Obesity may have harmful effects on the brain, and exercise may counteract many of those negative effects, according to sophisticated new neurological experiments with mice, even when the animals do not lose much weight. While itís impossible to know if human brains respond in precisely the same way to fat and physical activity, the findings offer one more reason to get out and exercise.
Itís been known for some time that obesity can alter cognition in animals. Past experiments with lab rodents, for instance, have shown that obese animals display poor memory and learning skills compared to their normal-weight peers. They donít recognise familiar objects or recall the location of the exit in mazes that theyíve negotiated multiple times.
But scientists hadnít 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.
The consequences of that seepage became the subject of new neurological experiments conducted by researchers at Georgia Regents University in Augusta and published last month in The Journal of Neuroscience. For the studies, the scientists gathered mice bred to overeat and grow obese, which, after a few weeks of sitting quietly in their cages and eating at will, the animals had obligingly accomplished. As they grew rotund and accumulated more fat cells, the researchers found, their blood showed increasingly hefty doses of a substance called interleukin 1 that is created by fat cells and known to cause inflammation.
In these mice, as interleukin 1 migrated to the head, it passed the blood-brain barrier and entered areas such as the hippocampus, a part of the brain critical for learning and memory. There, it essentially gummed up the works, the researchers found when they examined tissue from the animalsí brains
But whether excessive fat cells alone were the underlying cause of the changes in the animalsí brains was not clear. Other