Fatty acids are the major constituent of many lipids, and those which are essential must be provided through the infant diet for a healthy growth, neurodevelopment, immune system, and gastrointestinal function. During the first months of life, especially polyunsaturated fatty acid (PUFAs) requirements are increased, because of rapid growth and neurological development. Fat intake in infants, which is high during the breastfeeding period, is reduced gradually in the second half of the first year from the start of complementary feeding. Fats nutritional requirements of the total daily energy intake, from 0 to 6 months of life are 50–55%, from 6 to 12 months 30–40%, and from 12 to 36 months 35–40%. Recently, different European Organisms have established that the intake of the PUFAs named linoleic acid should constitute 4% of total energy, whereas alpha linolenic acid 0.5% of total energy. Two other long-chain PUFAs named DHA (docosahexaeboic acid) and ARA (arachidonic acid) have a key role in cognitive functions. The European Food Safety Authority (EFSA) has established as adequate DHA intake 100 mg/day from 0 to 24 months of age, whereas the ARA requirements are 140 mg/day from 0 to less than 6 months of age. On the other side, fats’ research efforts have suggested that milk fat globule membrane represent a bioactive fraction of breast milk fat that provide some of its health benefits. This membrane fraction can also be found in cow’s milk fat and is composed of different bioactive components (phospholipids, cholesterol and cerebrosides…), which positively influence brain development and immune functions and protect neonatal gastrointestinal tract modulating gut microbiota composition.
Proteins are important during the first 1000 days of life because their role in cellular structure and as components of enzymes and neurotransmitters. During the first 6 months of age, proteins recommendations per kg body weight/day are: from 0 to 6 months of life 0.58 g and from 6 to 36 months of age, 0.66 g. Human milk has over 400 proteins with a variety of functions, such as antimicrobial, immunomodulatory activities, or stimulation of nutrient absorption. Protein deficiency can lead to poor growth outcomes and delayed motor and cognitive development. However, high protein intake is known to induce a faster weight gain during infancy and correlate with obesity later in life.
The total carbohydrate requirements of the total daily energy intake during the first 6 months of life are 40–45%, from 6 to less than 12 months 45–55%, and from 12 to less than 36 months of age 45–60%, just like adults. Glucose has a key role for an adequate functioning of the central nervous system, because it is the main energy source for growth, nerve impulses, and synapses. Glucose is provided to the baby by different carbohydrates such lactose, as the main sugar present in human milk (ranging from 6.7 to 7.8 g/dl), and a diversity of oligosaccharides, which comprise approximately 1 g/dl. Human milk oligosaccharides constitute a significant fraction of breast milk carbohydrate indigestible by the infant and thus have prebiotics function, nourishing the gut microbiota.