Gut and Brain Redux

Perhaps there's a love-hate relationship between your gut and your brain.  On the one hand, it appears that microbes in your gut are controlling much of what goes on in your brain in mysterious ways.  That's called the gut-brain axis.  But at the same time, your "leaky gut" is killing your brain.  With respect to the latter, we've known for a long time that, as we age, the walls of the intestines are less able to contain the gut bacteria.  The bacteria leak out into the abdominal cavity and create inflammation throughout the body, including in the brain.  Much of our battle against Alzheimer's disease is to control inflammation, and gut bacteria becomes a major adversary.

How the gut bacteria makes its way to the brain is coming into sharper focus, and there's better information on how to put the brakes on that process.  (Spoiler alert:  It's a high fiber diet.)  My friend Teale sent me this article from Neuroscience News about new research findings on leaky gut and brain inflammation.  The researchers at the LSU Health New Orleans Neuroscience Center and the Departments of Cell Biology and Anatomy, Neurology, and Ophthalmology examined the culprit bacteria, Bacteroides fragilis.  This bacteria generates a neurotoxin known as BF-LPS.  At autopsy, it's found in the brain cells of Alzheimer's patients.  

How BF-LPS is able to cross the blood-brain barrier is not clear to me.  Perhaps it's a relatively small molecule, allowing it to cross both the intestinal membranes and the blood-brain barrier.  Recall that the blood-brain barrier allows smaller molecules to pass but screens out larger molecules and microbes.  But the intestinal membranes and the blood-brain barrier both weaken as we age.

When the BF-LPS reaches the brain, it not only causes inflammation, but it also inhibits the action of a protein called NF-L.  NF-L is important to the survival of neurons, and when its actions are inhibited like this, brain cells die, and the brain atrophies.  

So what can we do about this?  Control Bacteroides fragilis, so that it can't generate BF-LPS.  The design of your gut is such that it expects a certain fraction of what you eat to be dietary fiber.  I'd describe the situation like this.  If you're not eating enough fiber, your gut bacteria becomes unbalanced, and Bacteroides fragilis will generate a lot more BF-LPS.  So make sure you have a high-fiber diet.

How much fiber?  The USDA recommends that women up to age 50 consume 25 grams a day and men 38 grams.  Women and men over age 50 should consume 21 and 30 grams daily, respectively.  A medium-sized apple contains about 4.4 grams of fiber.