Volatile fatty acids: their production, absorption, utilization, and roles in human health.

The evidence shows that microbial fermentation of carbohydrates and endogenous substrates occurs in the large intestine of humans and that VFA represent a major endproduct. The large number of bacterial species, the complex nature of their interactions, and the endproducts of their fermentation processes are all likely to have significance in human health. Fermentation in the human intestine resembles rumen fermentation with respect to the metabolic pathways involved in anaerobic degradation of organic matter and in the concentrations of VFA endproducts. Thus, rumen bacteria are useful for understanding the dynamics and potential interactions of human intestinal bacteria. Current research is directed towards examining fermentation processes in animals, such as the pig and some species of monkey, since these animals most closely resemble the human. From such animal studies the metabolic activities of VFA and the processes by which they are produced and absorbed can be more clearly investigated and understood. The effects of diet on the microflora and on the metabolic pathways leading to the generation of VFA are under investigation. Modification of diet seems the most likely way of modifying the extent to which VFA are produced and absorbed by the human. As methodologies and protocols for evaluating human intestinal fermentation in vivo are revised and made more sensitive, the significance of fermentation will become more clearly understood. However, it appears that VFA make a physiologically significant contribution to the health of the colonic mucosa, and to the energy supply of the host. The magnitude of these effects is probably influenced by diet.