Nutrition is the platform of eating for health vs fueling which occurs during exercise to make forward process. When it comes to nutrition you are your metabolism which is the totality of all the chemical actions and interactions that are constantly occurring in your body. There are two sides to this process, building and using; fight or flight and rest and digest. In order to stay healthy, you must replace or restore what you have used moving through your day and/or exercise. If not, you break down inviting injuries, illness and potentially disease.
There are four macronutrients; referred to as macros: carbohydrates (carbs), protein, fat and water. Carbs provide us with energy and is the only nutrients our brains use. We store about 90 minutes worth of activity in our muscles and liver. They provide 4 calories per gram and should make up 40 to 65% of your daily calorie intake. Carbs break down very quickly, starting in your mouth which is why they are the best energy source. They can be complex or simple, nutritious to nutrient void, potatoes to candy and they all break down into glucose.
Protein provide us with the building blocks to repair and heal, it's part of the rebuild process. It can provide energy when carbs are not present or are low but it takes 2+ hours to digest so it is not efficient. We don't store protein other than as muscle mass so if we rely on it for energy we will break down muscle tissues; not good. They also provide us with 4 calories per gram and should make up 15 to 30% of your daily intake. Protein is anything from beef, chicken, fish to eggs, peanut butter or gelatin.
Fat provides energy but only when oxygen is present (moderate intensity), it also helps hormones move around the body and improves our immune status. It provides 9 calories per gram, takes a long time to break down and should make up 15-30% of our daily consumption.
Water provides lubrication, it is used in all its cells, organs, and tissues to help regulate its temperature and maintain other bodily functions. You loses water through breathing, sweating, and digestion so it must be replaced at half of your body weight in ounces. (ex: 150 pounds, drink 75 ounces.)
FYI: Alcohol provides 7 calories per gram and zero nutrition.