Diets High in Fiber and Vegetable Protein Are Associated with Low Lumbar Bone Mineral Density in Young Athletes with Oligoamenorrhea

BackgroundAssociations of bone mineral density (BMD) with specific food components, including dietary fiber and isoflavones (that have a negative association with serum estrogen), are unclear and need to be determined, particularly in populations more likely to consume large amounts of these nutrients (such as young athletes).ObjectiveTo determine dietary intake of specific food components in athletes with oligoamenorrhea (OA) compared to athletes with eumenorrhea (EA) and nonathletes (NA), and associations of the dietary intake of these nutrients with lumbar spine BMD.Design and subjectsThis cross-sectional study evaluated 68 OA, 24 EA, and 26 NA individuals aged 14 to 23 years. Measurements included 4-day food records, a dual x-ray absorptiometry scan evaluating lumbar spine BMD and body composition, and hormone levels. Multivariate analysis was used to estimate associations of nutrients with lumbar spine BMD.ResultsCompared with EA and NA, OA had higher intake of fiber, phytic acid, and vegetable protein (all P values <0.0001). Intake of isoflavones, genistein, and daidzein was higher in OA than NA (P=0.003 and P=0.0002, respectively). OA had lower consumption of energy from saturated fatty acids than NA (P=0.002). After controlling for confounders such as body weight, menstrual status (indicative of estrogen status), calcium intake, and serum vitamin D (known BMD determinants), lumbar spine BMD z scores were inversely associated with dietary fiber (β=–.30; P=0.01), vegetable protein (β= –.28; P=0.02), phytic acid (β=–.27; P=0.02), genistein (β=–.25; P=0.01), and daidzein (β=–.24; P=0.01), and positively associated with percent energy from fatty acids (β=.32; P=0.0006).ConclusionsCompared with EA and NA, OA had a higher dietary intake of fiber, vegetable protein, and phytic acid, which were inversely associated with lumbar spine BMD z scores. Further studies are needed to assess dietary recommendations for OA to optimize bone accrual.