When weatherman Al Roker hit 340 pounds, he knew he needed to change his ways. Bariatric surgery in 2002 launched him on a journey that, with ups and downs, helped him cruise into his 60s as a much healthier 190-pound man.

How did he change his relationship to food? One bite at a time.

For example, he says, “I try not to read and eat. And interestingly, since I stopped that habit, my comprehension is even better.”

That wouldn't surprise researchers who recently discovered that a healthy weight and smaller waist size mean a more robust brain, and that a higher body mass index (BMI) and larger waist is associated with a thinning cerebral cortex — where thinking, seeing, and talking go on.

The six-year study published in the journal Neurology looked at almost 1,300 people with an average age of 64. Participants who were obese (BMI of 30+) had an average waist circumference of 41 inches; those at a healthy weight (BMI of 18.5 to 24.9) averaged a 33-inch waist.

MRI scans of their brains revealed that every unit increase in BMI was associated with a measurable decrease in the thickness of the brain cortex.

For obese people, the thinning was pretty dramatic — especially in those younger than 65. Their brain aging was accelerated by at least a decade.

So to stay smart and aim for a healthy weight. Ditch highly processed foods and red meat, and get 150 to 300 minutes of aerobic exercise a week, plus two 30-minute strength-building sessions weekly.