A Japanese airline is taking its weight-saving efforts to new heights, asking passengers on some of its flights to visit the restroom before flying.

The unusual request is one of a number of measures being tried out by All Nippon Airways to reduce fuel consumption.

ANA estimates that if half its passengers went to the bathroom before boarding, it could reduce its carbon dioxide emissions by 4.2 tons a month, said company spokeswoman Megumi Tezuka.

The airline will also recycle paper cups and plastic bottles, and use chopsticks produced from wood from forest thinning projects, as part of its efforts to become more environmentally friendly.

The measures are being trialled on 38 domestic flights and four international flights -- on the Tokyo-Singapore route -- during October.

The move follows earlier steps by airlines to reduce the weight of flights by trimming the size of in-flight magazines, slimming the handles of forks and spoons and using lighter drink trolleys and porcelain.

ANA announced in April its first annual loss in six years as the global economic downturn reduced the number of people taking to the skies.

It is not the only airline looking to the lavatory to save money. Irish budget airline Ryanair has previously said it is considering charging passengers to use on-board toilets.