...But scientists hadn’t understood how excess weight affects the brain. Fat cells, they knew, manufacture
and release substances into the bloodstream that flow to other parts of the body, including the heart and muscles. There, these substances jump-start biochemical processes that produce severe inflammation and other conditions that can lead to poor health.
Many thought the brain, though, should be insulated from those harmful effects. It contains no fat cells and sits behind the protective blood-brain barrier that usually blocks the entry of undesirable molecules.
However, recent disquieting studies in animals indicate that obesity weakens that barrier, leaving it leaky and permeable. In obese animals, substances released by fat cells can ooze past the barrier and into the brain.
...
So the scientists turned, as a less-invasive alternative, to exercise. Gathering more of the obesity-prone mice, they allowed all of them to grow heavy, but then started half on a daily 45-minute program of treadmill running, with encouragement provided by small puffs of air if they began to flag. The other mice remained sedentary.
After 12 weeks, the running mice still weighed about the same as the unexercised animals. But they had lost significant amounts of fat from around their middles, while adding lean muscle. More telling, they did much better on cognitive tests than the sedentary mice and, when the researchers examined tissue from their hippocampi, showed little evidence of inflammation and robust levels of the chemical marker of synaptic health. The results suggested that, as the scientists write in the study, “treadmill training normalized hippocampal function,” even in animals born to be fat and that remained heavy.
http://well.blogs.nytimes.com/2014/03/05/how-fat-may-harm-the-brain-and-how-exercise-may-help/
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