Two studies were conducted to compare characteristics of consumers and non-consumers of vitamin and/or dietary supplements (study 1) and to assess the effect of a multivitamin and mineral supplementation during a weight-reducing programme (study 2). Body weight and composition, energy expenditure, and Three-Factor Eating Questionnaire scores were compared between consumers and non-consumers of micronutrients and/or dietary supplements in the Québec Family Study (study 1). In study 2, these variables and appetite ratings (visual analogue scales) were measured in forty-five obese non-consumers of supplements randomly assigned to a double-blind 15-week energy restriction ( - 2930 kJ/d) combined with a placebo or with a multivitamin and mineral supplement. Compared with non-consumers, male consumers of vitamin and/or dietary supplements had a lower body weight (P < 0.01), fat mass (P < 0.05), BMI (P < 0.05), and a tendency for greater resting energy expenditure (P = 0.06). In women, the same differences were observed but not to a statistically significant extent. In addition, female supplements consumers had lower disinhibition and hunger scores (P < 0.05). In study 2, body weight was significantly decreased after the weight-loss intervention (P < 0.001) with no difference between treatment groups. However, fasting and postprandial appetite ratings were significantly reduced in multivitamin and mineral-supplemented women (P < 0.05). Usual vitamin and/or dietary supplements consumption and multivitamin and mineral supplementation during a weight-reducing programme seems to have an appetite-related effect in women. However, lower body weight and fat were more detectable in male than in female vitamin and/or dietary supplements consumers.