Nutrition, protein turnover, and physical activity in young women.

The whole body protein synthesis rate was measured in four groups of young women by giving a single pulse of 15N glycine and determining the 15N enrichment in the urinary ammonia excreted over the next 10 h. The groups were: Ia, normals, with normal dietary intake; Ib, competition swimmers, normal intake; IIa, normal activity but low intake; and IIb, high physical activity, low intake. The results indicated that the protein synthesis rate was lower in the two low intake groups. It did not correlate with a program of vigorous physical activity, while physical activity, but not nutritional status or the protein synthesis rate correlated with menstrual cycle irregularities.