Despite of a deficient diet with inadequate nutrient intake, women are capable of producing milk in appropriate quantity and quality that may be enough to maintain growth and health of their children. However, it would suppose a risk for depletion of their nutritional reserves and damaging their health.Moreover, well-nourished mothers compared to malnourished, they have a greater daily volume of milk and a slight increase in protein, fat and calories per 100 ml of milk, so the chance of raising a healthy child is higher. There is controversy on whether postpartum weight loss is greater or the return to pre-pregnancy weight is faster in lactating mothers than in non-lactating mothers.Many nursing women lose half a kg per month during the first months, but some do not lose or even gain weight. Slow weight loss (less than 1.5 kg per month) through a balanced diet with at least 1800 calories or no less than 15% of the recommended one together with moderate aerobic exercising is safe for the mother and the infant.Prolactin levels increase under conditions of negative energy balance, which ensures the production of milk and hence protects the infant’s nutrition. It is unknown whether a low calorie diet may affect milk production during the first three postnatal weeks, so any kind of diet over this period is not warranted.