The US commander in Afghanistan, General Stanley McChrystal, has banned American and NATO troops from eating fast food.

The general, who runs 13 kilometres every morning and eats just one meal a day, has ordered junk food outlets on all military bases to be closed.

Military leaders say the decision was made because Afghanistan is a war zone, not an amusement park.

The decision is not likely to be popular with those stationed on bases serviced by fast food outlets, but will free up supply lines for frontline soldiers in need of fresh food and running water.

"From the moment [General] McChrystal and I arrived in Afghanistan last summer, we began looking for ways to do things more efficiently across the battlefield," Sergeant-Major Michael Hall wrote in a military blog, quoted by the Times Online.

"This effort includes moving and reallocating resources to better accomplish our mission.

"Supplying non-essential luxuries to big bases like Bagram and Kandahar makes it harder to get essential items to combat outposts and forward operating bases, where troops who are in the fight each day need resupplying with ammunition, food and water."

Last year, General McChrystal banned alcohol at NATO's Kabul headquarters after complaining that too many staff were coming to work with a hangover.