Beneficial effects of rice endosperm protein intake in Japanese men with risk factors for metabolic syndrome: a randomized, crossover clinical trial

BACKGROUND: Rice protein is proved to have hypocholesterolemic and anti-atherosclerotic effects, and a few experimental studies showed its renoprotective effects, using animal diabetic models. However, no clinical studies have investigated its benefits for human health. We aimed to clarify how the intake of rice endosperm protein affects markers correlating to lipid dysfunction in human. METHODS: We recruited 18 male volunteers, 26–64 years of age, with risk factors for metabolic syndrome and allocated randomly into two groups. Half of them were administered test food containing rice endosperm protein and other half were administered control food containing sodium caseinate for 4 weeks. The dose of supplemental protein was 10 g/day. After medical examinations, the study foods were switched and the intervention was continued for another 4 weeks. Lipid metabolism markers were evaluated as primary outcome measures. Cross-over analysis was performed for 18 subjects using physical and clinical values measured before and after each intervention period. RESULTS: The serum high-density lipoprotein cholesterol (HDL-C) level was increased at 0.08 mmol/L [interquartile range (IQR) from −0.05 to 0.19 mmol/L] during the period when rice endosperm protein was administered (the rice endosperm protein period), whereas it was decreased at −0.04 mmol/L [IQR from −0.13 to 0.05 mmol/L] during the period when casein was administered (the casein period). Treatment effect was significant with P = 0.047. Changes in total cholesterol, low-density lipoprotein cholesterol and triglycerides were not different between treatments. Among the secondary outcome measures, decrease in serum uric acid (UA) during the rice endosperm protein period [−24 μmol/L (IQR from −39 to −6 μmol/L)] was greater than that during the casein period [0 (IQR from −6 to 13 μmol/L)] with a significant treatment effect (P = 0.030). CONCLUSION: Supplemental intake of rice endosperm protein may elevate serum HDL-C level and lower serum UA level in male subjects with ...