Gastrointestinal Response to Nutrient Variation of Defined Formula Diets

The gastrointestinal response to oral alimentation of low residue commercial defined formula diets or a rat liquid formula was studied. Male Sprague-Dawley rats (220-250 g) were fed isocaloric amounts (73 kcal/day) of Vivonex (V), Vivonex HN (VHN), Flexical (F), Vital (Vit), or a control Casein diet 116EC (C). Nitrogen (N) retention was calculated from N intake minus N excretion/day. After 2 weeks, rats were killed and the liver, pancreas, and small bowel removed and weighed. Pancreatic amylase activity (U g) and liver lipid were measured. The bowel was divided into eight equal segments, and mucosal weight, DNA, and protein concentration per centimeter were measured. Despite isocaloric feeding, body weight gain was lower in V and VHN groups, and higher in F and Vit groups compared to the C. Amylase specific activity was increased in V, VHN, and F groups, while the liver lipid was increased in the V and VHN groups when compared to C animals. The most proximal intestinal segment weight, mucosal weight, protein and DNA of V, VHN, and Vit groups were less than C animals, while distal segments were similar. F animals showed greater intestinal mass than C rats. These studies indicate statistically significant differences in gastrointestinal responses as a result of nutrient variation of defined formula diets.