Researchers are starting to raise concerns about routine daily intake of probiotics for "gut health". Much is still unknown, but problems are starting to appear. A healthy gut contains hundreds of species (bacteria, fungi, viruses), and taking megadoses of a few species (a probiotic supplement) can overwhelm the normal gut microbial community. A healthy gut is one with a greater diversity of species, not just some species.
For example, one study found that daily probiotic ingestion can result in overgrowth of some bacterial species in the intestines, resulting in such symptoms as brain fogginess, bloating, and gas. Successful treatment was antibiotics and stopping the use of probiotics. Another recent study found that after using antibiotics, those who took probiotics (thinking it would help microbial recolonization of the gut microbes) actually had slower recovery of the gut microbiome (microbial community). The best recovery was in those who took nothing, no supplements at all, or those who received a fecal microbial transplant (where an entire microbial community is transplanted).
The evidence is showing that for gut microbial health, the best thing to do is eat a variety of real whole foods (and not highly processed foods) that have lots of fiber, such as whole grains, fruits, vegetables, seeds, nuts, and legumes (beans). In other words, feed the beneficial bacteria. A Mediterranean style diet is good.
A recent article in Medscape (the medical site) highlights these same concerns. [See below.] A study that looked at the gut microbiome of people who were about to undergo treatment for melanoma found that those who were taking probiotics actually had worse gut microbial diversity. [Remember, gut microbial diversity is considered an indicator of gut health.] And the cancer treatment (immunotherapy) did not work as well on them.
Bottom line: The evidence is showing that for gut microbial health, the best thing to do is eat a variety of real whole foods (and not highly processed foods) that have lots of fiber, such as whole grains, fruits, vegetables, seeds, nuts, and legumes (beans). In other words, feed the beneficial bacteria. A Mediterranean style diet is good. Don't take routine daily supplements or probiotics for "gut health" - they won't help. Instead, if you want - only take probiotics for a short while for a specific symptom or problem.
Dr. Lorenzo Cohen wrote a piece for the Wall Street Journal laying out those same points. Excerpts from: Those Probiotics May Actually Be Hurting Your ‘Gut Health’
... I started eating and drinking more foods that are rich in probiotics. My gastrointestinal tract felt great and everything was going along smoothly (pun intended). I assumed that the kinds of bacteria in these foods increased the diversity of my microbiome, as each one would contribute something different. But I could find little actual information available to make certain of that: Probiotics may list multiple bacteria in their ingredients, but they usually come from no more than five different major strains and often only the same two, Lactobacillus and Bifidob
I also stopped eating refined carbohydrates (white flour, white rice, etc.) and ate less whole grains, because I wanted to lower my overall glycemic load. ...
After about six months of this modified diet, I expected my gut microbiome to be in great health. Instead, to my shock, its diversity was less than before I started the diet. I had actually made the health of my microbiome worse.
My personal results were mirrored by a study that our MD Anderson team had just presented at an international meeting. The provocative findings received a lot of publicity. The preliminary results showed that patients who reported taking an over-the-counter probiotic supplement had a lower probability of responding to immunotherapy as well as lower microbiome biodiversity. But those eating a high-fiber diet were about five times more likely to respond to immunotherapy and had high gut bacteria diversity, including bacteria previously linked to a strong immunotherapy response.
It turned out that taking an over-the-counter probiotic pill could inadvertently decrease microbiome biodiversity. A study last year from Israel’s Weizmann Institute of Science similarly found that taking an over-the-counter probiotic supplement delayed reconstitution and recovery of the gut microbiome in mice and humans after antibiotic treatment.
To get my microbiome back on track, I reduced the probiotic-rich foods I was eating and drinking and I started to add more fermentable fibers from healthy whole grains like oats, buckwheat and barley and from seeds such as hemp, flax and chia. The results were startling. Not only did the diversity increase, the change completely reversed the negative effect of the probiotics-rich, low whole-grain diet and even improved my gut health over my previous vegan diet.
In my case, we do not know for sure what caused the increase in biodiversity—decreasing the probiotic-rich foods, increasing healthy whole grains and seeds, or a combination of both. It’s possible that too much consumption of a narrow band of probiotics may disrupt an otherwise diverse and healthy microbiome. Or it may be more important to keep up the consumption of grains because they are the main food source for beneficial bacteria. What we do know is that a low-fiber diet is associated with low biodiversity and a scarcity of healthy bacterial species, and that the microbiome flourishes with a high-fiber diet that includes fermentable fibers from whole grains and other foods.
