Vitamin K is effective in counteracting (1) increase of body weight and body mass index (BMI), (2) accumulation of body fat mass and (3) accelerates weight loss during calory restriction or other life style interventions aiming weight reduction. A pharmaceutical composition or nutritional formulation comprising vitamin K is provided which can be used to combat overweight or obesity, either as a single, dedicated product or in combination with other slimming products or life style changes.