Are probiotics necessary? Food expert Krish Ashok asks this question in his new book

Probiotics are supplements containing one or more named microbial strains. They are measured in colony-forming units, or CFU, which estimate how many organisms can still grow in laboratory conditions. The important difference is that these microbes arrive from outside, while your gut already contains a large resident community. A capsule is not simply refilling an empty tank.

The article compares the gut to an ecosystem. A probiotic may influence that ecosystem without becoming a major part of it. A 2018 Weizmann Institute study sampled the intestinal wall and found that a standard mixture settled briefly in some people but passed through others. Stool tests alone might not reveal that difference.

This makes broad claims about probiotics unreliable. A named strain may help with a particular problem, but another strain may do nothing. For healthy adults seeking vague “good gut health,” random daily capsules have weak evidence. The exact strain and goal matter more than a large CFU number.

The colon already houses tens of trillions of microbes from hundreds of species. A probiotic supplement may advertise a large number of organisms, expressed as colony-forming units, but that figure describes an estimate of laboratory growth capacity. It does not show how many organisms will survive, settle, or change the gut ecosystem.

The scale difference is central to the article’s argument. A capsule adds a relatively small group to an already crowded and complex community. Yet small groups can still affect an ecosystem without becoming its majority. The 2018 Weizmann Institute study demonstrated that the same probiotic mixture behaved differently in different people.

Therefore, counting organisms alone is not enough. The strain, the person, and the intended health goal matter. A large number on the label can create an impression of power, but it tells you little unless that exact strain has been tested for your specific problem.

A probiotic does not enter an empty container. It encounters a person’s existing microbes, intestinal environment, diet and other conditions. Because those ecosystems differ, the same newcomers may find temporary opportunities in one gut but fail to establish themselves in another. The article stresses that a capsule’s effects cannot be predicted from its label alone.

The 2018 Weizmann Institute study tested this directly. Researchers sampled the intestinal wall instead of relying only on stool. They found that a standard probiotic mixture briefly settled in some people. In others, it passed through like a visitor. This showed that probiotic behaviour can differ inside the gut, even when people take the same product.

The practical implication is that “probiotic” is too broad a description to predict results. The exact strains, the person, the illness and the health goal all matter. Marketing presents a general solution, but the biology is personal and strain-specific.

Antibiotics can disturb the gut’s existing microbial community. It may seem logical to replace lost microbes immediately with a probiotic capsule. But the article shows that this intervention can have an unwanted effect, because introducing selected strains is not the same as restoring the original ecosystem.

In the 2018 Weizmann Institute study, the particular probiotic mixture delayed the return of the original microbial community after antibiotics, compared with leaving the gut alone. The researchers also found that the mixture settled in some people and passed through others. This suggests that the same product can interact differently with different resident ecosystems.

The lesson is not that every probiotic is harmful after antibiotics. Some particular strains can modestly help with particular forms of antibiotic-associated or infectious diarrhoea. The lesson is that strain, illness, antibiotic and person all matter. “Take any probiotic after any antibiotic” is therefore unsupported.

Probiotics are not one treatment. The word covers many products containing different named microbial strains. Each strain may behave differently in the gut and may have been studied for a different outcome. Evidence therefore cannot be transferred automatically from one capsule, strain or illness to another.

The article gives a clear example. Particular strains can modestly help with some forms of antibiotic-associated or infectious diarrhoea. But another strain in another capsule may do nothing. The 2018 study also found that a standard mixture settled briefly in some people and passed through others, showing that the person matters as well.

This makes the first question practical: what problem are you trying to solve? For a healthy adult seeking a vague feeling of general gut health, evidence for a random daily capsule is weak. A product’s large CFU count or generic “immunity” claim cannot replace strain-specific evidence for a defined problem.

The article treats the microbiome as an ecosystem, not a tank that needs topping up. Resident microbes need suitable food, and fermentable plant foods provide a more dependable way to support them for most healthy people. This approach works with the community already present rather than assuming a capsule can rebuild it.

Foods such as rajma, dal, chana and vegetables supply fermentable material for resident microbes. The article compares this with restoring a degraded forest: improving the soil and allowing the native seed bank to work is more sensible than dropping a few potted plants from a helicopter. The food supports the ecosystem’s existing members.

This matters because capsules feel like active medical interventions, while fibre-rich meals seem ordinary. That active-intervention bias can make expensive products appear more powerful than everyday food. The article does not claim plant foods solve every gut problem, but presents them as a more dependable general strategy for healthy people than random probiotic capsules.

Fermented food is made through microbial activity, which can change flavour, texture, acidity and shelf life. A probiotic food, in the strict health sense, contains living microbes linked to a demonstrated benefit in a particular situation. Fermentation alone does not prove that every organism survives, reaches the eater alive or produces a health effect.

The article describes idli and dosa batter, pickles, kanji and ambali as foods transformed by lactic-acid bacteria and wild yeasts. Commercial dahi uses a defined starter culture for consistency, while home dahi carries forward whichever lactic-acid bacteria thrive in the previous curd. Heating can kill live cultures, and pasteurisation can remove living microbes after fermentation, depending on how the food is made and handled.

Therefore, “ancient probiotic” is an incomplete label. A fermented food may offer useful microbial activity, but its organisms and effects are not automatically standardised. Processing, storage and preparation determine whether live microbes remain when the food is eaten, while proven benefits still depend on the specific microbes and problem.