Long-term effect of shoyu (Japanese soy sauce) on the gastric mucosa of the rat.

The long-term effect of shoyu (Japanese soy sauce) on the gastric mucosa was assessed in intact rats and in those with a fundusectomy. One hundred female 4-month-old Wistar rats were divided into 4 groups:intact and operated rats on a control diet and intact and operated rats on the same diet saturated with shoyu. The animals given shoyu were smaller than the controls; 15 intact rats receiving the sauce were healthy at 33 months compared with 7 controls. Only 9 of 50 operated rats lived 33 months. Breast tumors developed in 10 control rats but in none given shoyu. The distribution of other tumors was the same. Two malignant neoplasms appeared to originate in the perigastric tissues of operated rats: a reticulum cell sarcoma in the shoyu group and a lymphosarcoma in the control group. None involved the gastric mucosa. Most of the operated rats (with or without shoyu) developed small benign gastric tumors. Mucosal histology was well preserved in 22 intact rats on shoyu: In 15 it was normal, in 7 there was mucus loss and nuclear changes in the cells of the gastric pits; 2 of the 7 had mild gastritis. One intact control showed patchy mucus loss. Shoyu did not appear to be a carcinogen in the rat; its prolonged use impaired neither health nor longevity. Long-term use was associated with gastric mucus loss and nuclear changes in a few rats, occasionally with a mild gastritis.