The effects of age and various fat/carbohydrate caloric ratios on nitrogen retention and wound healing in rats.

Recent reports have indicated a possible age-related component to the ability of various species to utilize either fat or carbohydrate as their preferential energy source. These studies have demonstrated that infant rats given a high-fat diet (50% fat, 35% carbohydrate, 15% protein) retain a significantly higher amount of nitrogen than do infant rats on a high-carbohydrate diet (82% carbohydrate, 3% fat, 15% protein). Conversely, adult rats maintain a higher positive nitrogen balance when given the high-carbohydrate diet. In light of these studies, and our interest in factors that contribute to wound healing in the surgical patient, we investigated the effects of low-, medium-, and high-fat enteral diets on wound healing and nitrogen balance in surgically stressed rats of various ages. Weanling (45 g) and young adult (175 g) male Sprague-Dawley rats (n = 16 per age group) were housed individually in metabolic cages. All animals had Impra vascular-graft wound cylinders placed subcutaneously in the dorsal midline and were placed in four dietary groups: high fat (50% kcal), medium fat (30% kcal), low fat (2.5% kcal), and chow (Purina Standard Laboratory Rodent Chow, 17% kcal as fat). All test diets were isonitrogenous (3.1 g nitrogen/1,000 kcal) and isocaloric for each age group. Animals in each age group were pair-fed (35 kcal/d, weanlings; 60 kcal/d, young adults) for 10 days and then euthanized. Wound cylinders were removed and analyzed for collagen content.(ABSTRACT TRUNCATED AT 250 WORDS)