Summary-Gastrointestinal and Immunologic Development

CARBOHYDRATE DIGESTION AND ABSORPTION Whereas the first session of this meeting was concerned primarily with the nutritional content of infant feeds, the second focused on development of the organs that digest those feeds. Dr Richard Grand began the session with a review of various aspects of the development of the intestine from biochemical and physiologic standpoints, indicating that the absorption of various elements of food is dependent upon enzymatic activity and absorptive capability. He showed that, for unknown reasons, glucose from sucrose is absorbed at a much faster rate than glucose alone. In addition, in contrast to general opinion, the scientific data show that diand tripeptides are absorbed faster and by different mechanisms than the individual amino acids. Grand's talk then focused on the enzymes of the brush border, with particular emphasis on five enzyme groups that are involved in carbohydrate metabolism: (1) glucoamylase; (2) sucrase-isomaltase; (3) maltase; (4) lactase; and (5) trehalase. (The last enzyme is probably of minor importance in present day nutrition.) Grand also indicated that at one week of life, there is a decreased amount of digestibility derived from pancreatic enzymes, particularly amylase. The relationship of these enzymes to nutrition was made quite evident by some studies conducted with the perfused fetal lamb, in which lactose was shown not to be a limiting substrate as there was a sufficient amount of lactase present in the intestine. In contrast, sucrose and maltose contributed little glucose to the general circulation of the lamb because sucrase and maltase were deficient in the intestine.