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 (28–56g) 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 35g during the walnut-supplemented diet. The walnut-supplemented diet resulted in greater daily energy intake (557kJ (133kcal)), which should theoretically have led to a weight gain of 3·1kg 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/m2), 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/m2). 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.
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