Major types of dietary fat and risk of coronary heart disease: a pooled analysis of 11 cohort studies

Abstract

Background: Saturated fatty acid (SFA) intake increases plasma LDL-cholesterol concentrations; therefore, intake should be reduced to prevent coronary heart disease (CHD). Lower habitual intakes of SFAs, however, require substitution of other macronutrients to maintain energy balance.

Objective: We investigated associations between energy intake from monounsaturated fatty acids (MUFAs), polyunsaturated fatty acids (PUFAs), and carbohydrates and risk of CHD while assessing the potential effect-modifying role of sex and age. Using substitution models, our aim was to clarify whether energy from unsaturated fatty acids or carbohydrates should replace energy from SFAs to prevent CHD.

Design: This was a follow-up study in which data from 11 American and European cohort studies were pooled. The outcome measure was incident CHD.

Results: During 4-10 y of follow-up, 5249 coronary events and 2155 coronary deaths occurred among 344,696 persons. For a 5% lower energy intake from SFAs and a concomitant higher energy intake from PUFAs, there was a significant inverse association between PUFAs and risk of coronary events (hazard ratio: 0.87; 95% CI: 0.77, 0.97); the hazard ratio for coronary deaths was 0.74 (95% CI: 0.61, 0.89). For a 5% lower energy intake from SFAs and a concomitant higher energy intake from carbohydrates, there was a modest significant direct association between carbohydrates and coronary events (hazard ratio: 1.07; 95% CI: 1.01, 1.14); the hazard ratio for coronary deaths was 0.96 (95% CI: 0.82, 1.13). MUFA intake was not associated with CHD. No effect modification by sex or age was found.

Conclusion: The associations suggest that replacing SFAs with PUFAs rather than MUFAs or carbohydrates prevents CHD over a wide range of intakes.

FIGURE 1

Study-specific and combined hazard ratios and 95% CIs for coronary events (A) (n = 306,244) and coronary deaths (B) (n = 327,660) in the Pooling Project of Cohort Studies on Diet and Coronary Disease. The model included intake of monounsaturated fatty acids, polyunsaturated fatty acids (PUFAs), trans fatty acids, carbohydrates (CHs), and protein expressed as percentages of total energy intake (E%; as continuous variables), total energy intake (kcal/d; as a continuous variable), smoking (never smokers, former smokers, or current smoker of 1–4, 5–14, 15–24, or ≥25 cigarettes/d), BMI (in kg/m²; <23, 23 to <25, 25 to <27.5, 27.5 to <30, or ≥30), physical activity (levels 1–5), highest attained educational level (<high school, high school, or >high school), alcohol intake (0, 0 to <5, 5 to <10, 10 to <15, 15 to <30, 30 to <50, or ≥50 g/d), history of hypertension (yes or no), and energy-adjusted quintiles of fiber intake (g/d) and cholesterol intake (mg/d). Age at baseline (y) and the calendar year in which the baseline questionnaire was returned (y) were entered into the model through the strata statement. Within each study, hazard ratios with 95% CIs for the incidence of a coronary event and of mortality from coronary heart disease were calculated by using Cox proportional hazards regression with time in study (y) as the time metric. The study-specific logs of hazard ratios were weighted by the inverse of their variances, and a combined estimate of the hazard ratios was computed by using a random-effects model. The estimated hazard ratios for PUFAs and CHs can be interpreted as the estimated differences in risk of a 5% lower energy intake from saturated fatty acids (SFAs) and a concomitant higher energy intake from PUFAs and CHs, respectively. The squares and horizontal lines represent the study-specific hazard ratios and 95% CIs, respectively. The area of the squares reflects the study-specific weight (inverse of the variance). The diamonds represent the combined hazard ratios and 95% CI. AHS, Adventis Health Study; ARIC, Atherosclerosis Risk in Communities Study; ATBC, Alpha-Tocopherol and Beta-Carotene Cancer Prevention Study; FMC, Finnish Mobile Clinic Health Study; GPS, Glostrup Population Study; HPFS, Health Professionals Follow-Up Study; IIHD, Israeli Ischemic Heart Disease Study; IWHS, Iowa Women's Health Study; NHSa, Nurses' Health Study 1980; NHSb, Nurses' Health Study 1986; VIP, Västerbotten Intervention Program; WHS, Women's Health Study.