Effect of Soymilk and Exercise on Bone Mineral Density and Bone Metabolism Related Markers in Underweight College Women with Low Bone Density

The objective of this study was to investigate the effect of soymilk and exercise on bone mineral density (BMD) in underweight college women of 19-22 years of age, who had lower bone mass. The BMD of the lumbar spine and femoral neck was measured for 52 underweight college women. Among them, 33 subjects, whose t-score value was below -1, were selected. Questionnaire survey, anthropometrical measurements, dietary recall, analysis of BMD, fasting serum osteocalcin and urinary deoxypyridinoline (DPD) were conducted before and after the 10 week study. The 33 subjects were divided into 2 groups： soymilk group (n=19), and soymilk ＋ exercise group (n=14). The soymilk group was given 400$m\ell$ soymilk containing 60mg of isoflavones on a daily basis and the soymilk ＋ exercise group exercised three times a week with a daily intake of 400$m\ell$ soymilk for 10 weeks. The average ages of the soymilk group and the soymilk ＋ exercise group were 21.1 years and 20.4 years, respectively and, there were no significant differences between the soymilk group and the soymilk ＋ exercise group in the areas of height, weight or Body Mass Index (BMI). At the baseline, the mean daily energy intake of the soymilk group and the soymilk ＋ exercise group was 1,597.9kcal (79.43％ of RDA) and 1,704.2kcal (85.2％ of RDA), respectively. The mean calcium intake of the soymilk group (408.3mg) was not significantly different from that of the soymilk ＋ exercise group (389.4mg). Despite the 400$m\ell$ soymilk supplementation, there were no significant changes of nutrient intake in either group after treatment. However, there were significant increases in BMD's of lumbar spine and femoral neck in both groups. There were some increases in the serum osteocalcin level and decreases in the urinary deoxypyridinoline level as well. BMD change of the soymilk group was not significantly different from that of the soymilk ＋ exercise group. In conclusion, supplementary intake of soymilk (containing 60mg of isoflavones) resulted in a significant increase in the BMD's of the lumbar spine and femoral neck in underweight college women with low bone mass. However, exercise did not result in any significant changes in the BMD's, implying the necessity for more intensive and specific long-term physical training for any substantial changes. Further investigation is necessary to determine the exercise that most strongly affects BMD.