because we need the energy stored in food, we need energy for survivng, otherwise we can't live or we get diseases.
因為我們需要食物裏的能量去繼續生存,否則我們就會死或者有生病的情況。所以我們需要它們啦。
since we need different nutrient and enough energy to maintain our life from eating .we feel hungry because it give signal to us to remind us to eat food.