For those in middle age, the secret to whether we will suffer from Alzheimer’s disease may be hiding in our girth.

Researchers have linked a type of body fat to unwanted proteins in the brain that are known to appear as long as 20 years before Alzheimer’s does.

The Washington University research team wanted to look at how Alzheimer’s begins in its earliest stages, when people are in their 40s and 50s.

Close to 7 million Americans ages 65 and older now have the disease. The Alzheimer’s Association estimates that without a medical breakthrough, the number could nearly double by 2050.

The scientists said that lifestyle modifications aimed at reducing extra pounds in the belly could stem the tide. In Alzheimer’s, brain cells and their connections degenerate and die. It leaves sufferers without memory and in cognitive decline.

The researchers homed in on the links between Alzheimer’s progression and changeable lifestyle factors, such as obesity, body fat distribution, and metabolics.

A pool of 80 people, who on average were 49 years old, were studied … more than half of them women. About 57% of participants were obese.

Participants’ brains were scanned, their glucose, insulin and cholesterol measured. Their bellies were evaluated for the type of fat found just under the skin as well as visceral fat, the kind that tucks itself in around internal organs.

Their findings: Higher levels of deep belly fat are related to increased amyloid and tau, Alzheimer’s signature proteins.

With 3 of 4 Americans overweight or obese, doctors say it’s important to help people find ways to lose weight and control cholesterol, whether it’s with medication or plain old diet and exercise.