After analyzing imaging from 527 adults, the researchers discovered overweight people—those with a body mass index (BMI) over 25—had lower volumes of white matter in their brains than people with a BMI of under 25 did.
White matter is the tissue that connects different areas of your brain with each other and allows for communication between your neural regions. It helps you with everything from memory to thinking quickly.
In fact, overweight subjects had brains similar to healthy-weight people who were 10 years older."
Huh. Imagine that, being overweight ages your brain by 10 years. Luckily, it doesn't make you any stupider.