The human gut microbiota is involved in a cascade of activities essential for body health. Their imbalance can lead to significant metabolic abnormalities and a plethora of diseases. Prebiotics have emerged as an effective nonpharmacological approach to re-establish gut symbiosis and promote well being.
Prebiotics are basically nondigestible fiber compounds in foods, and are composed of oligosaccharides. They stimulate the growth of normal gastrointestinal flora, which in turn hinders the growth of abnormal flora and pathogens. Common examples of prebiotics include fructo-oligosaccharides (FOS), inulin, arabinogalactan, polydextrose, lactulose and lactitol.
Variety of prebiotic foods, raw green banana, asparagus, onions, garlic, leeks, berries and green beans. Image Credit: SewCream / Shutterstock
Prebiotics resist hydrolytic activity in the upper part of the gastrointestinal tract and thus reach the colon in an intact form. Here they are subjected to selective fermentation by beneficial microflora, which ultimately changes the composition of the colonic microbiota. Prebiotics generally stimulate the growth of bifidobacteria and lactobacillus, which confers several beneficial effects on the host like improving digestion and strengthening the immune system.
The health benefits of prebiotics are mainly attributed to the increased production of short-chain fatty acids (SCFA). SCFA are the chief end-products of prebiotic fermentation, and they play an important role in modulating the intestinal barrier. SCFA are also involved in regulating the immune system and inflammatory response.
Prebiotics are not only modulators of gut microbiota, but their potential is being harnessed in a number of diseases such as colorectal cancer and inflammatory bowel diseases. They also aid in the absorption of several minerals, and help in the prevention of obesity and relieving constipation.
Effects on the Immune System
One of the beneficial effects of prebiotics is the stimulation of the immune system. Gut microorganisms are known to impact multiple aspects of the innate and adaptive mucosal immune system. The effects can be direct, or indirect by increasing the population of beneficial microbes or probiotics, especially of lactic acid bacteria and bifidobacteria. Prebiotics stimulate the activity of gut-associated lymphoid tissues (GALT) which confers a state of well-being and reduces the risk of diseases.
Colorectal Cancer Prevention
Prebiotics may be beneficial in the prevention of colorectal cancer by modifying the composition or activity of the colorectal microflora. The production of SCFA and modifications of gene expression in cancerous cells are the major mechanisms thought to be responsible for the anticancer effects. Many epidemiologic and preclinical studies have also demonstrated a reduction in the levels of various biomarkers of colorectal cancer after the administration of prebiotics.
Prevention of Inflammatory Bowel Disease
Dysbiotic intestinal microbiota is the major cause of inflammatory bowel disease and hence there has been pioneering research in developing new treatments which target the gut microflora. Prebiotics improve the gut mucosal barrier and modulate the microflora, and hence help in the prevention of Inflammatory Bowel Disease (IBD). It has been postulated that prebiotics nourish the bowel wall, through the production of SCFAs, and are thus beneficial in Crohn's disease. In ulcerative colitis, prebiotics are assumed to decrease the production of hydrogen sulfide gas due to a reduction in the number of sulfate-producing bacteria. These sulfate-producing bacteria are unable to thrive in the slightly acidic environment created by SCFAs.
Intestinal dysbiosis is a major cause of constipation. By stimulating the growth of beneficial bacteria, prebiotics like bifidobacteria act as a viable option in relieving constipation. SCFA production by these bacteria play a pivotal role in modulation of intestinal motility by exerting a trophic effect on the epithelial cells. This ultimately leads to increased blood flow in the region and increased intestinal motility.
Prevention of Obesity
Gut microbiota is involved in the development of low-grade inflammation which disrupts the metabolism of glucose and the absorption of fats. These disruptions are distinctive features of obesity. Prebiotics improve the gut barrier integrity and reduce intestinal low-grade inflammation, thus ameliorating metabolic alterations and promoting weight loss. Studies have linked prebiotics with an increased secretion of satiety promoting peptides - glucagon-like peptide-1 (GLP-1) and peptide YY (PYY) and a decreased production of ghrelin, a peptide which promotes appetite and adiposity. These combined effects of prebiotics may have therapeutic potential for obesity.
The cholesterol-lowering effects of prebiotics are mainly due to the production of SCFAs by prebiotics. The SCFAs generated are absorbed in the portal vein and metabolized by the liver, resulting in the lowering of blood pressure. Prebiotics are also involved in the absorption of fats and phospholipids in the lower intestine. This binding effect of prebiotics also leads to decreased levels of cholesterol. A decreased level of total cholesterol increases the clearance of LDL cholesterol and potentially reduces blood pressure.
Improve the Absorption of Several Minerals
Prebiotics improve the absorption of vital minerals such as calcium and magnesium, which in turn has beneficial effects on bone mineralization. The SCFA produced by prebiotics help in acidification of the gut lumen, which increases the solubility of the minerals in the gut and leads to increased expression of calcium-binding proteins in the large intestine.
The influence of nutrition on human health is well known; however, there is still ignorance about some of the important dietary components that are helpful for human metabolism. Prebiotics are necessary additives to diet and can have a positive influence on human health. Numerous diseases are also associated with gut microbiota imbalance, and prebiotics seems to represent an effective nonpharmacological approach to treat them.