Abstract
The effects of ingested protein level on urinary creatinine excretion were exami ned in adult male subjects in a long-term test period. Results obtained were as follows:
1) Two human male subjects received the basal diet containing 2400 Cal. and 80g. of protein daily for 20 days, and then the protein level was reduced to 20g. for 16days, successively 40g. for 40 days or more. According to the ptotein deficit, urina-ry creatinine levels were significantly lowered by 7 to 12% in 20g. protein level and by 13 to 17% in 40g. protein level, compared with the value of the basal diet. The creatinine coefficient was also decreased. These findings were confirmed by rats, when the protein level was lowered to 5%.
2) In the case of high protein administration or qualitative variations of ingested protein, there were no changes on creatinine excretion in human adult subjects. In adult rats, creatinine level was slightly elevated when the dietary protein level was increased from 15 to 25%, but this increments were statistically insignificant.
3) As the free and phosphate creatine of rat muscle were found fairly constant independent of the quantity of the protein intake, the lowered level of creatinine excretion by protein restriction may not be attributed to spontaneous conversion of muscle crea-tine fraction to urinary creatinine as suggested by Borsook et al.
