As several studies have revealed the importance of having a thriving gut microbiome, many people have begun taking probiotic supplements as a way to enhance their mental and physical health. But are probiotics for everyone, and can they cause health issues in certain populations?

A new study, published in the journal Clinical and Translational Gastroenterology, finds that in some people, probiotic use can inadvertently lead to a significant accumulation of bacteria in the small intestine. This extra bacteria is often tied to disorienting brain fogginess as well as rapid, significant belly bloating.

Those at risk may include patients with diabetes, short bowel syndrome or slow motility, and those taking certain drugs such as opioids or proton pump inhibitors.

In a study of 30 patients, the 22 who reported health issues such as confusion and difficulty concentrating, in addition to their gas and bloating, were all taking probiotics. Some participants were taking several varieties.

When researchers investigated the issue further, they discovered large colonies of bacteria breeding in the patients’ small intestines (probiotic supplements target the colon, not the small intestine), and high levels of D-lactic acid being produced by the bacteria lactobacillus’ fermentation of sugars in their food.

D-lactic acid is known to be temporarily toxic to brain cells, interfering with cognition, thinking and one’s sense of time. The researchers discovered that some patients had two to three times the normal amount of D-lactic acid in their blood. Some of the participants 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 appears to be the first time the association has been made between brain fogginess, bacterial overgrowth in the small intestine, high levels of D-lactic acid in the gut and probiotic use, says Dr. Satish S.C. Rao, director of neurogastroenterology/motility and the Digestive Health Clinical Research Center 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.

Probiotics can certainly be beneficial in many cases, such as helping a patient restore his gut bacteria after taking antibiotics, but the researchers advise against excessive and indiscriminate use.

Previously, probiotic use has been implicated in the production of D-lactic acid and brain fogginess in patients with short bowel syndrome as their small intestine does not function properly. This can happen in some newborns fed formula containing probiotics.

Short bowel syndrome results in a lot of undigested carbohydrates that are known to cause small intestinal bacterial overgrowth, or SIBO, and the high levels of D-lactic acid. Severe liver and kidney problems can produce similar problems.

The findings show that all patients experiencing brain fogginess had been taking probiotics. 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.

When the patients with brain fog 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 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 allows examination of fluid from the small intestines so the specific bacteria can be determined and the best antibiotics selected for treatment.

Typically there is not much D-lactic acid made in the small intestines, but probiotic use appears to change that. SIBO, which was present in most of the participants with brain fogginess, can cause bacteria to go into a feeding frenzy that ferments sugars resulting in production of uncomfortable things like hydrogen gas and methane that explain the bloating.

After treatment, 70 percent of patients reported significant improvement in their symptoms and 85 percent said their brain fogginess was gone. Those without brain fogginess but with SIBO and high levels of D-lactic acid reported significant improvement in symptoms like bloating and cramping within three months.

Probiotic use may be particularly problematic for people who have known problems with motility, as well as those taking opioids and proton pump inhibitors, which reduce stomach acid secretion and so the natural destruction of excessive bacteria.

Probiotics are supposed to work in the colon and not the small intestines or stomach, Rao says, so motility issues can result in problems with probiotic bacteria reaching the proper place. A wide variety of problems, from conditions like diabetes to drugs like antidepressants and minerals like iron, can slow movement and increase the possibility that probiotics will remain too long in the upper gut where they can cause harm, he says.

Probiotics definitely can help, for example, people who have gastroenteritis, or stomach flu, or are left with diarrhea and other problems after antibiotics wipe out their natural gut bacteria, Rao says.

“In those situations, we want to build up their bacterial flora so probiotics are ideal,” he says.

Source: Medical College of Georgia at Augusta University