Can SIBO Cause Brain Fog?

Have you been feeling a bit slow recently? You’re unable to recall things or process information as easily as you used to. Or maybe you’re unable to speak properly or focus on a task for long. If all of this happens after you eat a meal, you might have something called SIBO brain fog.

What is SIBO brain fog? Read on to find more about what SIBO is, how it can lead to brain fog, and other potential causes of brain fog.

What is SIBO?

SIBO stands for small intestinal bacterial overgrowth. Unlike the large intestine, the small intestine is free of bacteria in healthy individuals. This is due to stomach acid and bile, both of which wash down the small intestine and are harmful to bacteria.

In SIBO, bacteria found in the large intestine can creep up and make their way to the small intestine. Once they reach there, they can begin dividing and develop into a large colony of bacteria, which causes the symptoms of SIBO.

As these bacteria ferment molecules found in the diet and release chemical byproducts, patients with SIBO develop:

● Diarrhea
● Steatorrhea — fatty, foul-smelling diarrhea that’s difficult to flush. This occurs due to a decrease in fat absorption.
● Weight loss
● Deficiencies of vitamins A, D, E, K, and B12
● Zinc and iron deficiency

There are a wide range of causes behind SIBO. Anything that prevents the washout of acid and bile through the small intestine will cause bacterial overgrowth. For example, conditions like scleroderma, diabetes mellitus, and irritable bowel syndrome (IBS) can all impair the motility of small intestines, leading to bacterial overgrowth.

Certain anatomic (or physical) causes for SIBO exist too. These include:

● Inflammatory bowel disease — this includes Crohn’s disease and ulcerative colitis
● Blind loop syndrome, where bacteria proliferate in a blind intestinal loop that results from a surgical procedure
● Small bowel diverticulosis, where multiple outpouchings of gut form in the small intestine and bacteria can grow inside these pockets

If you have any of these conditions and have now developed brain fog — and experience symptoms after eating a meal — you may have SIBO. How does SIBO cause brain fog? Let’s find out.


Can SIBO cause brain fog?

Yes, SIBO can lead to brain fog, especially after you consume a meal.

As you eat food, it’s fermented by bacteria in the small intestine. These bacteria produce a molecule called D-lactic acid during fermentation, which has harmful effects on body cells.

L-lactic acid is naturally produced in the body as a result of various chemical processes. It’s levels are especially increased after strenuous exercise but unlike D-lactic acid, it’s not as harmful for body cells.

D-lactic acid impairs the ability of cells to create energy (ATP molecules) via various processes like oxidative phosphorylation. As a result, cells with a high demand of energy (cardiac and brain cells) suffer the most.

In the brain, impaired energy synthesis hampers various housekeeping functions like neurotransmitter turnover and nerve impulse generation. The result? Brain fog.

Histamine, which is another molecule produced by bacterial metabolism, can also lead to brain fog in patients with SIBO.

How to get rid of SIBO brain fog?

Since the main culprits behind SIBO brain fog are the harmful substances that bacteria produce, treating SIBO to get rid of those bacteria should also treat your brain fog.

If you have any of the conditions described above and suspect you might have SIBO, the first thing you should do is consult a doctor.

Diagnosis of SIBO begins by a medical history and examination, where the doctor asks about your symptoms, their severity, duration, and progression. Physical examination involves palpating your abdomen and listening to gut sounds using a stethoscope.

If your symptoms point towards SIBO, the doctor may order a lactulose breath test. During a breath test, you’re required to drink a lactulose-containing drink and then breathe into a tube. If there’s bacterial overgrowth, bacteria will consume lactulose and release hydrogen gas. This gas is detected as you breathe into a tube.

If breath test results aren’t clear, you may be required to undergo a jejunal aspiration procedure, where a small sample of fluid is collected from the small intestine to detect the bacteria growing there.

Once the diagnosis of SIBO is established, you can begin therapy to eliminate bacteria from the small intestine. This can be achieved using various antibiotics such as metronidazole, ciprofloxacin, or rifaximin. These drugs are prescribed based on your overall health conditions and any other medications you’re taking, so self-medication is never a good idea.

As antibiotics begin to eradicate bacteria in your small intestine, you may see an improvement in your brain fog.

An elemental diet is also very effective at treating SIBO. This is where you replace your normal diet with liquid formulas for a specific period. You must discuss this option with your doctor before starting it.

Finally, probiotics are also an option for treating SIBO but the scientific evidence for their effectiveness is mixed. It’s best to discuss them with your doctor.

Other potential causes of brain fog

Several other causes of brain fog exist as well. It’s a good idea to be aware of them because if your brain fog is not related to dietary patterns, you may be suffering from one of the following:

● Hormonal changes — changing levels of estrogen and progesterone during pregnancy or menopause can lead to cognitive impairment
● Sleep deprivation
● Long-term stress
● Food allergies — common culprits are sweeteners like aspartame, dairy, peanuts, and monosodium glutamate
● Side effects from medications
● Fibromyalgia
● Chronic fatigue syndrome
● A wide range of medical conditions like anemia, hypothyroidism, and depression

Since there are many possible causes of brain fog, it’s best to get yourself evaluated by a doctor instead of simply attributing it to diet and SIBO.


Can SIBO cause brain fog? Yes. Bacteria in the small intestine produce substances like D-lactic acid and histamine, which interfere with normal brain metabolism and may lead to brain fog.

If you suspect you have SIBO, you can undergo a lactulose breath test to get a formal diagnosis. Treatment with antibiotics can then eradicate the bacteria in your small intestine, improving your brain fog.

Medically Reviewed by Onikepe Adegbola, MD PhD

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