Too much fast food and too little exercise can harm the liver in just one month, research suggests.

A small study found that people who ate junk food twice a day experienced varying degrees of damage to their liver.

They also put on large amounts of weight in a relatively short amount of time.

Twelve men and six women – 17 of whom were students – were recruited for the study, published online in the journal Gut.

They were all healthy and slim, but for the study they ate at least two fast food meals a day, preferably from well-known fast food restaurants.

Exercise was also restricted to under 5,000 steps per day each.

Blood samples were taken at the start of the study, two weeks into the study and after four weeks.

Participants were urged to greatly increase their daily calorie intake, and only stopped the trial early if they gained 15% in weight.

Another group ate a normal healthy diet and acted as controls.