Probiotics: Definition, Strains With Evidence, Curd and the Indian Rules

Probiotics are live microorganisms that, given in adequate amounts, have been shown to benefit the health of the person taking them. That is the FAO/WHO definition, and the Indian rules follow it. The word describes a tested strain at a counted dose, not any fermented food. FSSAI requires a probiotic food to deliver at least 100 million colony-forming units (CFU) in the recommended daily serving and permits 30 named organisms. The best trial evidence is for preventing diarrhoea during a course of antibiotics. This entry belongs to the supplements section of the handbook.

Gut health as a whole, including fibre, prebiotic foods and daily habits, is covered in gut health basics and is not repeated here. The difference between dahi and packaged yoghurt has its own page, curd against yoghurt. What follows is narrower: the definition, the trials, the Indian rules and the cautions.

What is a probiotic, and what is not?

A probiotic has to meet three conditions at once. The organisms must be alive when you take them, the amount must be adequate, and a health benefit must have been demonstrated. A joint FAO/WHO expert consultation set out that wording, a FAO/WHO working group turned it into evaluation guidelines in 2002, and an international expert panel that met in 2013 kept the definition unchanged. FSSAI's regulations define a food with added probiotic ingredients in nearly the same terms: live microorganisms which, taken in adequate numbers as a single strain or a combination, confer specified or demonstrated health benefits.

The second idea to hold on to is that effects belong to strains, not to the whole category. The FAO/WHO working group stated that the evidence points to probiotic effects being strain specific, and the ICMR-DBT guidelines repeat it. A result for one strain of Lactobacillus rhamnosus says nothing certain about another strain, another species or a mixed capsule. The working group named one possible exception: the ordinary yoghurt cultures, Streptococcus thermophilus and Lactobacillus delbrueckii subspecies bulgaricus, appear in general to help people with lactose intolerance digest lactose.

The Indian position: ICMR-DBT guidelines and no ICMR-NIN requirement

India has had its own guidance since 2011, when a task force of the Indian Council of Medical Research and the Department of Biotechnology published the ICMR-DBT guidelines for evaluation of probiotics in food. They adopt the FAO/WHO definition and list what a strain must pass before a food may be called probiotic. They do not cover probiotics sold as drugs or genetically modified organisms. Two points are particular to India: strains in use should be deposited in an internationally recognised culture collection, and a product proven abroad should also be tested for efficacy in Indian subjects.

ICMR-NIN sets no requirement for probiotics. Its 2020 nutrient requirements cover energy, protein, fats, vitamins and minerals, and live bacteria are not nutrients. The Dietary Guidelines for Indians (2024) deal with fermented food as food: a healthy meal is described as including plain fermented yoghurt or curd, the model daily plate carries 300 ml of milk or curd, and fermentation in idli, dosa and dhokla is credited with improving digestibility and the availability of micronutrients. None of that is advice to buy a supplement.

What do FSSAI's rules allow in a probiotic food?

FSSAI allows only organisms listed in Schedule VII of its health supplement and nutraceutical regulations, or approved by the Authority, and each must be declared on the label and be non-GMO. The original schedule named 28 organisms; the 2021 amendment updated the names and added Bacillus clausii and established probiotic strains of Bacillus subtilis, making 30. The live count rule also changed. It first read at least 100 million CFU per gram; from the amendment in force on 6 September 2021 it reads at least 100 million CFU in the recommended serving size per day.

The regulation points readers to the ICMR-DBT guidelines for additional information on use, so the two documents are meant to be read together. One limit of this entry should be stated: the text read here is FSSAI's compendium dated 29 September 2021. Later amendments, if any, were not checked.

Are curd, idli and kanji probiotics?

By the definition and by Indian regulation, not automatically. FSSAI's rule says in terms that the common starter cultures of lactic acid bacteria used to make fermented milk, dahi and related products shall not be considered probiotics if their probiotic properties have not been substantiated. Home-set dahi contains live bacteria, but nobody has identified the strains in your katori, counted them or tested them in a trial. That makes dahi a good food with live cultures. It does not make it a probiotic in the sense a label or a study uses the word.

This is no reason to drop these foods. Dahi supplies protein and calcium, and the milk and dairy tables give the figures; a bowl of curd rice or a plate of steamed idli earns its place in a meal as food. The point is only that a trial result for a named strain cannot be transferred to them.

Which uses of probiotics have trial evidence?

