In a study conducted by researchers, the blood of obese mice had especially high levels of a chemical called interleukin 1, a substance born from fat cells that can cause inflammation. When researchers later examined the obese mice brains, they found that interleukin 1 had passed the blood-brain barrier, something that should not be possible.
The substance had seeped into the hippocampus, an area responsible for memory and learning. The mouse brains also had high levels of inflammation and low levels of a biochemical important to synapse function (synapses ensure messages travel efficiently between neurons).
These findings led to predictable results in how the mouse brains worked: Other obese mice did poorly on mouse-sized cognitive tests, presumably because the interleukin 1 was clogging things up.
But the study didn’t end there. The researchers wanted to make sure that it was the extra fat cells–and not something else, causing the disturbing brain changes in the mice.
Upon removing fat from the obese mice in a mini-liposuction procedure, the critters scored highly on the same thinking and memory tests they struggled with previously, and the interleukin 1 virtually disappeared from their bloodstreams.
When the researchers put fat pads inside thin mice, those previously svelte rodents started doing worse than they had previously on cognitive tests.