 Prebiotic fibers, such as galacto-oligosaccharides GOS, selectively enhance growth of beneficial colonic bacteria. GOS are enzymatically produced from lactose and are a mixture of glucose- and galactose- based di- and oligosaccharides of varying structure and seem to have an increased selectivity towards Bifidobacterium spp compared to other prebiotics. Prebiotics in general enhance the production of short-chain fatty acids SCFAs and thereby decrease luminal pH, which may reduce growth of enteropathogens. Through the reduction in colonic pH, prebiotics can enhance absorption of minerals such as calcium and magnesium and they have been proposed to potentially improve iron absorption, by reducing ferric to ferrous iron in the colon. Even though colonic absorption is minimal compared to absorption in the duodenum in healthy humans, it may become more important in iron deficiency or anemia as demonstrated in animal studies. 