Do Probiotic Supplements Cause Brain Fog?

Do you take probiotic supplements? Probiotic supplementation has become popular in recent years, but new research from Augusta University suggests that it may come with unexpected side effects.

Researchers found that the ongoing use of probiotic supplements can lead to brain fogginess and intestinal bloating. After investigating how probiotic supplementation affects your gut, the research team recommended taking probiotics only under certain conditions rather than indiscriminately as a health supplement.

Letís take a closer look at their findings and recommendations.


The study, published in Clinical and Translational Gastroenterology, investigated whether or not brain fogginess, gas and bloating were related to small intestinal bacterial overgrowth (SIBO).

The study included 30 people who were experiencing brain fogginess, including difficulty with concentration, impaired judgement, confusion and poor short-term memory. All these people were taking probiotic supplements. They were compared to a control group of 8 people who did not have brain fog, and only one person in this group was taking probiotics.

Researchers found unusually large colonies of bacteria breeding in the small intestines of those with brain fog. These bacteria were also producing large amounts of D-lactic acid, an organic acid produced by certain bacteria as they break down sugar during fermentation.

D-lactic acid is typically produced by bacteria in the large intestine in small amounts. But the researchers discovered that bacteria from probiotic supplements have the unique ability to break down sugar and produce D-lactic acid in the small intestine. This means if you colonize your small bowel with probiotic bacteria, this can lead to excessive levels of D-lactic acid in your body, also called D-Lactic acidosis.

Some of the participants had two to three times the normal amount of D-lactic acid in their blood. D-lactic acid is known to be temporarily toxic to brain cells when levels become too high in your body. It can interfere with cognition, thinking and sense of time.

The participants said their brain fogginess and bloating would start soon after eating, and could last for many hours. Researchers believe this was likely due to the excessive bacteria in their small intestines producing a surge of D-lactic acid as the bacteria fermented the sugars in their food. This would also result in the production of by-products like methane and hydrogen gas, which could explain the bloating.

All participants were asked to stop taking probiotic supplements during the study. In addition, participants with evidence of SIBO and/or D-lactic acidosis were given antibiotics that targeted their overgrown bacterial populations.

Following treatment, 70 percent of participants reported significant improvement in their overall symptoms, and 85 percent reported complete resolution of brain fog. Researchers felt this was further evidence that the symptoms of brain fog and intestinal bloating were linked to D-lactic acidosis and SIBO from probiotic supplementation.


The researchers recognized that probiotic supplementation can be beneficial in certain situations, such as helping a patient restore their gut bacteria after taking antibiotics. But they advised against taking probiotics indiscriminately. They felt probiotics should be treated as a drug, not as a food supplement.

The National Institutes of Health (NIH) has similar recommendations. They cite research showing that probiotic supplements can help prevent or treat conditions such as irritable bowel syndrome, tooth decay, colic in infants and certain allergic disorders like hay fever.

But the NIH also states that ďstrong scientific evidence to support specific uses of probiotics for most health conditions is lacking.Ē They point out that we still do not know which probiotics are helpful and which are not, or exactly how each strain of bacteria affects our bodies.

Limited research has been done on the long-term safety of probiotics, and it may be different for each person. Research has already shown that probiotic supplementation can lead to severe side effects, such as dangerous infections, in people with underlying medical conditions, such as a weakened immune system or critical illness.

Also, the studyís discovery that probiotic supplements can change the flora in your small intestine is an area of concern. The helpful gut bacteria that promote a healthy microbiome live primarily in your large intestine, and thatís where probiotics are supposed to go.

But this study shows that probiotics can get stuck in the small intestine and cause problems. This may be especially problematic in those with impaired motility, which can result from conditions like diabetes or high iron levels.

Itís best to speak to your doctor before starting probiotic supplementation. You can ask if any health issues you may have could benefit from probiotics. And if youíve been taking probiotics for a while, pay attention to whether or not youíve had issues with concentration, focus, intestinal bloating or gas.

If youíve experienced anything unusual, speak to your doctor about it. They can order tests to check your current digestive health and recommend a course of action, such as stopping your probiotics for a while to see if your symptoms improve.


Keep in mind that probiotic supplements are a modern invention. They are commercially produced to contain precise amounts of specific strains of bacteria. This is very different than probiotic-rich foods, such as sauerkraut and miso, that have been fermented using traditional methods.

These typically contain a range of bacteria in varying amounts. And fermentation expert Sandor Ellix Katz suggests this is exactly what makes fermented foods so safe. In his book, The Art of Fermentation, he points out that fermentation relies on the diversity of beneficial bacteria to create an environment too acidic for harmful bacteria to survive.

Probiotic-rich foods have been made and consumed safely for thousands of years. They have many important health benefits and are one way to help maintain a healthy gut biome.

Even the researchers of the study still recommended eating probiotic-rich foods. They pointed out the fact that fermented foods are generally safe because they have much smaller amounts of bacteria present in a serving than probiotic supplements.

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Helen C
Helen C5 months ago


Louise A
Lara A5 months ago

thank you

Frances G
Past Member 5 months ago

Thanks for posting

Anna R
Anna R5 months ago

thank you for sharing

Sophie A
Past Member 5 months ago


Daniel N
Past Member 6 months ago

thanks for sharing

Victoria P
Victoria P6 months ago

Thank you

hELEN hEARFIELD6 months ago


Gino C
Past Member 6 months ago

Thank you

heather g
heather g6 months ago

1t Apple Cider Vinegar in a glass of water before meals may also clear brain fog. It worked for me....