The market for probiotic-rich designer foods is huge, and the supplement industry and technologies to manipulate the microbiome are ever-expanding. Yet I now believe that the cheapest and safest way to improve our microbiome and gut health is to make simple dietary changes to feed the development of good bacteria and crowd out the bad. There is no pill, special food, unique diet or quick fix for what ails our health and diet. The key is simply to focus on eating a diverse, whole-food, plant-centered, high-fiber diet.
Excerpts from Medscape: Harnessing the Power of Microbes to Fight Cancer
Probiotics, traditionally perceived to be good for the gut and overall health, may not be the best choice in patients with cancer. The surprising preliminary findings of a recent study in patients with melanoma indicate that users of over-the counter (OTC) probiotics have one-third the odds of responding to immunotherapy treatment with anti-programmed cell death-1 checkpoint inhibitors compared with patients not taking probiotics.
"What we found is that patients who are taking probiotics have decreased diversity of the microbiome, a key measure of overall gut health, and seem to have a decreased response to immunotherapy," said Jennifer McQuade, MD, MS, MA, LAc, medical oncologist with the University of Texas MD Anderson Cancer Center in Houston.
While such a dramatic decrease in the efficacy of immunotherapy in probiotic users may come as a surprise, a close link between the gut microbiome composition and the efficacy of cancer therapies has already been established in numerous human and animal studies. Microbiome patterns associated with improved response to cancer immunotherapies have been identified, prompting researchers to more closely examine the microbiome signatures of individuals who responded to treatment.
Their findings indicate that at the initiation of cancer therapy, a significant number of patients are already taking OTC probiotics. "We found that 42% of our patients use over the counter probiotics, which is probably the result of people reading about the gut microbiome's influence on immunotherapy response and hoping that a probiotic pill is an easy way to manipulate it," said McQuade.
Although this was not a controlled study, and patients took unselected probiotics, the findings pointing to decreased microbiome diversity in probiotic users were in line with an earlier study showing impaired microbiome reconstitution due to probiotic use.
"This is basically competitive exclusion at play, where you are overwhelming the system with a few strains of bacteria and damaging the overall healthy ecosystem," she continues. "I now ask my patients about probiotic use and, if they are using probiotics, I specifically ask them to discontinue."
When McQuade and colleagues analyzed the connection between dietary fiber and response to immunotherapy in a subset of patients with melanoma who consumed a fiber-rich diet, the findings were eye opening.
Keep in mind that while this study was done in cancer patients, the findings of daily supplementation of probiotic supplements on gut microbiome (microbial community) diversity applies to all of us. Bombarding the gut microbial community with billions of a few bacterial species (the probiotic) for days has negative effects on the microbial community.
From the Parker Institute for Immunotherapy: Probiotics Linked to Poorer Response to Cancer Immunotherapy in Skin Cancer Patients
Overall, Parker Institute and MD Anderson researchers found that diet and supplements appear to have an effect on a patient’s ability to respond to cancer immunotherapy, most likely due to changes in the patient’s gut microbiome. Among the findings:
- Over-the-counter probiotic supplement use was linked to a 70% lower chance of response to immunotherapy with anti-PD-1 checkpoint inhibitors in a subset of 46 melanoma patients
- 42% of all patients reported taking over-the-counter probiotics among those who took the lifestyle survey
- Probiotics were linked to lower gut microbiome diversity, previously shown to be associated with poorer response to anti-PD-1 checkpoint inhibitors
- Patients eating high-fiber diets were about 5 times as likely to respond to immunotherapy treatment with anti-PD-1 checkpoint inhibitors
- Patients eating diets rich in whole grains had more bacteria associated with positive response to checkpoint immunotherapy
- Diets high in processed meat and added sugar had fewer bacteria associated with a positive response to checkpoint immunotherapy
“Eating a high-fiber diet has long been shown to have health benefits. In this case, we see signs that it is also linked to a better response to cancer immunotherapy,” Spencer said. “Definitely another good reason to load up on whole grains, vegetables and fruits.”