The initials FOS represent fructo-oligosaccharides. It is a type of prebiotic of dietary fibers that are formed by polysaccharides and have a positive effect on the intestinal flora. FOS are oligosaccharides of vegetable origin, obtained mainly from bulbous plants such as chicory, leeks and onions. FOS pass undigested into the large intestine and feed the good intestinal bacteria (probiotics). Because breast milk contains only lactose and not fructose, the galacto-oligosaccharide (GOS) prebiotics from lactose are closer to the prebiotic dietary fibres in breast milk than the fructo-oligosaccharides (FOS). This is why HiPP formulas only contain GOS.