White matter is the tissue that connects areas of the brain and allows for information to be communicated between regions.
Strikingly, however, the researchers only observed these differences from middle-age onwards, suggesting that our brains may be particularly vulnerable during this period of ageing.
"The fact that we only saw these differences from middle-age onwards raises the possibility that we may be particularly vulnerable at this age,” said senior author Professor Paul Fletcher from the Department of Psychiatry.
Our brains naturally shrink with age, but scientists are increasingly recognising that obesity - already linked to conditions such as diabetes, cancer and heart disease - may also affect the onset and progression of brain ageing.
In this study, the researchers investigated whether obesity was associated with brain changes characteristic of ageing.
The team studied data from 473 individuals between the ages of 20 and 87, recruited by the Cambridge Centre for Ageing and Neuroscience.
The researchers divided the data into two categories based on weight: lean and overweight.
They found striking differences in the volume of white matter in the brains of overweight individuals compared with those of their leaner counterparts.
Overweight individuals had a widespread reduction in white matter compared to lean people, showed the findings published in the journal Neurobiology of Aging.
The team then calculated how white matter volume related to age across the two groups.
They discovered that an overweight person at, say, 50 years old had a comparable white matter volume to a lean person aged 60 years, implying a difference in brain age of 10 years.
"It will also be important to find out whether these changes could be reversible with weight loss, which may well be the case," Fletcher said.