BACKGROUND: Many data demonstrate that the components of soybean can lower blood lipid,suppress the growth of cancer cells and exert weak estrogenic activities. However,little is known about the effect of isolated soybean protein on the lifespan of the organism.OBJECTIVE: To observe the effect of isolated soybean protein on the lifespan of drosophila melanogasters and investigate the mechanism of effective anti-aging and anti-oxidation action.DESIGN: A controlled trial based on drosophila melanogasters.SETTING: Department of nutrition and food hygiene in a university.MATERIALS: The experiment was conducted in the Department of Nutrition and Food Hygiene,Public Health College of Xinjiang Medical University from March to June 2002. A total of 400 drosophila melanogasters of American wild type with half for each gender were provided by the Department of Nutrition and Food Hygiene, Public Health College of Xinjiang Medical University.METHODS: The 400 drosophila melanogasters were divided into control group(normal culture) and three-dosage experiment groups(normal culture contained isolated soybean protein 0.2%,1.0% and 5.0%,respectively).From the second day on, the number of living and dead drosophila melanogasters was observed and counted until all died. Meanwhile, mean lifespan,half death time and maximal lifespan were calculated.MAIN OUTCOME MEASURFS: Mean lifespan, half death time and maximal lifespan of the drosophila melanogasters.RESULTS: Compared with that of control group, the lifespan of male and female drosophila melanogasters in experiment groups was prolonged by isolated soybean protein and responded in a dose-dependent manner,especially in high-dosage group. The mean lifespan, half death time and maximal lifespan of both female and male drosophila melanogasters were prolonged by 24.5% and20.7%,27.1% and22.0%,and 13.9% and 10.6%,respectively.CONCLUSION: Isolated soybean protein may have anti-aging and lifespan-prolonging effects on drosophila melanogasters.