At the most basic level, nutrition is about eating a regular, balanced diet. Good nutrition helps fuel your body. The foods you eat supply the nutrients your body needs to maintain your brain, muscle, bone, nerves, skin, blood circulation, and immune system. Proper nutrition also helps protect you from illness and disease, such as heart disease, diabetes, cancer, and osteoporosis. There are two major classes of nutrients in food: macronutrients and micronutrients. Macronutrients are carbohydrates, protein, and fat. They supply energy (in the form of calories) and serve as the building blocks for muscles and tissues. In comparison, micronutrients are individual vitamins and minerals. They are divided into four categories: water-soluble vitamins, fat-soluble vitamins, microminerals, and trace minerals.