No abstract

L‐Phenylalanine (Phe), an essential amino acid, has been shown to elicit release of the gut hormone cholecystokinin (CCK) and reduce energy intake. Animal studies have demonstrated potentiation of the satiety effects of CCK by estradiol (E2). The aim of our study was to compare the effects of Phe on food intake in the follicular phase of the menstrual cycle, when E2 concentrations are high, versus the luteal phase, when the effects of E2 are antagonized by progesterone. In a 2 X 2, within‐subjects' design, 16 women completed four test sessions scheduled to coincide with the follicular and luteal phases of two menstrual cycles. Subjects received Phe in one cycle and placebo in the other. Ad libitum food intake at meals and evening snack was measured. An interaction of condition and phase was found for energy intake at evening snack (P = 0.009). Subjects ate 36% less in the Phe condition versus placebo in the follicular‐phase sessions, but ate the same amount during the luteal‐phase sessions for Phe and placebo conditions (0% reduction). A similar pattern was noted for total daily energy intake although the difference was not statistically significant (P = 0.12) and the effect was smaller (12% reduction with Phe during the follicular phase and 4% reduction during the luteal phase). In conclusion, this study demonstrates that phase of the menstrual cycle modulates the satiety effects of Phe in women. Supported by UB 2020 Scholars Fund.