Preventing diarrhoea during antibiotic treatment has the firmest support. A 2019 Cochrane review pooled 33 trials in 6,352 children: diarrhoea occurred in 8 per cent of those given a probiotic with the antibiotic and 19 per cent of controls, so about nine children were treated for one to avoid it. The certainty was rated moderate, and 20 of the 33 trials were at high risk of bias. Trials using 5 billion CFU a day or more showed the larger effect. The reviewers judged it premature to draw conclusions beyond Lactobacillus rhamnosus and Saccharomyces boulardii.

A 2017 Cochrane review looked at the more serious diarrhoea caused by Clostridium difficile in adults and children on antibiotics. Across 31 trials and 8,672 participants it occurred in 1.5 per cent of the probiotic groups and 4.0 per cent of controls, again with moderate certainty. The benefit was concentrated in trials where the baseline risk was above 5 per cent, which describes hospital patients more than a healthy adult on a short course at home.

For treating acute infectious diarrhoea, the picture has changed. The 2020 Cochrane review included 82 trials and 12,127 participants, mostly children. In the large trials at low risk of bias, probiotics probably made little or no difference to the number still unwell at 48 hours, and the authors were uncertain whether duration was shortened at all. Fluids and oral rehydration remain the treatment, as what to eat in loose motion explains.

What about irritable bowel syndrome and everyday gut health?

The evidence here is suggestive and unsettled. A 2018 systematic review found 53 randomised trials of probiotics in 5,545 adults with irritable bowel syndrome. Particular combinations and strains appeared to help overall symptoms and abdominal pain, but the authors could not draw definitive conclusions and wrote that which combination, species or strain works remains for the most part unclear. For a healthy adult hoping for better digestion or immunity, the reviews read for this entry offer no trial result to quote. Food-first approaches are set out in the Indian IBS diet chart.

A worked example: a child's antibiotic course in Pune

This case is an illustration, not a real family. A six-year-old in Pune, otherwise healthy, is prescribed a seven-day antibiotic for an ear infection. The parent has a sachet from the chemist labelled 2 billion CFU of a named Lactobacillus rhamnosus strain and wants to know what the trial figures mean.

How do you read a probiotic label in India?

Start with the two capitalised phrases FSSAI requires, PROBIOTIC FOOD and NOT FOR MEDICINAL USE, and then look for the three facts that let you connect the pack to any evidence: the full name down to the strain, the live count at the end of shelf life, and the serving that delivers it. A pack that names only a genus, gives its count at manufacture, or promises to prevent or treat a disease falls short of the regulation.

Common mistakes and myths about probiotics

Four mistakes recur. The first is treating all probiotics as one thing, when the guidelines insist that effects are strain specific. The second is buying on the CFU number alone; the count matters only for a strain with evidence at that count. The third is expecting a sachet to treat a stomach infection, which the largest review does not support. The fourth is ignoring storage: the label rule on temperature exists because the organisms have to be alive on the last day of shelf life.

Safety, risks and when to see a doctor

In generally healthy children and adults the record is reassuring. In the 2019 children's review, none of the 24 trials that reported adverse events found a serious one attributable to probiotics, and the common complaints were rash, nausea, gas, bloating and constipation. The 2017 review listed abdominal cramping, nausea, fever, soft stools, flatulence and taste disturbance in both probiotic and control groups.

The serious harms sit in very ill people. The FAO/WHO report lists four theoretical risks, including systemic infection, and records cases of bloodstream infection in patients with underlying conditions. A 2019 study in intensive care found a markedly higher risk of Lactobacillus in the blood among patients given probiotics and matched the blood isolates genetically to the capsule. The pancreatitis trial ended with more deaths in the probiotic group and nine cases of bowel ischaemia against none.

Ask a doctor before taking a probiotic supplement if you have a weakened immune system, are on chemotherapy or immunosuppressant medicines, have a central venous catheter, pancreatitis or any serious illness, or if the person is a premature or hospitalised baby. See a doctor for diarrhoea with blood, high fever, signs of dehydration, or symptoms lasting more than a few days. A probiotic is not a substitute for oral rehydration or for a prescribed medicine, and no one should stop an antibiotic because of it.

NNWA courses that cover probiotics

Probiotics, prebiotics and fermented foods are taught in NNWA's Gut Health course, and the rules and evidence behind any supplement in Dietary Supplements and Nutraceuticals. NNWA, a private skill academy in Kolkata, runs its teaching online in Hindi and English. The courses prepare learners to coach healthy clients and to send medical cases to a doctor, and none of them is a degree or a dietitian qualification.