Diet composition and body mass index in Tehranian adults

Human studies investigating the relationship between macronutrients intake and obesity, have failed to achieve consistent findings. This study was undertaken to assess the relationship between macronutrients intake and body mass index in a group of Tehranians. From 15,005 participants of the Tehran Lipid and Glucose Study, 1290 subjects aged over 10 years (565 males and 725 females) were selected randomly for dietary survey. Anthropometric indices were measured according to standard protocols and BMI was calculated. Dietary data were collected by trained interviewers using two non-consecutive 24-hour dietary recalls. Data on smoking habits, educational level and physical activity were compiled. Under- and over-reporting of energy intake were defined as EI: BMR < 1.35 and > or = 2.4, respectively. Calorie-adjusted amounts of macronutrients were calculated by the residual method, following which energy intakes from all calorie-adjusted macronutrients were simultaneously included in the multiple regression models controlling for age, physical activity, educational level and smoking and mutual effects of macronutrients. Total energy intake was not included to avoid collinearity. BMI increased with age in either gender. Controlling for confounding variables, energy intake from fat was positively associated with BMI in males in the 10-18, 19-24, 25-50 and 51+ year age categories (beta = 0.06, 0.13, 0.33, 0.48, P<0.05 for all, respectively) and females in the 19-24, 25-50 and 51+ age categories (beta = 0.17, 0.43, 0.52, P<0.05 for all, respectively). This relationship remained after excluding misreporters (beta = 0.06, 0.15, 0.36, 0.50 for males and beta = 0.21, 0.46, 0.54 for females in the corresponding age categories, respectively). The correlation of fat intake to BMI was not significant in younger females (10-18 year). No association was seen between energy intake from protein and carbohydrate with BMI in subjects before and after exclusion of misreporters. In conclusion, energy from fat was found to be independently and positively associated with obesity in adults. No other association was observed between energy from protein and carbohydrate with BMI.