Effects of Long-Term Walnut Consumption on Body Composition in the Walnuts and Healthy Aging (WAHA) Randomized Clinical Trial

Background and Objectives: Walnuts have recognized health benefits but are fat-rich, raising the concern that regular consumption might increase adiposity. We investigated whether long-term walnut consumption is associated with changes in body composition. Subjects and Methods: The Walnuts And Healthy Aging (WAHA) study is a 2-year, two-center (Barcelona, Spain; Loma Linda, California), randomized controlled trial designed to assess the effects of walnuts on age-related health outcomes. Healthy older adults (63–79 years) were assigned to either a walnut-supplemented diet (15% daily energy) or a control diet (no walnuts). Changes in body weight, BMI, and total fat and fat-free mass, measured by dual-energy X-ray absorptiometry, were pre-specified endpoints. Other body composition variables were secondary endpoints. Changes in circulating leptin and adiponectin and effect modification by obesity-linked variants at the FTO and APOE gene loci were exploratory outcomes. Results: We included 326 participants (220 women) from the Barcelona node. After 2 years, total and android fat mass increased, whereas gynoid fat mass and fat-free mass decreased irrespective of sex and group allocation. There were no effects of walnut vs. control diets on any endpoints, except for a small increase of the android/gynoid ratio in women. On the walnut but not the control diet, men with the CC genotype for the FTO-rs1861868 C > T polymorphism disclosed adverse body composition changes compared to T-allele carriers. However, sample size was small. Effects did not vary by APOE genotype. Conclusions: Two-year walnut consumption had little effect on body composition in older adults. Genetic variability at FTO may modulate the response. The results support the overall harmlessness of walnuts regarding adiposity.