How much protein is safe?

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Abstract
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? 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. 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. 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.