This preliminary investigation, involving 422 patients, tested the hypothesis that rate of eating is associated with obesity in patients with type 2 diabetes or hyperlipidaemia at all ages. The patients' eating habits were determined using a questionnaire, and the patients were classified as quick, normal or slow eaters. The body mass indices of the three groups were compared. The body mass indices of the male patients who ate quickly (25.4 +/- 0.2 kg/m2) were significantly higher than those of the patients who ate at a normal rate (24.4 +/- 0.3 kg/m2) or slowly (24.1 +/- 0.5 kg/m2). No difference between body mass indices in the female groups was found. It was speculated that rate of eating affects body weight in male patients with type 2 diabetes or hyperlipidaemia.