High Vegetable Protein Diet is Associated with Low Lumbar Spine Bone Mineral Density in Amenorrheic Athletes

Abstract

PURPOSE: We have reported that amenorrheic athletes (AA) have a higher intake of dietary fiber compared to eumenorrheic athletes (EA) and non-athletes (NA), which is negatively associated with lumbar BMD. High fiber diets are rich in vegetable proteins, and food rich in vegetable protein has high concentrations of phytic acid and isoflavones, and low concentrations of saturated fatty acids (SFA). Fiber and isoflavones are reported to have negative associations with serum estrogen. We hypothesized that a diet high in vegetable protein may contribute to low BMD in AA. METHODS: 4-day food records and serum samples were collected from 68 AA, 24 EA, and 26 NA 14–23 yo. Energy availability was calculated as (energy intake- energy expenditure)/ fat free mass. DXA was used to assess lumbar spine BMD. RESULTS: EA were younger than AA and NA (p=.04), and AA had lower BMI (p=.04). Exercise activity did not differ in AA and EA. There was no difference in energy availability among groups. Compared with EA and NA, AA had higher intake of fiber (AA=34.8±15.3; EA=22.5±11.7; NA=17.2±6.6g; p<.0001), phytic acid (AA=1276±621; EA=621±384; NA=700±370mg; p<.0001), and vegetable protein (AA=45.6±19.2; EA=31.9±12.9; NA=26.8±8.8g; p<.0001). Intake of isoflavones was higher in AA than NA (genistein: AA=7.4±10.1; EA=2.7±6.7; NA=1.4±4.2g; p=.003; daidzein: AA=5.9±8.0; EA=2.0±4.8; NA=1.0±2.9g; p=.0002). AA had a lower intake of % calories from SFA than NA (AA=8.6±2.6; EA=9.8±2.2; NA=10.6±2.6; p=.002). After controlling for menstrual status, calcium intake and serum vitamin D, spine Z-scores were associated inversely with vegetable protein (SE=−.34, p=.006), phytic acid (SE=−.32, p=.005), genistein (SE=−.29, p=.003), and daidzein (SE=−.28, p=.005) ; and positively with %SFA after also controlling for fiber (SE=.26,p=.02). CONCLUSIONS: We found a higher vegetable protein diet in AA than EA and C, associated inversely with spine Z-scores. Because phytic acid and dietary fiber decrease energy and mineral absorption, some AA may have adequate energy intake but be nutrient deficient. Furthermore, the ability of dietary fiber and isoflavones to decrease estrogen may affect BMD. Studies examining nutrients affecting bone metabolism and estrogen levels in female athletes are needed to develop optimal dietary recommendations.