OBJECTIVE: To assess the relationships between concern over bodyweight, anthropometric parameters (both real and ideal) and estimated energy balance. DESIGN: Prospective study. SUBJECTS: 126 young, female university students from Madrid, Spain, between the ages of 19 and 36. MEASUREMENTS: Energy intake was measured by means of a 'seven day food record'. Anthropometric data were collected both at the beginning of the study and at 30 d to determine any change in weight. Subjects were grouped with respect to body mass index (BMI) (BMI < 30th percentile, between 30th and 60th percentiles and greater than or equal to 60th percentile). Subjects also completed a questionnaire asking id they would like to lose some weight. RESULTS: The concern of these young women about their body image was greater amongst those with higher BMI. However, 31.6% of subjects with BMI falling < 30th percentile (< 20.1 Kg/m(2)) wished to lose some weight. Though the mean discrepancy between energy intake and estimated energy expenditure was 5.7%, there were great differences with respect to BMI and concern expressed about bodyweight. The declared energy intake was 9.3% greater than estimated energy expenditure in very thin subjects (BMI(30th percentile) who expressed no desire to lose weight. However, in subjects with BMI between the 30th and 60th percentiles and who wanted to lose weight, declared energy intake was 11.4% below estimated expenditure. Similarly in subjects with BMI greater than or equal to 60th percentile, declared energy intake was 15.7% below estimated expenditure. CONCLUSION: In order to gain more exact knowledge of food intake in dietary studies. factors such as subject BMI and desire for a different bodyweight should be taken into account.