Effects of L-Phenylalanine on Energy Intake and Glycaemia—Impacts on Appetite Perceptions, Gastrointestinal Hormones and Gastric Emptying in Healthy Males
What this study found
Overall, 10 g L-phenylalanine produced the clearest acute effects: it reduced buffet energy intake, increased fullness, raised plasma CCK, and lowered postprandial glucose after the mixed-nutrient drink. Energy intake was 900 ± 78 kcal with 10 g versus 1084 ± 76 kcal with control (p = 0.005; 10 g vs control p = 0.012), and CCK AUC -31 to -1 min increased to 135 ± 6 versus 121 ± 5 with control (p = 0.002). Both 5 g and 10 g increased insulin and glucagon, while GLP-1 and gastric emptying were not significantly changed. The 5 g dose showed little or no effect on appetite intake or glycaemia.
- Study & population
- Randomized, double-blind, crossover study in healthy, lean adult males at the Clinical Research Facility, University of Adelaide, Australia.
- Intervention
- L-phenylalanine was administered as an intragastric bolus at doses of 5 g or 10 g via nasogastric catheter in a 100 mL suspension.
- Key limitation
- The study was small, acute, and conducted in a single center in healthy lean men only, limiting generalizability to women, people with obesity, or patients with diabetes.
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Open PDFOriginal abstract
In humans, phenylalanine stimulates plasma cholecystokinin (CCK) and pyloric pressures, both of which are important in the regulation of energy intake and gastric emptying. Gastric emptying is a key determinant of postprandial blood glucose. We evaluated the effects of intragastric phenylalanine on appetite perceptions and subsequent energy intake, and the glycaemic response to, and gastric emptying of, a mixed-nutrient drink. The study consisted of two parts, each including 16 healthy, lean males (age: 23 ± 1 years). In each part, participants received on three separate occasions, in randomised, double-blind fashion, 5 g (Phe-5 g) or 10g (‘Phe-10 g) L-phenylalanine, or control, intragastrically, 30 min before a standardised buffet-meal (part A), or a standardised mixed-nutrient drink (part B). In part A, plasma CCK and peptide-YY (PYY), and appetite perceptions, were measured at baseline, after phenylalanine alone, and following the buffet-meal, from which energy intake was assessed. In part B, plasma glucose, glucagon-like peptide-1 (GLP-1), insulin and glucagon were measured at baseline, after phenylalanine alone, and for 2 h following the drink. Gastric emptying of the drink was also measured by 13C-acetate breath-test. Phe-10 g, but not Phe-5 g, stimulated plasma CCK (p = 0.01) and suppressed energy intake (p = 0.012); energy intake was correlated with stimulation of CCK (r = −0.4, p = 0.027), and tended to be associated with stimulation of PYY (r = −0.31, p = 0.082). Both Phe-10 g and Phe-5 g stimulated insulin and glucagon (all p < 0.05), but not GLP-1. Phe-10 g, but not Phe-5 g, reduced overall plasma glucose (p = 0.043) and peak plasma glucose (p = 0.017) in response to the mixed-nutrient drink. Phenylalanine had no effect on gastric emptying of the drink. In conclusion, our observations indicate that the energy intake-suppressant effect of phenylalanine is related to the stimulation of CCK and PYY, while the glucoregulatory effect may be independent of stimulation of plasma GLP-1 or slowing of gastric emptying.