Effects of different types of isocaloric parenteral nutrients on food intake and metabolic concomitants

Whether spontaneous food intake (SFI) is controlled by infused nutrient type or its caloric content, irrespective of nutrient type, was investigated. Rats were infused for 4 days with isocaloric solutions of different nutrient type but sharing the same intermediary metabolic oxidative pathway, providing 25% of daily caloric needs. One parenteral solution was a glucose, fat and amino acid mix (TPN-25%); the other provided ketone bodies (TRI-3.5%). Effects of parenteral infusions on SFI and metabolic concomitants were compared and contrasted to that in a group of orally fed rats. Both infusions reduced SFT by 50%. Rats receiving TRI-3.5% had lower blood glucose and insulin concentrations, but increased hepatic glycogen content compared to TPN-25% or orally fed rats. No differences in hepatic triglycerides occurred between the three groups. However, serum free fatty acids were significantly lower in TRI-3.5% and in TPN-25% groups vs. fed rats. Data indicate food intake suppression is mediated by caloric content rather than nutrient type, suggesting that a mediator of SFI regulation could be at the citric acid cycle level.