Can gut bacteria tell if Alzheimer's is developing?

One of the most amazing features of the human body is the gut-brain axis.  As we discussed last summer, microorganisms in the intestines have a signaling network with the brain such that the microorganisms exercise a significant level of control over what happens in the brain.  Bizarre, I know.  Nevertheless, good gut health contributes to good neurologic health.

Doctors often refer to "gut flora," meaning gut plants.  This hearkens back to the 1950s, in my late elementary school days, when the biological sciences were trying hard to sort all life as either plant or animal.  And they were trying hard to force fit bacteria into the plant kingdom.  That didn't work out very well.  It turns out that bacteria are more different from plants than plants are from animals.

And so more sophisticated folks will refer to "gut bacteria."  But that's not quite right either.  Many of the microorganisms in your gut are archaea.  Archaea are often referred to as bacteria, partly because, like bacteria, their cells have no nuclei.  They are the organisms that can live under extreme conditions, such as near volcanic vents on the sea floor.  They stain the glaciers on Mount Rainier pink, they allow goats to digest cellulose, and they give the hot water pools in Yellowstone their beautiful colors.  But there are ways in which they are significantly more different from bacteria than plants are from animals.

So we will refer to the gut microbiome and skip worrying about whether their citizens are plants, animals, bacteria, or archaea.  

Now since the gut microbiome plays such an important role in how the brain functions, it may also play a role in how Alzheimer's disease develops.  Therefore, logic says that you should be able to see the development of Alzheimer's disease somehow reflected in the gut microbiome.  Can you?  Maybe so.  

There was a new study published in the June 14, 2023 edition of the journal Science Translational Medicine, "Gut microbiome composition may be an indicator of preclinical Alzheimer’s disease."  As indicated in the title, the research explored the idea that Alzheimer's disease might be detected by analyzing changes in the gut microbiome during the preclinical phase of the disease.  This is before any symptoms develop.

The researchers studied 164 cognitively normal people, 49 of whom had evidence of preclinical Alzheimer's disease.  In other words, the 49 passed cognitive tests OK, but they had other evidence that the disease had already begun.  As we said in Beating the Dementia Monster, the preclinical stage normally lasts about 15 years, only ending when the first symptoms appear.  Usually it is simply undetected during that stage. 

So what did the research find?  "The gut microbiomes of people with preclinical Alzheimer's disease (indicated by altered brain amyloid and tau proteins) had a different composition from that of healthy individuals."  This means that examining fecal matter may turn out to be a less invasive method for diagnosing Alzheimer's disease than, say, the spinal tap that I underwent. 

On the other hand, if the blood tests we've been anticipating turn out to be as reliable as they appear, they may end up being the preferred diagnostic tool.  The gut microbiome researchers compared their approach to the spinal tap rather than the blood test.

Aside from perhaps using changes in your gut microbiome to diagnose Alzheimer's disease, some believe that supporting good gut health supports good brain health.  That may or may not be true, but I still do things thought to support the gut microbiome.  I eat yogurt (without all the sugar), fermented foods like kimchi, and fiber supplements.

This idea of resisting Alzheimer's disease by caring for your gut underscores something we've said before: this is an incredibly complex disease, and we just don't understand it well at all.