Abstract
Controversy exists in the literature regarding the effect of parenteral nutrition on appetite. Earlier, several authors showed that healthy adult males receiving IV nutrition reduced their voluntary food intake by an amount that approximated 80% of the IV calories. 1 This finding suggested a postabsorptive control of oral food intake. In view of this observation, the authors of this study sought to answer two questions: does parenteral nutrition decrease gastric emptying and does the administration of branched-chain amino acids (BCAAs) alter the rate of gastric emptying?
Nine healthy male volunteers between the ages of 20 and 31 years with a mean weight of 72 ± 10 kg were studied. Basal energy requirements were calculated using the Harris-Benedict equation and were estimated to be approximately 1765 kcal/d. All subjects were maintained on a diet consisting solely of an oral liquid supplement composed of 40% carbohydrate, 20% protein, and 40% fat (Ensure, Ross Labs, Columbus, OH). Each subject served as his own control and was studied three times. The first 6 days of each study period were spent at home consuming the oral liquid supplement. On the sixth day, subjects were admitted to the hospital, and after an overnight fast, one of three parenteral solutions was infused over a 12-hour period. The parenteral formulas consisted of Ringer's lactate, a standard parenteral solution, or a parenteral solution in which half of the amino acids used in the standard parenteral solution were replaced with BCAAs. The latter two formulas consisted of 40% carbohydrate, 20% protein, and 40% fat and supplied 85% of the subjects' estimated basal energy needs. After 6 hours of the parenteral infusion, subjects consumed 500 mL of technetium-labeled Ensure within a 2-minute period, and gastric emptying was then measured by scintigraphy. In addition, blood samples were drawn 5 hours after initiation of the IV infusion and 45 minutes after consumption of the oral supplement for analysis of plasma glucose, insulin, glucagon, triglyceride, and free fatty acid levels.
The rate of gastric emptying within the first 10 minutes after ingestion of the oral supplement was most rapid when Ringer's lactate was infused (radioactivity lost from stomach was 1.63%/min). The rate slowly decreased over the subsequent 50 minutes until it reached a steady rate of 0.46%/ min. The initial rate of gastric emptying was significantly slower with the standard parenteral formula (0.67%/min) compared with the Ringer's lactate. However, the rate was not significantly different than that of the Ringer's lactate after 50 minutes (0.48%/min). The initial gastric emptying rate during infusion of the BCAA solution (0.83%/min) was between that of the Ringer's lactate and the standard parenteral solution. Fifty minutes after infusion of the BCAA solution, the rate decreased to 0.43%/min; this rate was slightly lower than that observed with the other two IV solution at this time point (Table I). Mean serum glucose levels never exceeded 122 mg/ dL, and there was no correlation between glucose concentrations and the rate of gastric emptying. There were no significant changes in free fatty acid or plasma glucagon concentrations.
These results demonstrate that gastric emptying is delayed in normal healthy male subjects receiving 42.5% (~750 kcal) of their estimated basal energy requirements from parenteral nutrition over a 6-hour period. In addition, the authors propose that the BCAA parenteral solution did not delay gastric emptying to the same degree as the other two parenteral solutions due to the ability of BCAAs to decrease serotonin synthesis in the brain. Serotonin is a neurotransmitter known to regulate food intake and inhibit gastric emptying. Thus the authors suggest that providing parenteral solutions enriched with BCAAs may improve voluntary food intake during and after parenteral nutrition administration. They conclude that the reduction in oral intake frequently seen in patients receiving parenteral nutrition may be a reflection of the parallel reduction in the rate of gastric emptying rather than a result of existing disease.
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