DR. VIRGINIA J. VITZTHUM, Institute of Primary and Preventative Health Care, Binghamton University, Binghamton, New York, was awarded a grant in May 2006 to aid research on 'Testing Hypotheses of the Dietary Determinants of Ovarian Hormones: A Comparative Study of Three Populations.' This research is part of a larger project to elucidate the ecological, behavioral, and ontogenetic determinants of variation in women's reproductive functioning. This phase of the project evaluated the relative importance of total caloric intake versus dietary fat consumption in determining ovarian steroid variation by comparing hormone levels in nomadic-herding Mongolian women (high fat/low calorie diets) with those in previously collected samples of agropastoral Bolivian women (low fat/low calorie diets) and Chicago women (high fat/high calorie diets). Daily biological samples spanning a menstrual cycle and data on covariates were collected from 40 nomadic Mongolian women during July through September 2006. Assays were conducted in collaboration with Dr. Tobias Deschner at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. Initial analyses suggest that ovarian steroid levels are at least as high as those of U.S. women, suggesting that dietary fat may be the more important factor. In addition to increasing current understanding of the sources of variation in ovarian functioning, this finding suggests that the modulation of reproductive functioning during a woman's lifespan may be sensitive to variation in dietary fat intake. Ongoing research includes the collection of a comparative sample of German women and planned research includes genetic analyses to ascertain the potential contribution of genotypic variation to hormonal variation.