Clinical studies have shown that the consumption of coffee mannooligosaccharides (MOS) decreases body fat, suggesting that MOS consumption may be useful for weight management. This study was undertaken to determine whether consumption of coffee MOS improves body composition when consumed as part of a weight-maintaining diet. In this double-blind, randomized, placebo-controlled study, 54 men and women, age 19-65 y and with BMI of 27-33 kg/m(2), consumed study beverages twice daily, for 12 wk. Beverages were identical except for the presence (MOS group) or absence (placebo group) of MOS (4 g/d). Body composition was assessed at baseline and endpoint using magnetic resonance imaging (MRI). Body weight, blood pressure, and assessments of feelings of appetite and satiety were taken weekly. Fifty men and women completed both baseline and endpoint MRI scans. There was a significant beverage x time interaction on total body volume (P = 0.026), total adipose tissue (TAT) (P = 0.046), and total subcutaneous adipose tissue (P = 0.032) in men but not women. Men consuming the MOS beverage had a greater percent change in total body volume (P = 0.043) and tended to have greater percent changes in subcutaneous (P = 0.069) and TAT (P = 0.098) compared with the placebo group. Consumption of a MOS-containing beverage, as part of a free-living weight-maintaining diet, leads to reductions in total body volume, relative to placebo, in men. More research is needed to further investigate the mechanism by which MOS may act to improve body composition and to elucidate the influence of gender.