Scientific Study

Studies consistently show the beneficial effects of eating nuts; but as high-energy foods; their regular consumption may lead to weight gain. We tested if daily consumption of walnuts (approximately 12 % energy intake) for 6 months would modify body weight and body composition in free-living subjects. Ninety participants in a 12-month randomized cross-over trial were instructed to eat an allotted amount of walnuts (28-56 g) during the walnut-supplemented diet and not to eat them during the control diet; with no further instruction. Subjects were unaware that body weight was the main outcome. Dietary compliance was about 95 % and mean daily walnut consumption was 35 g during the walnut-supplemented diet. The walnut-supplemented diet resulted in greater daily energy intake (557 kJ (133 kcal)); which should theoretically have led to a weight gain of 3.1 kg over the 6-month period. For all participants; walnut supplementation increased weight (0.4 (se 0.1) kg); BMI (0.2 (se 0.1) kg/m(2)); fat mass (0.2 (se 0.1) kg) and lean mass (0.2 (se 0.1) kg). But; after adjusting for energy differences between the control and walnut-supplemented diets; no significant differences were observed in body weight or body composition parameters; except for BMI (0.1 (se 0.1) kg/m(2)). The weight gain from incorporating walnuts into the diet (control-->walnut sequence) was less than the weight loss from withdrawing walnuts from the diet (walnut-->control sequence). Our findings show that regular walnut intake resulted in weight gain much lower than expected and which became non-significant after controlling for differences in energy intake.