What Does Prebiotics XOS+GOS Do? Beneficial bacteria can be depleted by low-fiber diets, high meat diets, antibiotic use, travel and stress. Jarrow Formulas' Prebiotics XOS+GOS primarily supports the growth of Bifidobacteria but also Lactobacilli for intestinal and immune function. PreticX (Xylooligosaccharides) has been shown in clinical studies to promote the growth of Bifidobacteria. GOS (Galactooligosaccharides) are the principal type of prebiotics found in human milk.