Koalas eat only the leaves of a few kinds of gum trees.Theyalso need to choose fresh leaves because the older leaves contain poisons.Koalas spend three-quarters of their lives asplle because their food provides very little energy. Koalas eat only the leaves of a few kinds of gum trees.Theyalso need to choose fresh leaves because the older leaves contain poisons.Koalas spend three-quarters of their lives asplle because their food provides very little energy.