Researchers at Cambridge University have found the brains of obese people age more rapidly than those of thinner people in middle age.
Human brains naturally shrink with age, but scientists are increasingly recognising that obesity may also affect brain ageing.
Researchers at Cambridge studied 473 people aged between 20 and 87, and found striking differences in the brain between obese and leaner people.
The academics discovered that an overweight person at 50 had the same white matter volume as a lean person 10 years older.
"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," Professor Paul Fletcher said.
"The fact that we only saw these differences from middle-age onwards raises the possibility that we may be particularly vulnerable at this age.
"It will also be important to find out whether these changes could be reversible with weight loss, which may well be the case."