The present invention relates to methods for reducing fat uptake in the gastrointestinal tract of a mammal in order to prevent a positive energy balance, weight gain, overweight and obesity, and to induce a negative energy balance and weight loss in subjects who wish to reduce their body weight. In particular, food and/or beverage ingredients and dietary supplements of the present invention comprises flaxseeds useful for increasing faeca fat excretion from the gastrointestinal tract.