Every atom, every molecule, every cell, tissue, organ, and system in your body is made up of the ingredients in the foods you eat, the water you drink, and the air you breathe. Cell membranes are made up of fats and proteins from foods like the salmon or nuts you had for lunch. The iron in your red blood cells that carries oxygen to your brain and tissues came from something as simple as the black beans in a burrito. The energy your brain uses to relay messages comes from the carbs in a bowl of cereal at breakfast, and the B vitamins that convert those carbs into cell energy came from the milk you poured over the cereal. So, it just makes sense that you literally are exactly what you choose to eat.