Gorging on probiotics for good health? It may cause brain fogginess and belly bloating

WASHINGTON: Consuming too much of probiotics can cause brain fogginess and disorientation, as well as rapid belly bloating, according to scientists - including one of Indian origin - who advise people against self-prescribing 'good' bacteria. In a study of 30 patients, researchers found that 22 who reported problems like confusion and difficulty concentrating, in addition to their gas and bloating, were all taking probiotics, some several varieties.

When the researchers 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 bacteria lactobacillus' fermentation of sugars in their food, said Satish S C Rao, from Augusta University in the US.

While probiotics can be beneficial in some scenarios, like helping a patient restore his gut bacteria after taking antibiotics, researchers 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 considered good for digestion and overall health.


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 study, 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.

"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 colonise your small bowel with probiotic bacteria, then you have set the stage for potentially developing lactic acidosis and brain fogginess," Rao said.

Others have implicated probiotics in the production of D-lactic acid - and brain fogginess - in patients with a short bowel so their small intestine does not function properly, and in newborns fed formula containing the popular product.


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.

All patients experiencing brain fogginess took probiotics and SIBO was more common in the brain fogginess group as well, 68 per cent compared to 28 per cent, respectively.

Patients with brain fogginess also had a higher prevalence of D-lactic acidosis, 77 versus 25 per cent, respectively.

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.

Good food sources of probiotics include yogurt, sauerkraut, kimchi, kefir and dark chocolate, which are generally safe because of the small amounts of bacteria present, Rao said.