Nutrient density in complementary feeding of infants and toddlers.

The paradigm of the first 1000 days of life, the period from conception to the second birthday, has been advanced as a critical window of opportunity to save a life and a child's future. Infancy and toddler life, through the first 24 months after birth, is a unique period during which human milk is recommended as either the exclusive source of nutrition (6 months) or a variable component thereof. After the maternal delivery of milk is accounted for, the remainder of the energy and nutrients needs come from complementary foods. There is an intrinsic gap left by the maternal milk supply in volume and micronutrient content in relation to expanding infant and toddler needs. The nutrient density approach provides us with a mathematical framework to manage the closing of the nutrient gap. The intrinsic nutrient content of the unprocessed foods appropriate for young children is limited. The most problematic nutrients are calcium, iron and zinc. Some manner to enhance the nutrient density of the complementary foods is an incontestable necessity. The nutrient density consideration, which identifies for us the nature of the problem, offers a tool for the titrating of the fortification to an adequate--but safe--addition.