Gut Health, Probiotics and Dahi: What Actually Helps Your Gut Microbiome

The gut microbiome — the trillions of bacteria and other microbes living mainly in the large intestine — is linked in research to digestion, immunity, inflammation and much more. That has made 'gut health' a huge market. Much of what is sold, though, runs well ahead of the evidence, while the cheapest options are already in a desi kitchen.

What is the difference between probiotics and fermented foods?

A probiotic, by the international definition agreed by an expert panel in 2014, is a live microorganism that, given in adequate amounts, gives a proven health benefit. That benefit has to be shown for the specific strain. Fermented foods — dahi, lassi, kanji, kefir, idli batter, some pickles — are foods made by microbes. Many contain live bacteria, but they are not 'probiotics' in the strict sense unless a particular strain has been tested. Both can be useful; they are simply not the same thing.

Are fermented foods good for your gut?

The best trial so far says yes. In the 2021 Stanford study in Cell, 36 healthy adults were randomly assigned to eat either more fermented foods or more fibre for 17 weeks. The fermented-food group's microbiome diversity rose steadily and markers of inflammation in the blood fell. The high-fibre group's bacteria became better at breaking down fibre, but diversity did not change over the study. It was a small trial, but it fits a wider picture: regular fermented foods seem to help, and they are cheap and safe for most people.

How many different plants should you eat a week?

Variety seems to matter. The American Gut project, a citizen-science study of more than 10,000 people mainly in the US, UK and Australia, found that people who ate more than 30 types of plants a week had more diverse gut bacteria than people who ate 10 or fewer, regardless of whether they called themselves vegetarian. This is observational, but 30 is easier than it sounds in a desi kitchen: every spice, herb, daal, vegetable, fruit, nut, seed and grain counts. Haldi, zeera, dhania, adrak, lehsan, palak, tomatoes, onions, three kinds of daal and a few fruits already make 15.

Do probiotic supplements work?

For some specific uses. The clearest is preventing diarrhoea from antibiotics in children: a 2019 Cochrane review of 33 trials (6,352 children) found it fell from 19 percent to 8 percent, with higher doses (at least 5 billion colony-forming units a day) working better. For most other conditions the evidence is weaker or mixed. The American Gastroenterological Association's 2020 guideline recommends using probiotics for conditions such as irritable bowel syndrome, Crohn's disease, ulcerative colitis and C. difficile infection only within clinical trials, with a few specific exceptions. Healthy people with no gut symptoms have little reason to take them.

Should you take probiotics after antibiotics?

Not automatically. A small 2018 study in Cell found that, in adults after a course of antibiotics, taking a multi-strain probiotic delayed the return of their own normal gut bacteria compared with letting the gut recover on its own. For children, as above, probiotics reduce diarrhoea. For adults, ask your doctor; eating dahi, fibre and a variety of plants after antibiotics is a sensible, low-risk default.

What about gut cleanses, detox teas and kombucha?

• Gut 'cleanses' and detox teas are often laxatives. They empty the bowel, not 'reset' it, and can cause dehydration.
• Kombucha is a fermented tea; it is fine to drink but not proven to be better than dahi, and shop versions can carry a lot of sugar.
• Stool microbiome tests sold to consumers cannot yet tell you what to eat in a reliable, evidence-based way.
• Fibre supplements such as ispaghol (psyllium) are useful for constipation and cholesterol — that has good evidence.

When gut symptoms need a doctor

• Blood in the stool or black, tarry stools.
• Unexplained weight loss, ongoing vomiting, or difficulty swallowing.
• A lasting change in bowel habit, especially over age 45–50.
• Severe or worsening abdominal pain, or pain that wakes you at night.
• Diarrhoea lasting more than a few days, or with fever or dehydration — very common in Pakistani summers and important to treat with oral rehydration salts.
• Anaemia, which can come from slow bleeding in the gut.

This article is general information, not medical advice. People with a weakened immune system, serious illness, or a central line should not take probiotic supplements without their doctor's advice. See a doctor for any of the gut warning signs above.