Experimental colorectal cancer: the relationship of diet and faecal bile acid concentration to tumour induction.

Epidemiological studies have consistently suggested an aetiological relationship between certain dietary constituents, faecal bile acid (FBA) concentration and colorectal cancer. This study was designed to examine the effect of the dietary manipulation of fat and fibre on tumour induction and on various faecal characteristics in Albino Swiss rats. A total of 232 animals were maintained on one of four different diets for 4, 20 and 28 weeks respectively. The diets were classified as high fat high fibre, low fat high fibre, high fat low fibre and low fat low fibre. The groups were further sub-divided according to the administration of systemic azoxymethane (10 mg/kg per week) or saline over 12 consecutive weeks. The high fat low fibre diet was associated with the highest risk for tumour production and the low fat high fibre diet with the lowest risk. Statistically significant differences between all the diets were noted with the exception of a comparison between the high fat high fibre and low fat high fibre diets. The highest total concentration of free FBA was found in the faeces from animals fed low fibre containing diets. The results show a clear influence of both fat and fibre on tumour induction while, in this model, fibre was the principle determinant of faecal bile acid concentration.