Who hasn’t heard about probiotics? But it is to the credit of a Russian scientist Elie Metchnikoff of the Pasteur Institute, Paris who in 1907 observed that villagers living in the Caucasus mountains drank a fermented yogurt drink which he attributed to the longevity of their lives. The bacteria responsible for the fermentation was isolated and found to be Lactobacillus bulgaricus.
Since then, many bacterial and yeast cultures have been isolated from fermented foods, mainly dairy products and vegetables, and individual studies have shown that their consumption have health benefits. Breast milk has been another source of these bacteria. But more recently, the human gut has been found to be the source of these bacteria.
The bacteria so far studied belong to different species and strains of Lactobacillus, Bifidobacterium, Clostridium and Bacillus to name a few. Many of these have been commercialised and presented to the consumer as a fermented product or as a supplement.
The market
The health claims of these bacteria in the form of publications are many. They improve nutrition, exert antagonistic effect on gastrointestinal pathogens, strengthen immunity, have a protective effect against cancer development by binding of mutagens, help relieve constipation, treat ulcerative colitis, irritable bowel syndrome, lower blood pressure, lower cholesterol, help in weight loss and even protect against periodontal disease. Most successful use of probiotics is in treating Clostridium difficile infection, where healthy gut microbiota is altered due to use of antibiotics.
It must be emphasised that most of these publications are case reports, uncontrolled studies or studies of animal, or in vitro studies. Everybody has a different gut microbiota (microorganisms in the gut) which in healthy individuals is in perfect harmony with the human gut.
Probiotic bacteria are outsiders whose survival and proliferation to offer health benefits can happen only when there is impairment of the gut microbiota due to intake of antibiotics. However, there is ‘no-one-size-fits-all’ theory in the benefits of their consumption. It is increasingly being realised that the benefits of probiotics have been overemphasised.
The Food and Agriculture Organization’s definition of probiotic is “Live microorganisms that, when administered in adequate amounts, confer a health benefit on the host.” Besides, for a microbial culture to be truly probiotic, it must be able to withstand the high acidity of the stomach and bile produced by the body, else it will get digested like any other food material. All products in the market do not conform to these requirements and are not permitted to carry the label ‘Probiotic’ by Food Drug Administration, US or the European Food Safety Authority.
New kids on the block
Recently, a study published in Cell found that these probiotics may have a negative effect. A probiotic supplement of 11 strains including Lactobacillus and Bifidobacterium taken after a course of antibiotics, actually delayed the restoration of normal bacteria in the gut for more than five months, while autologous (i.e., obtained from the same individual) fecal microbiota transplant, gathered prior to antibiotic treatment, restored the gut microbiota in a few days.
Despite the pessimism regarding the beneficial effects of probiotics, the search for new bacteria has continued. With new advances in DNA sequencing technology, it has become possible to identify the gut microbiota without the tedious method of isolating and culturing them in the laboratory.
Two bacteria so discovered include, Akkermansia muciniphila and Faecalibacterium prausnitzii (out of 2,172 different species identified in our gut). They form 2-5% of the population of the microbiota and are recognised as bacteria associated with good health. These bacteria were never cultured earlier as they are anaerobic and extremely sensitive to oxygen and hence difficult to study.
It was observed that the number of A. muciniphila was low in obese individuals, type 2-diabetics, hypertension, hypercholesterolaemia and liver disease. So by housing this bacteria in our gut one can protect oneself from these metabolic disorders.
The number of F. prausnitzii was also found to be low in patients suffering from inflammatory bowel syndromes-irritable bowel syndromes, colorectal cancer, obesity and celiac disease. This bacterium is an abundant butyrate producer and hence is suspected to have immune modulatory properties.
Fermented dairy products
Fermented dairy products, besides their delicious taste, need to be appreciated more for their nutritional quality, as they are a good source of proteins, calcium and some B group vitamins. The probiotic properties may be true of only particular strains of bacteria.
Curd is a part of the meal consumed by almost every Indian. Various species of the genus Lactobacillus such as L. fermentum, L. acidophilus, L. confusus, L. delbrueckii, L. lindneri, L. helveticus and Leuconostoc lactis have been found in home-made curd. Lactobacillus delbrueckii sbsp bulgaricus and Streptococcus thermophilus make up the starter culture of the commercially produced curd or yogurt in the country.
There are varying reports on the beneficial effects of these two organisms — while some strains have been found to have health benefits, some don’t. Fermented milk products of other countries have also flooded the market advertising their probiotic properties.
Further, probiotics can be obtained not only from fermented dairy products but also from fermented foods prepared from cereals and vegetables.