Ovarian hormone fluctuations predict within-cycle shifts in women's food intake.

What role do ovarian hormones play in modulating day-to-day shifts in women's motivational priorities? In many nonhuman mammals, estradiol causes drops in feeding and foraging, progesterone reverses this effect, and the two hormones in combination produce cycle phase shifts characterized by lower food intake near ovulation when sexual receptivity is at its peak. Hormonal predictors of within-cycle shifts in women's total food intake have not been previously tested. Here, in a study with both daily hormone measures and self-reported food intake, we found that within-cycle fluctuations in estradiol negatively predicted shifts in food intake, progesterone fluctuations positively predicted them, and the two hormones together statistically mediated a significant peri-ovulatory drop in eating. These patterns are precisely opposite to those previously reported for sexual desire from this same sample (i.e. positive and negative effects of estradiol and progesterone, respectively, on desire). To more precisely test endocrine regulation of tradeoffs between sexual and eating motivation, a difference score for the daily standardized values of the sexual desire and food intake variables was created. Fluctuations in estradiol and progesterone were oppositely associated with shifts in this difference score, supporting hormone modulation of tradeoffs between alternative motivational priorities. These tradeoffs were especially pronounced during the fertile window of the menstrual cycle on days when conception was possible, consistent with the hormone effects functioning to shift motivational salience between feeding and mating depending on within-cycle changes in fecundity. The findings provide direct evidence that phylogenetically conserved endocrine signals regulate daily shifts in human motivational priorities.