Consumers often think of probiotics — found in yogurt and other foods — as healthful but they can cause a significant accumulation of bacteria in the small intestine that can result in disorienting brain fogginess as well as rapid, significant belly bloating, investigators report.
In a published study of 30 patients, the 22 who reported problems like confusion and difficulty concentrating, in addition to their gas and bloating, were all taking probiotics. Some were taking several varieties.
When investigators looked further, they found large colonies of bacteria breeding in the patients’ small intestines, and high levels of D-lactic acid being produced by the fermentation of sugars in their food, said Dr. Satish S.C. Rao at the Medical College of Georgia at Augusta University.
“What we now know is that probiotic bacteria have the unique capacity to break down sugar and produce D-lactic acid. So if you inadvertently colonize your small bowel with probiotic bacteria, then you have set the stage for potentially developing lactic acidosis and brain fogginess,” Rao says.
D-lactic acid is known to be temporarily toxic to brain cells, interfering with cognition, thinking and sense of time. They found some patients had two to three times the normal amount of D-lactic acid in their blood. Some said their brain fogginess — which lasted from a half hour to many hours after eating — was so severe that they had to quit their jobs.
The report, published in the journal Clinical and Translational Gastroenterology, appears to be the first time the connection has been made between brain fogginess, bacterial overgrowth in the small intestine, high levels of D-lactic acid in the gut and probiotic use, Rao says.
Beneficial in some scenarios
While probiotics can be beneficial in some scenarios, like helping a patient restore his gut bacteria after taking antibiotics, the investigators advised caution against its excessive and indiscriminate use.
“Probiotics should be treated as a drug, not as a food supplement,” Rao says, noting that many individuals self-prescribe the live bacteria, which are generally considered good for digestion and overall health.
Other studies have also suggested that probiotics may not be helpful for all patients. In March 2017, a University of new South Wales team reported that probiotics are much less effective when taken alongside a balanced diet, and could even impair certain aspects of memory.
In that study, fat rats with poor gut health, thanks to being fed junk food, probiotics positively changed the bacterial make-up in their digestive tract and improved brain function, preventing spatial memory loss.
But for rats on a healthy diet, the probiotics had little impact on microbial diversity and actually impaired recognition memory. The team’s results were published in the journal Molecular Psychiatry.
“If you’re eating really badly then probiotics might be helpful. But if you’re already eating healthily, they may not be that beneficial,” said Professor Margaret Morris, Head of Pharmacology at UNSW, in a news release.
“Although this study is looking at rats, I think the main takeaway message is that we need to exercise caution when we recommend that people take probiotics.”
A July 2018 study from the University of Kansas published in PLOS One reviewed available research conducted on animals and people, finding evidence that probiotics can reduce anxiety in rodents, but not in humans.
“I think people should wait — that’s the best takeaway here,” said lead author Daniel J. Reis, a doctoral student of clinical psychology at KU. “We’re in the early days of this research into probiotics. I’ve seen a lot of stories hyping probiotics as helpful for anxiety. We’re not saying they do nothing, but we have a lot to figure out before we know if they can be used therapeutically. I wouldn’t recommend using probiotics to treat anxiety at this stage.”
Reis and his colleagues reviewed data from 22 preclinical studies involving 743 animals and 14 clinical studies of 1,527 individuals, finding that “Probiotics did not significantly reduce symptoms of anxiety in humans and did not differentially affect clinical and healthy human samples.”
About the study
In the Georgia study, all patients experiencing brain fogginess took probiotics and SIBO was more common in the brain fogginess group as well, 68 percent compared to 28 percent, respectively. Patients with brain fogginess also had a higher prevalence of D-lactic acidosis, 77 versus 25 percent, respectively.
Those with brain fogginess reported a tremendous increase in their abdominal size within just a few minutes of eating. When brain-foggy patients stopped taking probiotics and took a course of antibiotics, their brain fogginess resolved.
Movement of food through the gastrointestinal tract was slow in one third of the brain-foggy patients and one fourth of the other group. Slower passage, as well as things like obesity surgery, can increase the chance of bacterial buildup, or SIBO.
“Now that we can identify the problem, we can treat it,” Rao says. Diagnosis includes breath, urine and blood tests to detect lactic acid, and an endoscopy that enables examination of fluid from the small intestines so the specific bacteria can be determined and the best antibiotics selected for treatment.