Fructooligosaccharides (FOS) are naturally occurring functional oligosaccharides, which are composed of 2 to 10 fructose molecules combined with glucose molecules. They are widely found in natural plants such as bananas, onions, garlic, chicory, and honey. As a typical prebiotic, fructooligosaccharides cannot be digested and absorbed by the human body, but are selectively fermented by beneficial gut bacteria, especially bifidobacteria, to promote gut health, support microbial balance.