Japanese shoppers can now shed the pounds without counting the calories or working out down the gym after an apparel firm launched a new range of fat-burning underwear.

Boffins at Fuji Spinning Co claim to have designed a new lingerie line laced with caffeine and seaweed that eats fat when absorbed into the skin.

Their new "Wonder Slim" fabric contains caffeine and seaweed extracts which when dissolved into the skin combine with body oils and sweat to activate fat-eating enzymes.

The company says the extracts continue to be absorbed into the body after the undies have been washed many times, although it can't promote their fat-burning effects as they are not sold as a pharmaceutical item.

The underwear is targeted at both men and women and costs between $20 and $35 but will not be sold outside Japan.