Excessive intake of probiotics can lead to brain fog, suggesting that high-dose supplementation is not necessarily better for health.

“there are studies that show that if you take lots and lots of certain probiotics, like lactobacillus, and you really ramp up the levels more, it is not a case of more is better. There are things like brain fog that can come from that. Brain fog is just this inability to focus.”

The gut-brain axis is a two-way communication system where the brain monitors internal state and modulates physiology based on nutrient sensing.

“monitoring of the brain has been known for a long time, but I think what hadn't been fully appreciated that this is a two-way highway where the brain is not only monitoring, but is now modulating back what the body needs to do.”