Newborn are limited in their ability to digest and absorb certain nutrients due to decreased activity of specific enzymes and other substances as well as functional and anatomic limitations.
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 gastrointestinal (GI) system is a complex organ system that extends from the mouth to the anus and includes the esophagus, stomach, small and large intestines, liver, and pancreas.
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.
The secretion of gastric, intestinal and pancreatic digestive enzymes is not developed to adult levels in young infants.
Nevertheless, the infant is able to digest and absorb the nutrients in human milk fully and efficiently and breast milk contains enzymes that contribute to the hydrolysis of fat, carbohydrate and protein in the gut.
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.
The infant pancreas, although structurally mature at term, is usable for several months to produce enzymes sufficient for effective digestion.
Pancreatic lipase, alpha-amylase and the proteolytic enzymes are in too short supply to accommodate digestion of a mixed diet. Digestion of fat is a real concern due to decreased levels of bile salts from the liver as well as low lipase release from the pancreas.
Bile salt low because of decreased syntheses and decreased intestinal reabsorption. While fetal lipase levels are detected at 21 weeks gestation, but do not reach adult concentrations until 6 months of age in the term infant.
Digestion and absorption of fat during infant stage
