The investigators have conducted a study about the effects of normal diet (phosphorus 1500mg) and low-phosphorus diet (phosphorus 500mg) on phosphorus homeostasis in healthy men. The results showed low-phosphorus diet could significantly reduce serum phosphorus and urine phosphorus level compared to normal diet. However, the levels of serum FGF23 and a-klotho were not different between these two groups.Thus, the investigators want to further explore the effects of high-phosphorus diet (phosphorus 2300mg)on phosphorus homeostasis in healthy men.