Objective   To observe the effect of soybean protein on the concentration of serum cholesterol in human and to explore the possible mechanism.

  Methods   Fifteen male and 15 female young health college students were divided into 3 groups based on the concentration of serum cholesterol, sex and body weight.Except the same basic diet for each meal, subjects ingested 30g casein or 30g soybean protein or 30g casein with 880mg calcium each day for 14 days, respectively.The body height and body weight were measured at the beginning and the end of the experiment.Blood samples were collected on the day beore and after the trial, and serum total cholesterol was examined.Feces samples were collected totally at the last 3 days of the experiment and the excretion of fecal lipids, calcium, phosphorus, magnesium, and bile acids were measured.

  Results   (1) Compared with the beginning, the concentrat ion of serum total cholesterol from casein group increased significantly at the end of the experiment.Whereas, the increase of serum total cholesterol from solybean protein group and casein with calcium group was insignificant.(2)Compared with casein group, excretions of fecal calcium, phosphorus and magnesium in soybean protein group were increased significantly, excretions of fecal lipids and bile acids were increased by 33.6% and 45.3%, respectively.(3)The fecal bile acid excretion correlated positively with the excretion of fecal calcium, phosphorus, magnesium and lipids.The concentration of serum total cholesterol trended to decrease as the excretion of fecal bile acid increased.

  Conclusion   More excretion of fecal bile acid by intake of soybean protein may induced a low cancentration of serum total cholesterol via increase in the synthesis of bile acids from cholesterol in liver.