And bad gas and diarrhea, according to a new study

By Mike Pomranz
Updated August 08, 2018
Credit: Photo by Douglas Sacha via Getty Images

Probiotics are a “good” bacteria that are supposedly able to alleviate all sorts of ailments. But the extent to which taking additional probiotics can be beneficial has long been up for debate. And now, recent research suggests that, in some people, excessive use of these kinds of supplements can actually cause negative side effects from the somewhat obvious—like gas, bloating, and diarrhea—to a far more disconcerting condition known as “brain fog.”

This possible connection between probiotics and brain fog comes courtesy of a team of gastroenterologists from Augusta University in Georgia. As they explain in their paper, published earlier this year in the journal Clinical and Translational Gastroenterology, brain fogginess “describes a constellation of symptoms comprised of mental confusion, impaired judgment, poor short-term memory, and difficulty with concentration, which is often transient and disabling.” As one researcher involved with the study, Statish Rao, explained to the site Gizmodo, his team began to get suspicious when a number of patients came in not just with gastrointestinal issues, but also with mental symptoms as well. “We don’t see brain fogginess, because we’re GI doctors,” Rao was quoted as saying.

Looking specifically at 30 patients with this combination of symptoms over the past three years, the research team found one major connection: All of them had reported taking probiotic supplements and, for some, eating probiotic yogurt. Meanwhile, in a control group of seven patients who had similar digestive issues but no brain fog, only one of them had reported taking probiotics.

To further test their theory, the researchers then gave the brain fog group antibiotics intended to wipe out some of these gut bacteria. Three months later, the 70 percent of the subjects suffering from brain fog said they felt much better, and 85 percent of that group said their brain fog symptoms were gone entirely.

Though this study certainly doesn’t mean that probiotics will cause brain fog for everyone—in fact, the study doesn’t even definitively show that probiotics were the cause of brain fog in the test subjects—researchers came to two important conclusions. First, doctors should be on the lookout for this set of symptoms to consider if probiotics might be the cause. And second, the study also states, “We advise caution against excessive and indiscriminate use of probiotics especially without a well-defined medical indication, and particularly in patients with gastrointestinal dysmotility, and/or those using long term PPI and opioids” who might be predisposed to this condition.

“I do believe they have beneficial effects…. I even use them in my practice as well,” Rao told Gizmodo. “I use them in very selective conditions, however—in people with dietary illnesses or who have taken antibiotics and had their balance of gut flora messed up. But this indiscriminate use of probiotics for any GI-related issue, I think, is a major problem.”

So, you know, maybe think twice before chasing those probiotic pills with an eighth container of probiotic yogurt.