The loss of weight was analysed in a group of sixty overweight/obese women of childbearing age (20–35 years) according to their initial vitamin D status. Subjects were randomly assigned to one of two slightly hypocaloric diets: Diet V, in which the consumption of vegetables was increased, or Diet C, in which the relative consumption of cereals (especially breakfast cereals) was increased. Dietetic, anthropometric and biochemical data were collected at the start of the study and again at 2 weeks after dividing the women into groups depending on their having an initial serum 25-hydroxyvitamin D (25(OH)D) concentration of < 50 nmol/l (LD) or ≥ 50 nmol/l (HD). Dietary intervention led to a reduction in energy intake, body weight and BMI in all groups. The HD women showed greater body fat losses during the study than the LD women (1·7 (sd 1·8) kg compared to 0·5 (sd 0·8) kg). A better vitamin D status therefore aided the loss of body fat over the experimental period (OR 0·462; CI 0·271, 0·785; P < 0·001). However, when the dietary groups were analysed separately, this effect was only seen in the C subjects (OR 0·300; CI 0·121, 0·748; P < 0·001). The present results suggest that women with a better vitamin D status respond more positively to hypocaloric diets and lose more body fat; this was especially clear among the C subjects who had a greater vitamin D supply during the experimental period.