The complex process of digestion/absorption can be optimally effective only when the GI tract and accessory organs are totally develop and fully functioning. The primary function of the GI tract is the digestion and absorption of nutrients.
Not only must the muscular tube (alimentary canal) with it a mucosal lining and endocrine cells be operating efficiently in conjunction with the nervous system, but the accessory organs (pancreas, liver, and gallbladder) with their important digestive secretions also must be physiologically mature.
Normally, the initial breakdown or hydrolysis of carbohydrates depends on both salivary and pancreatic amylase. However, in the infant, carbohydrate hydrolysis is limited by the fact that although salivary amylase is present by 34 weeks’ gestation, secretion of pancreatic amylase does not begin until age 4 to 6 months.
The feeding of infants is based on primarily in degree of maturation of the GI tract and accessory organs. Good examples of the emphasis on GI tract maturity are the care given to the fat in infant formula and the time and sequence of the introduction of various foods into the infant’s diet.
Only those fats possessing an ease used in commercial formulas and the introduction of solid food, beginning with baby cereal usually occurs no earlier than 4 months of age. The absorption coefficient of fats is 90 to 95% during the first week of life and at least 96% at 1.5 months of age.
The infant pancreas, although structurally mature at term, is usable for several months to produce enzymes sufficient for effective digestion.
Digestion and absorption at infant age