An illustration of a brain floating in space.
gutPhoto by Milad Fakurian on Unsplash

Chemo Brain Fog: Blame it on the Gut Bugs?

Michael Hunter, MD
BeingWell
Published in
6 min readAug 5, 2024

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Earlier this week, I met a lovely young woman who had recently completed chemotherapy for breast cancer.

She complained of treatment-related cognitive impairment — chemo fog — with some memory and thinking problems.

As a radiation oncologist, I often hear cancer survivors use the term “chemo brain” to describe the frustrating cognitive difficulties they experience during and after treatment.

I sometimes hear such complaints after radiation therapy or pills (endocrine therapy) that block estrogen.

While “chemo brain” is a widely recognized term, the exact causes of these cognitive problems remain elusive.

Illustration of wires going into a translucent head/brain.

Now comes a possible explanation for chemotherapy-induced brain fog: the gut microbiome.

Let’s briefly examine chemobrain symptoms, risk factors, and new evidence pointing to the gut.

I’ll end with some tips about how you can optimize your microbiome.

Chemo Brain Symptoms

The manifestations of chemo brain can be diverse and often subtle, affecting various aspects of cognitive function.

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Michael Hunter, MD
BeingWell

I have degrees from Harvard, Yale, and Penn. I am a radiation oncologist in the Seattle area. You may find me regularly posting at www.newcancerinfo.com