Introduction: Transmethylation modifies configuration and proceeds via formaldehyde. It has a significant role for example in epigenetic regulation. The whole methyl-pool can be evaluated by the measurement of bound formaldehyde. Aim: The bound formaldehyde was measured in wheat, bean, beetroot, cabbage, broiler- and rabbit liver. The relationship between transmethylation and redox homeosthasis was studied in the liver of domestic animals, and in the rat model of fatty liver. Method: The diet of rats was enriched with cholesterol, sunflower oil and cholic acid. The bound formaldehyde was determined by overpressured layer chromatography. The hydrogen-donating ability was measured with 1.1-diphenyl-2-picrylhydrazylt free radical using spectrophotometric measurement. Results: Beans had the most bound formaldehyde. The liver of broilers possessed significantly elevated hydrogen-donating ability and transmethylation ability. Rats with severe fatty liver had significantly less bound formaldehyde and the hydrogen-donating ability tendentiously decreased. Conclusions: These results draw attention to the diet, especially in obesity and obesity-related diseases. Orv. Hetil., 2013, 154, 1180–1187.