This is a long, complicated story but it’s a tour-de-force of scientific investigation. In mice, but may apply to people. Of course, memory loss and dementia have huge Macroeconomic impact.
In a nutshell:
We all (mice and humans) have a huge variety of microbes living in our gut – the microbiome. Many are friendly (digesting our food, producing anti-inflammatory molecules, etc.) but others are not so friendly.
Parabacteroides goldsteinii, a bacterium common in older animals, was linked to memory loss. This is true in younger animals as well as older and it’s reversible. P. goldsteinii produces chemicals (medium chain fatty acids or MCFAs) that irritate the immune system and cause inflammation.
The inflammation dampens activity along the vagus nerve, a bundle of neurons that communicates sensations such as stomach fullness to the brain. These animals also showed reduced activity in the hippocampus, a brain region associated with learning and memory.
There’s a lot of back-and-forth communication between the brain and gut via the vagus nerve. I read a book about this a few weeks ago. Could lack of stimulation via the vagus nerve cause the hippocampus to atrophy? It wouldn’t be surprising.
How does this tie into junk food? It’s biochemistry.
While the body can produce some MCFAs, the majority come from specific dietary fats or microbial fermentation of certain precursors.
The most direct way to reduce MCFA levels in the gut is to limit fats that are naturally composed of 60–90% MCFAs. Coconut Oil and Palm Kernel Oil are often found in processed snacks, non-dairy creamers, and “hydrogenated” vegetable oils.
Anyone can avoid these by using olive oil instead of high MCFA fats.
The study is very detailed and opens the possibility that memory loss could be treated via the bacteria/ immune inflammation/ vagus nerve pathway that wasn’t on anyone’s radar screen until now.
https://www.nature.com/articles/d41586-026-00768-6
Wendy