Once you get over the hill, obesity really starts to take a toll on brain function.

Researchers from the University of Cambridge were interested to see if obesity fast-tracked the brain shrinkage that naturally occurs with age. They went inside the heads of 473 adults aged 20 to 87 — some lean, some overweight — to look for any characteristic changes. And they found that leaner individuals in middle age had more white brain matter than those who were overweight. So an obese participant at age 50 looked to have the amount of white matter typically seen in someone 10 years their senior.

If there's an upside to this, it's that when researchers gave participants with lesser white matter a sort-of IQ test, it didn't seem to affect their overall cognitive ability, researchers said.

Going forward, older obese people should specifically be studied when it comes to obesity and premature aging of the brain, study co-author Paul Fletcher, a psychiatry professor at Cambridge, said in a press release. The findings made by Fletcher and his team suggests people are much more vulnerable in the middle stages of life.

“We're living in an ageing population, with increasing levels of obesity, so it's essential that we establish how these two factors might interact, since the consequences for health are potentially serious,” Fletcher said. It will be important to find out whether these changes could be reversible with weight loss, which may well be the case, he added.

What’s the big deal about losing white matter? For one, it’s considered “the subway of the brain;” it connects different brain regions together and helps keep an open line of communication between neurons that ultimately influence our behavior. When there are delays or lost signals, there's trouble (as any commuter can attest to). Studies have shown white matter deficits can lead to language, memory, and visual problems, as well as diseases like Alzheimer's, dementia, and depression.

Source: Ronan L et al. Obesity Associated With Increased Brain-Age From Mid-Life. Neurobiology of Aging. 2016.