They are in pharmacies, along with vitamins C and multivitamin complexes. They are on the shelves of organic supermarkets, between adaptogens and turmeric shots. They occupy the reels of TikTok with the same enthusiasm with which before detox juices populated. Probiotics – supplements with live microorganisms that supposedly strengthen the intestinal flora – have become the health amulet of the 21st century. The promise is simple and seductive: take these “good” bacteria in a capsule and your gut, your brain, your immune system, and your skin will function better.
The business accompanies the promise. According to different estimates from the sectorthe global probiotics market was valued at around $114 billion in 2025 and is projected to continue growing at a sustained rate over the next decade. However, there is a problem that science has been contemplating for years: taken massively and indiscriminately, probiotic supplements not only do not improve the microbiome in the majority of healthy people. In some cases, they can actively block it.
A forgotten organ that regulates almost everything. The human intestine is home to trillions of microorganisms—bacteria, fungi, viruses—that form an ecosystem as complex and personal as a fingerprint. According to gastroenterologist Chris Dammanfrom the University of Washington, who has been studying the microbiome for 20 years, this ecosystem acts as “the gateway to the body’s overall health.”
Diets with more fiber, fruit and vegetables are those that generate the greatest variety and richness of bacteria in the intestine, and healthy bacteria produce short-chain fatty acids that support the health of the intestinal lining, according to the clinical documents of the Whole Health from the US Veterans Administration.
The microbiota is not just digestion. A review published in the journal Nutrients by researchers at the University of Cassino in Italy, details how the gut microbiota modulates neurochemical pathways involving serotonin, dopamine, GABA and glutamate, as well as the immune and endocrine axes. Microbial imbalance—what scientists call dysbiosis—contributes to low-grade systemic inflammation, impaired neuroplasticity, and altered stress responses, all of which are linked to mood disorders and cognitive decline.
However, the most striking fact is that Approximately 95% of the body’s serotonin is synthesized in the intestinenot in the brain. Whether the intestine is good or bad is no small matter. Take care of the microbiota is key to healthbut to make good use of probiotics it is important to first understand their real mechanism. And that’s where things get complicated.
Years of warning. The problem with probiotics is not that they never work. The thing is that we have turned them into a general use resource, something that is taken preventively and continuously, without diagnosis, without medical indication and without understanding what is really happening in each person’s intestine. A product with real and very specific benefits that social networks have turned into a universal solution.
Dammam explains it clearly: Probiotic supplements purchased without a prescription are not sufficiently regulated. You don’t really know what you’re taking. Products vary greatly in labeling accuracy, presence of adulterants, and legitimacy of their claims, according to VA Program documents. Prescribing probiotics is difficult even for doctors: there are thousands of products on the market, each claiming superiority over the other. Many have “special recipes,” proprietary strains or combinations of multiple organisms that the VA wryly describes as “a microbiological shotgun approach.” The problem, ultimately, is not just the lack of regulation. It’s that we start from a wrong premise.
The science behind. Dr. De la Puerta, an expert in microbiota, sums it up with a phrase that does not leave much room for interpretation: “If you want a healthy microbiota, you probably don’t need to live taking probiotics.” He said it in podcast by Dr. José Abellán in one of the most shared analyzes of intestinal health in recent weeks.
Her central argument is not that probiotics are useless—in fact, she herself admits that she uses and prescribes them frequently—but that they are becoming a permanent habit when they are designed to be a one-time tool. “You have to take them to get you out of a place,” he explains. And he gives his own case as an example: “My microbiota is fairly good, but I have a lot of stress. So I take probiotics from time to time.” The key is in those two words: seasons.
Deeper investigations. The latest science backs up exactly this nuance. A review published in Trends in Microbiology concludes that the composition of the microbiome varies greatly depending on geography, age and lifestyle, which directly calls into question the efficacy of universal probiotic treatments and requires that the design of any effective probiotic takes into account microbial diversity and specific adaptation to the context of each host. The Probiota 2025 conference, held in Copenhagen, confirmed this same idea: Geographic and demographic variations reveal microbiome profiles so different among healthy populations that it is impossible to define a universal standard of a “healthy microbiome.”
There is another equally serious problem, which Dr. De la Puerta points out precisely: not all probiotics are the same, even if we sell them as if they were. “Take a probiotic, stabilizer, immunomodulator, neuroactive, high load, low load, monostrain, multistrain…”, he lists. Some have more to do with the immune system, others with digestive health, others with mood. The most successful interventions are those informed by a microbial profile prior to treatment, which allows predicting therapeutic efficacy. “That’s why it doesn’t make much sense to buy them at random simply because someone has recommended them on social networks,” the expert details.
The garden already planted. There is a conceptual error that lies at the bottom of this entire debate. We take probiotics as if the intestine were empty land waiting to be repopulated. But in the vast majority of healthy adults, the intestinal ecosystem is already established and has its own defenses. According to the VA Programcontinuing to take them once a healthy intestinal ecosystem is formed would be like planting an already planted garden.
The real problem, in most cases, is not a lack of bacteria. The thing is that we are starving those we already have. What industrial food processing has eliminated from the diet may be depriving the microbiota of nutrients, Damman explains.: People focus on the nutrients their body needs when eating, but not so much on those needed by the bacterial community inside them. And the data is difficult to ignore: Only 5% of Americans consume the recommended daily amounts of fiber, with an average intake of just 16.2 grams versus the recommended 21-38. Instead of feeding the ecosystem they already have, they buy capsules for one that doesn’t exist.
What does work: the plate before the capsule. Dr. De la Puerta is direct: “It is of little use to spend money on probiotics if the diet is poor in fruits, vegetables and legumes, if we sleep poorly or if we live permanently stressed.” The microbiota “depends on the quality of the diet, fiber consumption, rest, stress, physical exercise and many other factors that are part of daily life.” You have to sit down and watch how you eat and how you live, he insists. There is no more.
The Stanford study published in cell compared two groups of healthy adults for ten weeks: a diet rich in fiber and another in fermented foods. The fermented group recorded a significant increase in microbiome diversity, a drop in levels of 19 inflammatory proteins in the blood, and lower activation in four types of immune cells. The high fiber group, on the other hand, did not increase microbial diversity, and participants with lower basal diversity even showed elevated inflammatory markers. Damman calls fermented foods “nature’s probiotic”: Bacteria come packaged with the foods they like and the bioactive molecules they produce.
Not all fermented products work the same. While conventional yogurt usually contains between 2 and 5 bacterial strains with transient effects on the intestine, kefir It is a symbiotic consortium which houses between 30 and 50 strains of bacteria and yeast. Its microbiological diversity allows it to survive stomach acids and establish itself persistently: the bacteria are not just passing through, but transform the bacterial flora. Its residual lactose level is also significantly lower, which explains why even people with lactose intolerance digest it better.
The panacea is not in the bottle. The history of probiotics is the story of how marketing managed to outrun science. It’s not that they are a fraud, it’s that we have oversimplified an extraordinarily complex system, packaged it, and put it on sale with promises that the evidence cannot generally support. The most holistic and sustainable strategies are those that preserve the intestinal ecosystem from withinnot those that try to replace it with supplements designed in market systems.
The focus should be on improving the ecosystem as a whole, so that the individual does not depend on bacteria in pill format. Dr. De la Puerta says it in the same terms, but with the frankness of someone who sees it every week in consultation: a healthy microbiota is not achieved only with supplements. “Every day is built with habits that feed the beneficial bacteria that already live in our intestine,” he concludes.
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