Source Naturals FOS POWDER Dietary Supplement, Fructooligosaccharides Probiotic Enhancer - 100 GramsSOURCE NATURALS FOS BENEFITS. This supplement is a complex of fructooligosaccharides, a group of naturally occurring carbohydrates that can help promote the growth of beneficial flora in the gastrointestinal tract.SUGGESTED USE. 1 rounded teaspoon daily, mixed in water or juice as desired.SUITABLE F..