We need energy
All living things need energy to grow and live.plants need light energy,water, and carbon dioxide to make food which they used to grow and produce fruits.Animal eat plants and other animals to gain energy.Like plants and animals human also need energy to remain alive , grow , to do all kinds of work, including walking, working,studying, driving a car etc. In short everything we do requires energy. We gain energy to do work from the food we eat.
Food provides us nutrients, which provide energy. The human body requires many nutrients including vitamins, proteins, carbohydrates, fats and minerals like calcium, iron, iodine, etc.