Mild ingestion of used frying oil damages hepatic and renal cells in Wistar rats.

Male Wistar rats were fed ad libitum a powdered diet (AIN93G; no fat) containing 7 wt% of fresh oil (control) or used frying oil recovered from Japanese food manufacturing companies (recovered oil) for 12 weeks and subjected to anthropometric measurements, hematological analyses, and observations of the liver and kidneys. All of the rats grew well, and no gross symptoms attributable to recovered oil were observed. There was a tendency toward higher consumption of the diet in the experimental group as compared to the control group. In the serum of the experimental group, no difference was detected in the levels of glucose, triacylglycerol, and phospholipids. But many dark-red patches, necrosis, and bleeding were found in the livers of 75% of the experimental rats; these rats had extremely high aspartate aminotransferase (AST) and alanine aminotransferase (ALT) values. Average AST and ALT values of the experimental group were significantly higher than those of the controls. The renal cells were also obviously damaged. These results raise the concern that frying oil contained in ready-made foods, snacks, etc., if deteriorated to an extent equal to or greater than that of the recovered oil, may be able to change human serum AST/ALT levels and damage the liver and kidneys.