MARATHON running may burn brain cells, according to a study.

Runners’ bodies digest fat when there are no carbs from food available.

But along with flab from belly and thighs, experts now reckon it may also be harvested from areas of the brain, potentially affecting its functions.

Post-marathon MRI scans of eight men and two women showed a reduction in myelin, a fatty covering which protects nerves and speeds up electrical signals.

Dr Carlos Matute, of Spain’s University of the Basque ­Country in Bilbao, said an “extensive” change was seen in areas linked to co-ordination, senses and emotions.

Follow-up scans showed normal levels again two months later.

Dr Matute believes myelin may help fuel the brain when energy stocks are low.

He said: “Our findings show that running a marathon reduces runners’ myelin water levels in white matter areas.

“This may open up a new view of myelin as an energy store ready to use when ­common brain nutrients are in short supply.”

He added: “It would be important to evaluate whether these changes affect brain functions.”

A world record 56,000 runners have signed up for next month’s London Marathon.

Longer endurance feats have also become mainstream, with reality TV star Jamie Laing running 150 miles in five days last week for Comic Relief.