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

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

Runners at the start of a marathon.Marathon running may burn brain cells, according to a study

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 .