Reported functional disturbances include increased intestinal permeability, deficient enzymatic activity of disaccharidases, increased secretin-induced pancreatico-biliary secretion, and abnormal fecal Clostridia taxa. Some children placed on exclusion diets or treated with the antibiotic vancomycin are reported to improve in cognitive and social function. Furthermore, a recent study found a strong correlation between GI symptoms and autism severity. The intestinal mucoepithelial layer must maximize nutritional uptake of dietary components while maintaining a barrier to toxins and infectious agents. Although some aspects of these functions are host-encoded, others are acquired through symbiotic relationships with microbial flora. Dietary carbohydrates enter the intestine as monosaccharides, disaccharides, or complex polysaccharides. Following digestion with salivary and pancreatic amylases, carbohydrates are further digested by disaccharidases expressed by absorptive enterocytes in the brush border of the small intestine and transported as monosaccharides across the intestinal epithelium. Although humans lack the glycoside hydrolases and polysaccharide lyases necessary for cleavage of glycosidic linkages present in plant cell wall polysaccharides, oligosaccharides, storage polysaccharides, and resistant starches, intestinal bacteria encoding these enzymes expand our capacity to extract energy from dietary polysaccharides. As an end product of polysaccharide fermentation, bacteria produce short-chain fatty acids that serve as energy substrates for colonocytes, modulate colonicpH, regulate colonic cell proliferation and differentiation, and contribute to hepatic Calceolarioside-B gluconeogenesis and cholesterol synthesis. Intestinal microbes also mediate postnatal development of the gut mucoepithelial layer, Gelsemine provide resistance to potential pathogens, regulate development of intraepithelial lymphocytes and Peyer��s patches, influence cytokine production and serum immunoglobulin levels, promote systemic lymphoid organogenesis, and influence brain development and behavior.