Impact of menstrual cycle and hormonal contraception on whole-body protein turnover in recreationally active females.

Protein turnover may be influenced by menstrual cycle hormones and hormones from oral contraceptives (OCs) and hormonal intrauterine devices (H-IUDs), yet data are limited. This study evaluated whole-body protein turnover in 40 healthy, active females (eumenorrheic = 15; OC = 13; H-IUD = 12) tested once in low- and high-hormone phases. Using a [15N]alanine tracer, net protein balance, synthesis, breakdown, and nitrogen flux were measured. No group differences were observed. Protein breakdown and nitrogen flux were higher in the low-hormone phase in the total sample. These small hormone cycle phase-related changes in protein breakdown and nitrogen flux may guide active women's nutrition and exercise strategies.