We carry a lot of microbes around with us, and the ones in our gastrointestinal tract can have a big impact on our health. That’s led to the wide availability of probiotic supplements, which aim to boost the bacteria in the gut. As a sales pitch, these probiotics are meant to have good effects on health. But new research suggests that these supplements should be used with caution; it appears they can cause some serious side effects. In this study, the sample size was relatively small, but in a group of 30 people, the 22 that were having difficulty concentrating and reporting confusion, as well as gas and bloating, were also taking probiotics.
The researchers investigated that correlation and found that vast numbers of bacteria were taking up residence in the small intestines of people taking probiotics. Lactobacillus bacteria were fermenting the sugars in what people ate, and in the intestine, the bacteria were generating lots of D-lactic acid, said 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.
D-lactic acid disrupts brain cell function and can cause trouble with the perception of time, and cognition. In some of these individuals, they could not work anymore because of their brain fog, which could last for hours. They were found to have two or three times the normal level of D-lactic acid in their blood.
"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 said. This work, published in Clinical and Translational Gastroenterology, is probably the first report of a link between intestinal bacterial overgrowth, D-lactic acid levels, and cognition difficulties.
"Probiotics should be treated as a drug, not as a food supplement," Rao noted.
Probiotics have previously been shown to cause overproduction of D-lactic acid in patients with a short bowel, which is dysfunctional. Small intestinal bacterial overgrowth, SIBO, is a known problem in these patients. The risk of SIBO also goes up when food moves too slowly through the intestine, which was seen in a third of patients who had brain fog. The production of gas by those bacteria may also explain the bloating.
"Now that we can identify the problem, we can treat it," Rao said. In this case, it’s probiotics that are encouraging bacteria to grow. After probiotic use was discontinued and the patients were treated with antibiotics, their symptoms subsided. Afterwards, 70 percent of patients said symptoms were significantly improved; 85 percent said they no longer had brain fog.
Probiotics can still help people with gastroenteritis that wipes out their gut microbes. "In those situations, we want to build up their bacterial flora so probiotics are ideal," Rao said.
There is still a lot more work to be done to understand what’s happening in the gut. It seems that one should exercise caution when messing with gut microbes. "I think the small bowel can be a source of huge mystery," Rao said.
Rao noted that some foods are still healthy probiotics, like kimchi, yogurt, sauerkraut, and dark chocolate. They don’t contain much bacteria and should be safe for most people.
Learn more about the connection between gut microbes and brain function from the video.