The gastrointestinal (GI) tract can significantly harbour an extensive range of bacterial species. Some of these bacteria are beneficial. They are able to protect the host against the invading bacteria and viruses and facilitate digestion. Probiotic bacteria are characterised as health promoting microorganisms that are able to generate inhibitory substances against harmful bacteria in the body. These substances consist of organic acid, hydrogen peroxide and bacteriocins which can decrease the metabolism of destructive bacteria and the toxin yields.
Compared to the conventional animals, the germ free animals are usually more sensitive to the infection. This is mainly attributed to the low immune system and the lack of competitive colonization. Research demonstrated that the microbial colonization can provide some essential health benefits for human body.
Microbes however, are likely to develop the pathogenic interactions with a host that can result in occurring diseases or even death of the host. Microbial metabolites can exert mutagenic or carcinogenic activity. As a result cancer can develop during the long period of the exposure. The activities of the commensal microbes can be inhibited by the presence of probiotics in the body.
Yoghurt as an effective probiotic food contributes to numerous health functions in the body. Regular consumption of yoghurt helps higher absorption of B-vitamins and calcium. People with lactose intolerance are not capable to digest and absorb lactose in the body, i.e. they are allergic to lactose-based milk. The metabolised lactose can cause abdominal pain, bloating, diarrhoea and nausea. The ingestion of yoghurt helps improve the lactose digestion in the body. The active cultures of yoghurt which include Streptococcus thermophilus and lactobacillus delbrueckii subsp. Bulgaricus are able to produce lactase enzymes. The lactose-intolerant individuals lack this enzyme and therefore regular intake of yoghurt helps easier digestion of the milk protein (casein). The culturing process also enables the activity of beta-galactosidase enzyme (develops in some types of yoghurts). This enzyme is significantly contributory to lactose absorption in the body of people with lactase deficiency.
Invivo studies described that probiotic bacteria exhibit health benefits on reducing the concentration of blood cholesterol. The mechanism is based on reducing the absorption of serum cholesterol in the intestine, involving cholesterol in the cellular membrane and converting cholesterol into coprostanol. It has been reported that the reduction of serum cholesterol is potentially in response to the ability of lactic acid bacteria (the genera lactobacillus and bifidobacteria) to deconjugate bile acids (enzymatically) and help increase their excretion from the body.
Probiotics are also protective against Helicobacter pylori infections in the stomach, over-population of bacteria in small intestine, colon cancer, ulcerative colitis, Juvenile chronic arthritis, asthma, hepatic encephalopathy and gastrointestinal disorders.
Prebiotics are known as non-digestible food components that increase the growth and health effects of beneficial bacteria in the gastrointestinal tract. They may be added to the dietary foods to enable the effective bacteria to grow and survive in the digestive mechanism. The health properties of prebiotics include anti-carcinogenic, antimicrobial, anti-inflammatory, hypolipidemic and glucose-modulatory. Frequent consumption of prebiotics improves the absorption of minerals and provides anti-osteporotic effects. Anti-carcinogenic action of prebiotics is not specifically clear. It is probably due to the potential action of butyrate. Butyrate is created by bacterial fermentation of different prebiotic oligosaccharides in the colon.
Many reports have shown that prebiotic oligosaccharides contribute to the increment of calcium and magnesium concentration in the colon. The increased concentrations of these cations in the colon aids controlling the extent of cell turnover. For instance, the presence of calcium in the colon helps control the formation of insoluble bile or salts of fatty acids. Hence, the potential impact of bile or fatty acids on the colonocytes is curtailed.
In vitro studies have stated that some friendly bacteria including the genera bifidobacteria and lactobacilli
are able to yield antimicrobial substances, develop antigen specific/non-specific immune responses and inactivate some carcinogens. They can inhibit the growth of tumors and suppress the growth of bacteria which are likely to convert precarcinogens into carcinogens. The growth of these beneficial bacteria is stimulated by the present prebiotics in large intestine.
Sufficient intake of prebiotic foods considerably maintains the health and protects the body against some intestinal pathogens, inflammatory bowel disease and some carcinogenic impacts. Excessive ingestion of prebiotic oligosaccharides can lead to adverse reactions such as gastrointestinal symptoms such as flatulence, bloating and diarrhoea.