Use of probiotics linked to brain sluggishness and stomach bloating: Study

By Will Chu

- Last updated on GMT

The use of probiotics could lead to a build-up of bacteria in the gut causing brain fogginess, US researchers conclude, as they also note its use is linked to bloating of the stomach.

In the study, 79% of patients enrolled reported a number of symptoms after taking a variety of probiotics such as confusion, difficulty concentrating and bloating.

“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," ​said Dr Satish Rao, director of neurogastroenterology/motility at the Medical College of Georgia at Augusta University.

"Probiotics should be treated as a drug, not as a food supplement,"​ Dr Rao added noting that users often self-prescribe the live bacteria.

Probiotics are considered to be safe and beneficial including improvement in gut barrier function and gut transit. Lactobacillus​ species and bifidobacterium​ are the most common bacteria in probiotic formulations and are felt to be useful in the treatment of irritable bowel syndrome, inflammatory bowel disease, and other intestinal problems.

The study—published in the journal Clinical and Translational Gastroenterology​—appears to make a link to high levels of D-lactic acid in the gut and probiotic use with brain fogginess and bacterial overgrowth in the small intestine.

D-lactic acid is thought to be toxic to brain cells, affecting cognition, thinking and sense of time. From the study’s findings, Dr Rao and colleagues believe its production is caused by the bacteria lactobacillus​ and its fermentation of food sugars.

D-lactic acid then undergoes fermentation by lactobacillus and bifidobacterium in the bowel in a process known as D-lactic acidosis.

Recently, probiotic use has been implicated in the production of D-lactic acidosis, both in short bowel syndrome patients and in the first 2 weeks of life in infants who were fed probiotic-containing formula.

Study details

Dr Rao enrolled 38 patients, 30 of whom displayed signs of excess gas, bloating and brain fogginess (BF).

All patients in the BF group were taking probiotics over a period ranging from 3 months to 3 years.

Some of the patients were taking two or three different varieties containing lactobacillus ​species, and/or bifidobacterium​ or streptococcus thermophillus​ and others.

Additionally, 11 of these subjects (36.7%) were using cultured yogurt daily and two (6.7%) large amounts (20 oz.) of homemade cultured yogurt daily.

In 13 of the 30 subjects (43.3%) used multivitamins as well as fish oil and biotin supplementation in four of the 30 patients.

One patient in the group (3.3%) was taking ubiquinone, dessicated thyroid, simethicone, melatonin, curcumin, saw palmetto, samento extract, and artemisinin extract.

One patient (12%) in the non-BF group took probiotics (Lactobacillus rhamnosus​), whilst three out of the eight patients (37%) were using multivitamin and fish oil supplements.

All those with brain fogginess, small intestinal bacterial overgrowth (SIBO) and/or D-lactic acidosis, were given antibiotics that targeted their bacterial population and asked to discontinue probiotic use.

Those without SIBO were asked to halt probiotics and stop eating yogurt. Those with SIBO and D-lactic acidosis but no brain fogginess were also given antibiotics.

Following this course of treatment, 70% of patients reported significant improvement in their symptoms and 85% 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.

‘Probiotics definitely can help’

While the authors acknowledged the research's small sample size, Dr Rao added that “Probiotics are supposed to work in the colon and not the small intestines or stomach, so motility issues can result in problems with probiotic bacteria reaching the proper place”.​ 

“Conditions like diabetes to antidepressants drugs 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.

“Probiotics definitely can help, for example, people who have gastroenteritis, or stomach flu, or are left with diarrhoea and other problems after antibiotics wipe out their natural gut bacteria,”​ he added.

"In those situations, we want to build up their bacterial flora so probiotics are ideal."

Dr Will Bulsiewicz, a US–based gastroenterologist and gut-health expert added​ that, “Among thousands of patients seen over 3 years [Dr. Rao] has identified 30 that developed these symptoms. So this is an exceedingly rare finding,” he said.

The International Probiotics Association Europe, an industry group set up to serve the general interests of the European probiotic food industry, were unable to comment on the study's conclusions in time for publication.

Source: Clinical and Translational Gastroenterology

Published online ahead of print:

“Brain fogginess, gas and bloating: a link between SIBO, probiotics and metabolic acidosis.”

Authors: Satish Rao, Abdul Rehman, Siegfried Yu, Nicole Martinez de Andino

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1 comment


Posted by Anna Jacobs,

The discussion about brain fog and probiotics doesn't seem to have 'noticed' that there are other easily provable causes of brain fog. My brain fog used to be 90% the result of ingesting foods to which I'm mildly intolerant but didn't realise it. Also it can be caused by foods which I didn't know contained maize/corn under other names eg 'pre-gelatinised starch'. How is a simple person trying to eat mindfully to avoid triggers to foggy brain when one has to navigate such 'word fogging'?

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