How Fat May Hurt the Brain, and How Exercise May Help

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 it’s 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.
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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.

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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 animals’ brains, which had high levels of interleukin 1 together with widespread markers of inflammation. 

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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.

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