Effect of Metamucil on tumour formation by 1,2-dimethylhydrazine dihydrochloride in mice.

The effect of the plant cellulose metamucil on the tumorigenicity of 1,2-dimethylhydrazine dihydrochloride (1,2-DMH) was studied in random-bred Swiss mice. Three groups of mice, which were 5, 6 and 6 weeks old at the beginning of the experiment, were given the following treatments: (1) metamucil (20%, w/w) in powdered diet for their lifespan; (2) 1,2-DMH, ten weekly subcutaneous injections at 20 mg/kg body weight; (3) combination of treatments given to groups 1 and 2. The administration of metamucil enhanced the appearance of colon tumours induced by 1,2-DMH in males only. Metamucil had no statistically significant effect on the development of tumours elicited by 1,2-DMH at seven additional sites. It was expected that a high amount of dietary fibre would inhibit carcinogenesis in the large intestine. Instead, metamucil increased the incidence of colon tumours induced by 1,2-DMH, although only in males.