SummaryBackground: It is unclear how dietary intake of the macronutrients such as fats, carbohydrates and proteins affect body composition. Previous studies on how different diets and nutrients influence body composition are usually carried out in the context of weight loss. Little research has been performed on the relation of habitual intake of macronutrients with body composition.Objectives: The relation of macronutrients and other covariates with percent body fat (%BF) and body mass index (BMI) in a general population sample was examined. Differences between lean and BMI-obese or %BF-obese subjects with respect to energy intake, macronutrient composition and other related factors were investigated.Design: A cross-sectional, population-based study of 4478 middle-aged (47-49 y) and elderly (71-74 y) subjects from the Hordaland Health Study was conducted using data from a validated food frequency questionnaire and body composition measurements by dual-energy X-ray absorptiometry. The relation between macronutrient intake and body composition was investigated in the total group and in a subgroup with intermediate and stable BMI over the previous six years (BMI within the 25th-75th percentile and percentage weight change less than ± 5%; n = 975). Results: Using multivariate linear regression analysis in the total population, protein intake was associated with higher %BF and BMI (partial r = 0.11, P < 0.001and partial r = 0.15, P < 0.001, respectively). In the subgroup with intermediate and stable weight, no association was found between protein intake and %BF or BMI whereas fat and carbohydrate intakes were associated with %BF (partial r = 0.07, P = 0.042 and partial r = -0.07, P = 0.042, respectively). Both in the total population and in the weight-stable group, physical activity showed significant inverse effects on adiposity (P < 0.001). There were differences in macronutrient composition and energy intake when comparing BMI-obese or %BF-obese subjects with their leaner counterparts, especially among women.Conclusion: High dietary protein intake may contribute to adiposity in the general population, but in subjects with average and stable weight, fat intake appeared more important. Overall, macronutrient composition did not play a major role for body composition in this population. The best approach for maintaining low degree of adiposity in a healthy population is perhaps through increased physical activity.