Energy substrates are the molecules that provide energy for biological processes in living organisms. The primary energy substrates include carbohydrates, fats, and proteins. When these substrates are broken down through metabolic pathways, they release energy that cells use for various functions, such as growth, repair, and movement. Carbohydrates, like glucose, are often the first source of energy because they can be quickly converted into usable energy. Fats provide a more concentrated energy source and are utilized during prolonged activities. Proteins can also serve as energy substrates, but they are primarily used for building and repairing tissues rather than as a primary energy source.