Effects of L-phenylalanine on energy intake in overweight and obese women: interactions with dietary restraint status.

L-Phenylalanine (Phe), is a potent releaser of the satiety hormone, cholecystokinin (CCK) and previous studies, conducted primarily in men, show that ingestion of Phe reduces energy intake. The objective of the current study was to test the effects of Phe on energy intake in overweight and obese women. Subjects (n=32) received three treatments (high-dose (10 g Phe), low-dose (5 g Phe and 5 g glucose) or control (10 g glucose)) 20 min before an ad libitum lunch and dinner meal in a within-subjects', counterbalanced, double-blind study. No effect of Phe was found, however, interactions with dietary restraint status were detected in post-hoc analyses. Energy intake over the day was 11% lower following high-dose Phe versus control for women classified in the lower tertile of rigid restraint, a subscale of the dietary restraint scale, whereas no effects were noted for women in the middle and upper tertiles. High-dose Phe increased ratings of nausea, however, reduced energy intake in the high-dose condition was noted only for subjects with low nausea ratings. These results suggest that the satiety response to Phe is modulated by rigid restraint status and that reductions in food intake occur independently of Phe's effects on nausea.

A high-glycemic meal pattern elicited increased subjective appetite sensations in overweight and obese women.

We examined the effects of variations in postprandial glycemia and insulinemia on subjective satiety in overweight and obese women. We altered the ingestion rate of a glucose beverage to model the postprandial effects of high- and low-glycemic meals. Fourteen women were tested in a within-subjects' design with two conditions: (1) Rapid, with a large glucose beverage consumed with breakfast and lunch and (2) Slow, with the same volume of glucose beverage consumed in eight portions (one with each meal, and the remaining seven at 20-min intervals after each meal). Meals were identical in the two conditions. Subjective appetitive sensations were measured with visual analog scales before and after meals, and hourly after each meal until 5 pm. Serum glucose and insulin were measured at similar time points. Subjects reported higher ratings of hunger and prospective consumption in the Rapid versus Slow condition at 4h after breakfast and several hours after lunch. Serum glucose was more strongly correlated with the appetitive ratings in the Rapid than the Slow condition, and explained more of the variance (20-31%) than insulin (2-4%). The results of this study support the glucostatic theory linking dynamic changes in blood glucose with appetitive sensations.