During weight loss, dairy calcium is proposed to accelerate weight and fat mass loss through increased fecal fat excretion. The primary objective was to investigate if a high-dairy energy-restricted diet is superior to low-dairy in terms of changes in body weight, body composition and fecal fat excretion over 24 weeks. Secondary objectives included fecal energy and calcium excretion, resting energy expenditure, blood pressure, lipid metabolism and gut microbiota. In a randomized, parallel-arm intervention study 11 men and 69 women (BMI 30.60.3 kg/m2, age 441 years) were allocated to a 500 kcal (2100 kJ) deficit diet either high (HD: 1500 mg calcium/d) or low (LD: 600 mg calcium/d) in dairy products for 24 weeks. Habitual calcium intake was ~1000 mg/d. Body weight loss (HD: -6.6±1.3 kg, LD: -7.9±1.5 kg, P=0.73), fat mass loss (HD: -7.8±1.3 %, LD: -8.5±1.1 %, P=0.76), changes in fecal fat excretion (HD: -0.57±0.76 g, LD: 0.46±0.70 g, P=0.12) and microbiota composition were similar for the groups over 24 weeks. However, total fat mass loss was positively associated with relative abundance of <i></i>Papillibacter <i></i>(P=0.017) independent of diet group. Consumption of a high dairy diet did not increase fecal fat or accelerate weight and fat mass loss beyond energy restriction over 24 weeks in overweight and obese adults with a habitual calcium intake of ~1000 mg/d. However, this study indicate that <i>Papillibacter</i> is involved in body compositional changes.