associated with mortality owing to most major causes, whereas marine ω-3 PUFA intake was associated with a modestly lower total mortality (HR comparing extreme quintiles, 0.96; 95% CI, 0.93-1.00; P = .002 for trend). Different types of dietary fats have divergent associations with total and cause-specific mortality. These findings support current dietary recommendations to replace saturated fat and trans-fat with unsaturated fats.
Generated Summary
This study investigated the associations between specific dietary fats and total and cause-specific mortality using data from two large, ongoing cohort studies: the Nurses’ Health Study (NHS) and the Health Professionals Follow-up Study (HPFS). The NHS followed 83,349 women from July 1, 1980, to June 30, 2012, and the HPFS followed 42,884 men from February 1, 1986, to January 31, 2012. Participants were free of cardiovascular disease, cancer, and diabetes at baseline. Dietary fat intake was assessed through questionnaires at baseline and updated every 2 to 4 years. Information on mortality was obtained from vital records and the National Death Index, supplemented by reports from family members. Data analysis was performed from September 18, 2014, to March 27, 2016, to examine the associations of specific dietary fats with total and cause-specific mortality. Cox proportional hazards regression models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) of mortality, with isocaloric substitution models used to assess the impact of replacing one type of fat with another. Sensitivity analyses were conducted to assess the robustness of the findings. The study aimed to examine the associations of specific dietary fats with total and cause-specific mortality to inform current dietary recommendations.
Key Findings & Statistics
- During 3,439,954 person-years of follow-up, 33,304 deaths were documented.
- Total fat compared with total carbohydrates was inversely associated with total mortality (HR comparing extreme quintiles, 0.84; 95% CI, 0.81-0.88; P < .001 for trend).
- Saturated fat: HR 1.08 (95% CI, 1.03-1.14).
- Polyunsaturated fatty acid (PUFA): HR 0.81 (95% CI, 0.78-0.84).
- Monounsaturated fatty acid (MUFA): HR 0.89 (95% CI, 0.84-0.94).
- Trans-fat: HR 1.13 (95% CI, 1.07-1.18) (P < .001 for trend for all).
- Replacing 5% of energy from saturated fats with PUFA and MUFA was associated with estimated reductions in total mortality of 27% (HR, 0.73; 95% CI, 0.70-0.77) and 13% (HR, 0.87; 95% CI, 0.82-0.93), respectively.
- ω-6 PUFA intake: HR 0.85 (95% CI, 0.81-0.89; P < .001 for trend).
- Linoleic acid was inversely associated with mortality owing to most major causes.
- Marine ω-3 PUFA intake was associated with a modestly lower total mortality (HR comparing extreme quintiles, 0.96; 95% CI, 0.93-1.00; P = .002 for trend).
- For every 5% energy substituted from carbohydrates: total fat 0.95 (0.94-0.96), saturated fat 1.08 (1.04-1.11), unsaturated fat 0.85 (0.83-0.87), polyunsaturated fat 0.73 (0.69-0.77), monounsaturated fat 0.90 (0.87-0.94), and trans-fat 1.16 (1.09-1.24)
- For CVD mortality: saturated fat (P = .17), trans fat 1.20 (1.08-1.33).
- Cancer mortality: linoleic acid (P < .001), for total PUFA, the HR was 0.93 (0.87-0.99).
Other Important Findings
- Higher intakes of PUFA and MUFA were associated with lower mortality, whereas higher intakes of SFA and TFA were associated with increased mortality.
- The inverse association between total PUFA and mortality was mainly driven by linoleic acid.
- The inverse association between marine ω-3 PUFA intake and total mortality.
- Replacing SFAs with the same energy from PUFAs was associated with a lower risk for mortality due to CVD, cancer, and neurodegenerative disease.
- Replacing 5% of energy from SFAs with 5% of energy from MUFAs was associated with a 29% estimated reduction in neurodegenerative disease mortality (HR, 0.71; 95% CI, 0.57-0.88).
- Higher w-6:w-3 PUFA ratio was not associated with increased mortality, but with a slightly lower CVD and cancer mortality.
- For cause specific mortality, there was an inverse association, primarily in women, between MUFA intake and CVD mortality.
Limitations Noted in the Document
- Reverse causation is a possible explanation for findings, as people with chronic diseases may alter their diet.
- The study was observational.
- Measurement errors are inevitable in estimates of food and nutrient intakes.
- Residual confounding could not be ruled out.
Conclusion
The findings support current dietary recommendations to replace saturated and trans-fat with unsaturated fats. The study demonstrated divergent associations of different types of dietary fats with total and cause-specific mortality. The study’s results emphasize that the association between total fat intake and mortality depends on the specific types of fat consumed. Replacing saturated fats with unsaturated fats was associated with reduced total mortality, and with lower risks for cardiovascular disease, cancer, and neurodegenerative diseases. The study also underscored the importance of linoleic acid, a w-6 PUFA, as it showed strong inverse associations with overall and cause-specific mortality. This evidence supports the need for current dietary guidelines that recommend replacing saturated and trans fats with unsaturated fats. The findings also suggest benefits from the consumption of marine ω-3 PUFAs, as well as the need for further research on the specific effects of various fatty acids on health outcomes. These dietary patterns are expected to be crucial in promoting health, especially considering the associations between dietary fats and major causes of mortality. Overall, the study provides a comprehensive look into the effects of specific dietary fats on health, offering a foundation for dietary guidance focused on improving population health outcomes and reducing the burden of chronic diseases. The study suggests that dietary recommendations should continue to emphasize the importance of replacing saturated and trans fats with unsaturated fats to promote better health outcomes.
IFFS Team Summary
- Study of 83K Women and 43K Men, from 1986 to 2012, 3.4 M person years and 33K deaths
- HR for mortality in quintiles of
- saturated fat (SFA) intake was 1.08
- trans fat intake (TFA) was 1.13
- polyunsaturated fats (PUFA) was 0.81
- monounsaturated fats (MUFA) was 0.89
- saturated fat (SFA) intake was 1.08
- trans fat intake (TFA) was 1.13
- polyunsaturated fats (PUFA) was 0.81
- monounsaturated fats (MUFA) was 0.89
- Replacing 5% of energy from SFA with PUFA and MUFA was associated with about 27% decreased mortality
- HR for total mortality comparing extreme quintiles of omega-6 PUFA intake was 0.85
- linoleic acid especially decreased mortality from most causes
- linoleic acid especially decreased mortality from most causes
- Total and Marine omega 3 fatty acids were associated with a slight benefit
- SFA associated with modest increase in cancer, MUFA PUFA modestly decreased cancer
- SFA and TFA increased neurodegenerative disease mortality (? dementia), while MUFA and PUFA decreased