Figure 1. Metabolic cross feeding during gut colonization.

Fructooligosaccharides (FOS) reach the colon largely intact where they serve as substrates for fructan-degrading bacteria such as Bifidobacteria. Utilization of down-stream products by other bacterial species, termed metabolic cross-feeding, results in production of short-chain fatty acids that are absorbed by the host. Strain variation in FOS-degradative capacity results in diet-dependent colonization or replicative capacity.