Probiotics Not Cause of Brain Fogginess

By Anthony Thomas, Ph.D.

In a recently published research manuscript [1], Rao and his colleagues blamed use of probiotics for causing symptoms of “brain fogginess” secondary to their promotion of small intestinal bacterial overgrow (SIBO) and elevated levels of D-lactic acid in the blood of patients with reportedly normal digestive functions.  Their provocative conclusions were quickly covered and propagated by multiple media outlets including Newsweek, Science Daily, and Psychology Today, without a critical review of the evidence claimed to support these assertions.

Many scientists with genuine expertise in probiotics outright rejected the conclusions promoted by Rao and his colleagues due to critical flaws in their study, a glaring lack of evidence to support their conclusions, and their misrepresentation of probiotic bacteria as well as research cited in an effort to support their otherwise scientifically unsupported conclusions.  Despite the safe use of probiotics by millions of people the world over, the irresponsible media coverage of this research publication casts doubts as to the safety of probiotics and strongly suggests high potential for harmful health effects with their use.   

The scientific journal this research was published in, Clinical and Translational Gastroenterology, has now published a critical response from probiotic scientists that rebuts the conclusions of Rao and his colleagues that highlights some of the primary flaws of the research as well as the researchers’ misrepresentations of probiotic bacteria and cited scientific evidence leveraged to support their empirically unfounded conclusions [2].


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  1. Rao S, Rehman A, Yu S, Andino N: Brain fogginess, gas and bloating: a link between SIBO, probiotics and metabolic acidosis. Clin Transl Gastroenterol 2018, 9:162.
  2. Quigley E, Pot B, Sanders M: ‘Brain Fogginess’ and D-Lactic Acidosis: Probiotics Are Not the Cause. Clin Transl Gastroenterol 2018, 9:187.