Ovarian function is examined in 35 Lese women inhabiting the Ituri Forest of northeastern Zaire over a period of 4 months through measurements of progesterone in saliva samples collected twice weekly. Ovulatory frequency is found to be only 56% on average, with a pattern of age variation similar to that observed in western women, though lower in level at each age. Average luteal progesterone levels of the Lese women are lower than those of Boston controls even if only ovulatory cycles are considered. Women with the poorest nutritional status, inferred from longitudinal weight changes and weight for height, show the greatest compromise of ovarian function, and the average ovulatory frequency of the whole sample declines in parallel with a period of weight loss over four months. It is suggested that low ovulatory frequency and luteal insufficiency contribute to the low fecundity of the Lese population and that nutritional status is likely to be one of the ecological factors modulating this effect.

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The effects of moderate, voluntary weight loss on ovarian function are studied by monitoring the daily levels of salivary progesterone in 8 dieting women (18 cycles) and 9 age-matched controls (19 cycles). Both groups of women were within normal standards of weight for height, though the dieters were significantly heavier than the controls. Dieters lost weight at an average rate of 1.9 ± 0.3 kg/mo during the study. Dieters' cycles during periods of weight loss (weight loss cycles) have significantly lower peak levels of luteal progesterone (controls 655 ± 46 pmol/L, weight loss 461 ± 67 pmol/L; P < 0.005) and lower average levels of luteal progesterone (controls 287 ± 30 pmol/L, weight loss 214 ± 23 pmol/L; P < 0.005) than do controls. All control cycles were classified as ovulatory by virtue of at least one salivary progesterone reading ≥ 300 pmol/L. Only 62% of the weight loss cycles were classified as ovulatory by this criterion. Where longitudinal weight data are available both the magnitude and duration of progesterone elevation correlates significantly with net weight change during the preceding cycle and show no significant correlation with net weight change during the current cycle. Examination of individual profiles confirms that the most profound suppression of luteal activity usually occurs during post-loss rather than weight loss cycles, even if weight is stable or increasing during the post-loss cycle itself. These results, together with field studies of African horticultural populations, suggest that human ovarian function may be adapted to modulate waiting time to conception in response to trends in energetic balance.

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