Researchers have found evidence that the brains of middle-aged, overweight people have the same amount of white matter - the connective tissue that allows the brain to communicate - as a lean person 10 years older.

If confirmed, the results suggest that obesity could play a role in how fast a person's brain ages, causing it to shrink faster than a lean person's would.

"As our brains age, they naturally shrink in size, but it isn't clear why people who are overweight have a greater reduction in the amount of white matter," said one of the team, Lisa Ronan from the University of Cambridge in the UK. "We can only speculate on whether obesity might in some way cause these changes or whether obesity is a consequence of brain changes."

The team examined the amount of white matter in 527 individuals between the ages of 20 and 87. They divided this data into groups depending on if the person was lean or overweight, based on their BMIs.

Comparing the amount of white matter for each group, the researchers found that the brains of the overweight individuals were roughly 10 years older than their lean counterparts. In other words, a 50-year-old overweight person had the same amount of white matter as a 60-year-old lean person.

The good news is that despite the drop in white matter, the researchers didn't find any signs of cognitive decline in the overweight group, which they analysed using a standard IQ test.

They also mention that the drop in white matter only occurred in middle-aged individuals - not younger - but they don't yet understand why.

"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," said one of the team Paul Fletcher.

"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."

The results will need to be backed up by additional studies before we can figure out how obesity might be linked to the reduction of white matter in middle-aged brains, and there are some serious problems with BMI that could skew them slightly.

But this isn't the only study that reveals how lifestyle choices might have a negative impact on our brains after a certain age. Last month, an international team of researchers found that the typical 40-hour work week could cause cognitive decline in people over 40-years-old.

Interestingly, they also found that working less than 25 hours had a similarly negative mental impact, suggesting that each person has a 'sweet spot' between 25 and 30 hours where cognition is best.

Hopefully, as scanning technology gets more advanced, researchers will one day be able to understand how lifestyle affects our brains on both a cognitive and physical level.

The findings have been published in the journal Neurobiology of Aging.