Influence of parenteral feeding on spontaneous caloric intake and food selection in rats

We compared spontaneous caloric intake (SCI) of rats exclusively receiving chow to SCI of rats given the choice of chow or Parmesan cheese, and then examined the influence of parenteral feeding on SCI and food selection. Six rats in a Chow Diet Group were offered Purina chow for 21 days, while five rats in a Choice Diet Group were offered Parmesan cheese or the same chow. Daily SCI (kcal/day) and body weight gain (BWG; g/day) were determined. Rats in the Choice Diet Group ate twice as much cheese as chow for the first 3 days of the experiment. Thereafter, SCI and BWG became comparable in both groups, with no significant differences for the rest of the study. In another group of nine rats, a central venous catheter was inserted. After 7 days, rats were offered chow and water ad libitum during the infusion of normal saline at 3 ml/hour for 3 days (Saline). Then, normal saline was replaced by a total parenteral nutrition (TPN) mixture of glucose, fat, and amino acid providing 85 kcal/day, and rats were randomized to eat either Chow Diet or Choice Diet. In both groups, SCI during TPN was significantly reduced as compared to the SCI on Saline. However, rats in the Choice Diet Group ate three times more chow than cheese during TPN. We conclude that a) food preference can increase SCI for short periods of time; b) TPN reduces SCI; c) TPN modifies food preference; and d) food preference does not increase SCI during TPN.