Calcium from dairy sources is beneficial to weight loss; however, no studies have compared the effects of dairy to nondairy sources of calcium on weight loss. This pilot study explored differences between soy and skim milk on changes in anthropometric values in premenopausal women. In a prospective randomized controlled trial, 14 women with overweight/obesity were randomly assigned to 720 mL soy milk (n=7) or an equivalent volume of skim milk (n=7) daily for 8 weeks. Subjects followed a 500-kcal deficit diet based on metabolic rate data. There were no anthropometric differences between soy and skim milk groups at baseline. Subjects followed an energy-restricted diet; both groups experienced reductions in kilogram weight (4.27+/-2.05 vs 3.76+/-2.25; P=0.668), body fat percent (1.30+/-1.37 vs 1.87+/-1.45; P=0.464), and abdominal circumference (11.28+/-5.23 vs 8.66+/-2.51; P=0.259) while attenuating losses of fat-free mass (1.12+/-1.29 vs 0.43+/-1.12; P=0.299) during the 8-week study. There were no significant differences in weight, fat percent, abdominal circumference, and fat-free mass between groups. To optimize the weight loss effects of calcium, one can consume 720 mL of either soy milk or skim milk daily.