‘Gut Health’ Has a Fatal Flaw

In my childhood home, an often-repeated phrase was “All disease begins in the gut.” My dad, a health nut, used this mantra to justify his insistence that our family eat rice-heavy meals, at the exact same time every day, to promote regularity and thus overall health. I would roll my eyes, dubious that his enthusiasm for this practice was anything more than fussiness.

Now, to my chagrin, his obsession has become mainstream. Social-media testimonials claim that improving your “gut health” not only helps with stomach issues such as bloating and pain but also leads to benefits beyond the gastrointestinal system (easing problems including, but not limited to, itching, puffy face, slow-growing hair, low energy, acne, weight gain, and anxiety). You can now find a staggering range of products claiming to support digestive health: Joining traditionally gut-friendly fermented foods such as yogurt and sauerkraut are “probiotic” or “prebiotic” teas, cookies, gummies, supplements, powders, and even sodas.

The reality is less straightforward. Maintaining the health of the gastrointestinal tract, like the health of any body part, is always a good idea. But expecting certain foods and products to overhaul gut health is unrealistic, as is believing that they will guarantee greater overall well-being. Those claims are “a little bit premature,” Karen Corbin, an investigator at the Translational Research Institute of Metabolism and Diabetes, told me. Obsessing over it just isn’t worth the trouble, and can even do more harm than good. “Gut health” cookies, after all, are still cookies.

In my dad’s defense, your gut does matter for your health. A massive microbial civilization lives mostly along the large intestine, helping the body get the most out of food. Broadly, a healthy gut is one where the different segments of this population—numerous species of bacteria, fungi, and viruses—live in harmony. An unhealthy one implies a disturbance of the peace: One group may grow too powerful, or an invading microbe may throw things off-balance, leading to problems including gastroenteritis and a compromised immune system.

Diet in particular has a profound impact on the gut—and how it subsequently makes you feel. “Food can have effects on the microbiome, which can then secondarily affect the host,” Purna Kashyap, a gastroenterologist at the Mayo Clinic, told me. The effects of food on a person and their microbes, he added, are generally congruent; fast food, for example, is “bad for both of us.” Neglect to feed your microbiome and the balance of microbes could tip into disarray, resulting in an imbalanced gut and corresponding bloating, stomach pain, and problems with bowel movements.

Fermented foods such as yogurt and kimchi, long considered good for digestive health, are known as “probiotics” because they contain live bacteria that take up residence in your gut. Other foods are considered “prebiotic” because they feed the microbes already in your gut—mostly fiber, because it isn’t digested in the stomach. Getting more fiber improves regularity and supports a more normal GI system, Corbin said.

But the fundamental problem with the gut-health obsession is that “there’s no clear definition of a healthy gut microbiome,” Corbin said. The makeup and balance of people’s microbiomes vary based on numerous factors, including genes, diet, environment, and even pets. This means that a treatment that works to rebalance one gut might not work for another. It also means that a product promoting a healthy gut doesn’t mean anything concrete. The idea that achieving gut health, however it’s defined, can solve stomach-related issues is misguided; many diseases can cause abdominal distress.

Less certain is how much gut health is responsible for benefits beyond the gastrointestinal tract. No doubt the microbiome is connected to other parts of the body; recent research has suggested that it has a role in weight gain, depression, and even cancer, supporting the idea that having a healthy gut could lead to other benefits. But the mechanisms underpinning them are largely unknown. Which microbes are involved? What are they doing? There are “a lot of tall claims based on animal studies that the microbiome influences diabetes or obesity or whatever,” and the translatability of those studies to humans is “really unlikely,” Daniel Freedberg, a gastroenterologist at Columbia University, told me. Until scientists can show definitively that microbe X leads to outcome Y, Corbin said, any relationships between the gut and overall health are “just correlations.”

None of this is to say that paying more attention to your digestive health is a bad idea. Especially for people diagnosed with gastrointestinal problems like IBS or Crohn’s disease, it can be essential. For everyone else, pursuing a healthy gut with food and supplements can be a nonspecific process with poorly defined goals. The food industry has capitalized on interest in probiotics and prebiotics—as well as lesser-known postbiotics and synbiotics—making products such as “insanely probiotic” yogurt, probiotic-fortified chocolate and spaghetti, and prebiotic sodas. Particularly with probiotics, the specifics are lacking. Which bacteria, and how many of them, actually make it past the stomach into the colon isn’t well understood. “A lot of probiotics are unlikely to contain viable bacteria, and probably very few of them are really making it through to the colon,” Freedberg said.

Prebiotics are generally more important, although the source matters. Prebiotic fiber is “one of the most important things that determines what bacteria are there,” Freedberg told me, but getting small amounts from fiber-fortified products isn’t going to make a huge difference. The soda brands Poppi and Olipop largely contain inulin, a type of fiber that’s common in food manufacturing for its slightly sweet taste, Freedberg explained, though it probably doesn’t contain a lot, otherwise it would become “sludgy.” Olipop contains about nine grams of fiber per can, roughly the same amount as one cup of cooked lima beans.

Of course, any product that is inherently unhealthy won’t magically become good for you the moment fiber or live bacteria are added to it. With desserts and salty snacks, no amount of fiber “is going to overcome the issue” that they are full of sugar or salt, Corbin said. Concerns about medium aside, though, gut-health products elicited a shrug from her: Buying foods containing additional prebiotic fiber is a “reasonable approach,” so long as they’re healthy to begin with. If probiotics make a patient feel “fantastic,” Freedberg said, “I’m not going to rock the boat.” Prebiotic and probiotic products may help to a degree, but don’t expect them to overhaul an unhealthy gut one soda at a time. All of the experts I spoke with said that people concerned about their gut health should eat a lot of fruits, vegetables, whole grains, and legumes, and cut out junk that won’t feed their microbiome. In other words, a basic healthy diet is more than enough to achieve good gut health.

My dad’s gut-health mantra was apparently borrowed from Hippocrates, suggesting that people have been obsessing over the digestive system for thousands of years with the belief that it is the key to overall health. The draw of this idea is its simplicity: Proposing that the body’s many ills can be collapsed into a single mega-ailment makes treatment seem refreshingly uncomplicated compared with the medical interventions needed to address individual problems. That the proposed treatments are easy and self-administrable—sipping fibrous soda, popping bacteria-packed pills—adds to the appeal.

But perhaps what is most compelling about the idea is that there is some truth to it. Lately, research on the microbiome has seen some promising advances. A large study published in 2022 showed significantly elevated levels of certain bacteria in people with depressive symptoms. Another study, co-authored by Corbin in 2023, was one of the first to show, in a human clinical trial, that a high-fiber diet shifts the microbiome in a way that could promote weight loss. This moment is especially confusing because we are finally beginning to understand the gut’s connections to the rest of the body, and how eating certain foods can soothe it. Much more is known about the gut than in the days of Hippocrates, but still far less than the gut influencers on social media would have you believe.