How much protein is safe?

BACKGROUND: Since breastfeeding and human milk seem to prevent, while high dietary proteins in the first 2 y of life seem to promote, later overweight, questions have been raised on the safe levels of proteins in the early years. How much protein (as a percentage of total calorie intake) is safe? METHODS: Revision of available data on the protein content of human milk, protein intake in the first 2 y of life and their association with body mass development. RESULTS: We should move from the figure of 7-8% in the 4-month exclusively breastfed infants up to the maximum acceptable levels of 14% in 12-24-month-old infants. When protein supply represents less than 6% and energy is limited, fully breastfed infants are likely to enter a status of negative nutrient balance. Over the limit of 14% energy from proteins in the 6-24 months period, some mechanisms may begin to operate, leading young children towards an early adiposity rebound and overweight development, beyond any genetic predisposition. Preliminary data seem to indicate a causal role for whole cow's milk proteins. CONCLUSION: We suggest maintaining breastfeeding as long as possible, and, in case human milk is insufficient, to introduce infant formulas, appropriate for age, up to 18-24 months, in order to keep protein intakes in the safe range of 8-12% within a diet adequate in energy and balanced as far as macronutrients.