Since you will get hurt a lot, even on easy, this achievement will come naturally as you progress. Instead of eating any food stuffs to replenish your health, use the health potions (the red bottles) to heal yourself. It doesn't matter what size they are, as long as you drink 50 of them. If you can't find enough through exploring the world, you can buy them at the General Store in Pluckmuckel, which is the first major town you go to. It's to the north of your starting location and you reach it after the Demon Mines.