Diet, butyric acid and differentiation of gastrointestinal tract tumours.

Butyric acid has two contrasting functional roles. As a product of fermentation within the human colon, it serves as the most important energy source for normal colorectal epithelium. It also promotes the differentiation of cultured malignant cells. A switch from aerobic to anaerobic metabolism accompanies neoplastic transformation in the colorectum. The separate functional roles for n-butyrate may reflect the different metabolic activities of normal and neoplastic tissues. Relatively low intracolonic levels of n-butyrate are associated with a low fibre diet. Deficiency of n-butyrate, coupled to the increased energy requirements of neoplastic tissues, may promote the switch to anaerobic metabolism. The presence of naturally occurring differentiating agents, such as n-butyrate, may modify the patterns of growth and differentiation of gastrointestinal tumours.