Determinants of lactose digestion in the miniature pig.

Although lactose is an important nutrient in the diet of the infant and child, the factors contributing to its digestion have not been clarified adequately. We sought to determine the degree to which lactase activity and small intestinal transit explain lactose digestion, the average error (SEE) in estimating lactose digestion using these parameters, and the effect of age. We compared lactose digestion from both a 7% lactose-containing formula and a solution by determining lactose in ileostomy output in pig littermates at 10 days, 4 weeks, and 10 weeks of age. The entire small intestinal mucosa was assayed for lactase specific activity (micromol x min-1 x g protein-1), total activity (micromol x min-1), and whole-villus lactase activity. Transit time (min), and transit rate (cm/min) were measured. Meal type did not affect lactose digestion. Lactose digestion was explained best by lactase specific activity (formula, R2 = 0.73, SEE = 1.1; solution, R2 = 0.69, SEE = 1.0; P < 0.001). The next best parameter was total transit rate (formula, R2 = 0.69, SEE = 2.0; solution, R2 = 0.46, SEE = 1.3). The relationship with lactase specific activity was age related and there appeared to be a critical value of lactase specific activity above which essentially all the lactose was digested.