As hair is primarily made up of protein, you can understand the importance of consuming protein rich foods in making hair grow fast naturally.
Some such protein rich foods for hair growth are:
Soy products, Beans (try chickpeas or lima beans), Eggs, fish (salmon), milk (soy milk), cheese, yogurt, whole grains, seeds and nuts.
Adding herbs such as parsley, oregano, cumin seeds, coriander leaves, basil, sage etc is also beneficial for hair.
Dark green vegetables such as Swiss chard and kale are rich sources of iron that assists in hair growth by carrying oxygen to hair.