The proportion of dietary protein modifies the tumorgenesis of glandular stomach in rats that received NG in drinking water. If a 50% casein diet is given regularly from the date of carcinogenic stimulus by NG, the final tumor number and their malignancy are more pronounced than in other groups maintained on 20% or 36% casein diets.36% casein diets, when given concurrently with the carcinogen throughout the experimental period, showed slightly more accelerated tumorgenesis than rats on 20% casein diets, but there were about the same number of malignancies. The survival time of rats on 5 % casein diets was too short and no tumors developed among rats that survived 5 to 6 monthes after experimental initiation. The general conclusion drawn from these data is that high dietary protein exerts a potentiation effect on NG tumorgenesis, especially in carcinogenesis.
In our preliminary report, the genesis and development of NG-induced gastric tumor in rats maintained on a 50 percent casein diet throughout the experiment were enhanced more significantly than those fed on a low protein diet. An attempt was made to determine at what phase of the neoplastic process casein might be considered to have its effect. Alterations in the dietary protein content were performed on the 20th week after the initiation of the experiment. This caused a slight increase in the genesis and tumor growth of the glandular stomach by giving a higher protein diet but did not show a significant difference. Urine volume and urea nitrogen excretion of rats fed on 50 percent casein diet manifested a significant increment compared with those of rats fed on 20 and 8 percent casein diets. Thus, the uptake of a high protein diet appears to influence the metabolism of rats receiving NG, but the details remain to be elucidated.