High-fat semielemental diet in the treatment of protracted diarrhea of infancy. The capacity for greater fat absorption relative to carbohydrate absorption in protracted diarrhea of infancy was studied in a developed and a developing country (Buffalo, NY, and Bangkok, Thailand). Fifty patients with protracted diarrhea in the first year of life (defined as liquid stools of more than 20 mL/kg per day with more than a 14-day duration) were randomly assigned to receive either a standard semielemental diet (Pregestimil) or a high-fat semielemental diet that contained 40% more fat. The increased fat was largely in the form of medium-chain triglycerides, with the new diet providing 60% of the fat as medium-chain triglycerides compared with 40% in the standard diet. Tolerance to both diets was good in both studies. Both groups showed adequate weight gain and an improvement in anthropometric and biochemical parameters. The patients receiving the high-fat diet showed no initial weight loss, however, and their weight gain was initiated earlier. Cumulative weight gain was also higher in the group receiving the high-fat semielemental diet. Fecal fat analyses were performed after 1 week of therapy. There was no difference observed in the coefficient of fat absorption between the groups receiving the two formulas, indicating that infants with protracted diarrhea may be able to tolerate a higher fat intake than is normally provided. As carbohydrate intolerance is known to be a complicating factor when using semielemental enteral feeds for infants with protracted diarrhea, a higher-fat semielemental diet may be the most appropriate way to provide adequate caloric intake. 