Whitehead ratio was investigated as an indicator of protein nutrition, observing the effect of low protein diet. Twelve male adults were divided into 3 group. The first group was given low protein diet and allowed to live quiet daily life. The second group was given more 1000Cal in the period of low protein diet living quiet daily life as well, and the third was treated to do hard work of R.M.R. 8 for two hours daily in the period of standard and low protein diet. The result was as follows. 1) In the period of low protein diet, gradual decline of the function in adrenal and basal metabolism was observed gradual decrease in hemoglobin and serum protein concentration was remarkable in each group. On the second group the anemia and the decrease of basal metabolism were less remarkable than the first group, but it was uncertain that this depended upon the diminished intake of protein. Although all subjects of the third group were sportsmen proficient in exercise, they showed the symptom of anemia, decrease of serum protein, and decline of function in other physiological organs. 2) On each group Whitehead ratio increased in the period of low protein diet. The increase of Whitehead ratio was considered to indicate, in some degree, the protein deficiency, but the rang of difference was very small. 3) The increase of N/E ratio in the period of low protein diet is mainly caused by the decrease of essential amino acids and also by increase of nonessential amino acids. This is considered to depend on the degree of protein deficiency. 4) The correlation between Whitehead ratio and N/E ratio is considerably high. Therefore Whitehead ratio can be used as an indicator of protein nutrition decision, if normal range of Whitehead ratio is applied in many cases under the standard protein level.