What is an optimal diet? Relationship of macronutrient intake to obesity, glucose tolerance, lipoprotein cholesterol levels and the metabolic syndrome in the Whitehall II study

OBJECTIVE: Saturated fats have adverse effects on health. To investigate wh ich is more beneficial for energy replacement, we compare the effects of po lyunsaturated fatty acid and carbohydrate intake on obesity and metabolic v ariables (fasting triglycerides, HDL-cholesterol, LDL-cholesterol and 2 h g lucose). Further, because the optimum diet may differ according to glucose tolerance, we examine the same associations in glucose tolerant and intoler ant groups. Finally, we test the effect of macronutrient intake on the pres ence or absence of the metabolic syndrome. DESIGN: Cross-sectional analysis. SUBJECTS: A total of 4497 men and 1865 women aged 39-62 in the Whitehall II study. RESULTS: In men, higher intakes of both polyunsaturated fats and carbohydra tes were linked to lower waist-hip ratio, triglycerides and LDL-cholesterol . Higher carbohydrate intake alone was linked to decreased body mass index (for 10 g higher carbohydrate intake, -0.12 kg/m(2), P < 0.0001) and lower HDL-cholesterol (-0.01 mmol/l, P < 0.01). in normoglycaemic men, higher car bohydrate intakes were associated with higher 2 h insulin and glucose level s (0.25 pmol/l, P < 0.05 and 0.01 mmol/l, P = 0.001, respectively). Dietary effects among women were similar, the exception being a positive associati on of polyunsaturated fat intake with body mass index and waist-hip ratio ( 0.47 kg/m(2) P < 0.05 and 0.006, P < 0.05, respectively). Dietary component s, with the exceptions of cholesterol and protein in men, were unrelated to prevalence of the metabolic syndrome, and adjustment for differences in ma cronutrient intake did not account for the strong inverse association betwe en socioeconomic position and the metabolic syndrome. CONCLUSION: Our observational data provide evidence that both polyunsaturat ed fatty acids and carbohydrates offer small metabolic benefits with few ad verse effects compared with saturated fats.