Effects of soy foods on urinary sex steroid excretion and metabolic and cognitive health: The plants optimizing development study (PODS) protocol

Soy foods are a dietary source of high-quality protein, essential micronutrients, and isoflavones with the potential to contribute to numerous health benefits. Previous research has examined the effects of soy isoflavones on health in adults, but comparatively little is known regarding the health effects of isoflavones in childhood. The Plants Optimizing Development Study (PODS) seeks to address this significant research gap. Children (N = 96) between the ages of 8–11 years will be recruited to participate in a 3-month randomized-controlled clinical trial. Treatment group participants will receive daily, a mix of soy foods with the target total isoflavone (i.e., daidzein, genistein, and glycitein) intake of 50 mg/d. The control group will consume isocaloric soy-free alternatives. The primary outcomes are sex steroids excreted in urine. Secondary outcomes include Android:Gynoid fat ratio, bone mineral density (BMD), blood lipids and fasting glucose, fecal microbial α-diversity, β-diversity, microbial taxa relative abundance, and cognition. Dual-energy X-ray absorptiometry will assess BMD and Android:Gynoid fat ratio. Urine samples will be analyzed for sex steroids using Liquid chromatography-mass spectrometry and adjusted for urinary creatinine. Stool and venous blood samples will assess gut microbiota and metabolic marker analyses, respectively. Cognitive assessments will include the Woodcock-Johnson Tests of Cognitive Abilities and Academic Achievement IV, a spatial memory task, and a modified Eriksen flanker task. The central hypothesis is that greater soy isoflavone consumption will not alter sex steroid levels but will be associated with beneficial outcomes on body composition, metabolic health, and the gut-brain axis in pre- and early adolescents.