If you think of energy as calories, it’s pretty clear that your body can pull energy from all the different foods you eat each day. Whenever you eat something, your body begins to break down the nutrients contained in each bite to use them in various bodily functions. While carbohydrates are your body's main source of energy, proteins and fats can also be sources of energy.
Carbohydrates are your body's preferred source of energy. In fact, your body turns all the carbs you eat into glucose, which provides a quick energy supply. Your body can also store carbs in your liver and muscles as glycogen, which it can use later for energy when you need it. The carbohydrates you don’t need right away and that can’t be stored in the liver, though, turn to fat.
Your body uses fats to produce more than half its energy needs. In fact, fats provide more energy than carbs, gram for gram. But don’t get carried away – the body converts only about 10 percent of fat into glucose for immediate energy use. The fatty acids that are formed from the fats you eat are stored in fat cells as triglycerides. Those fat cells have unlimited capacities. While stored fat can be used later when the body runs low on carbohydrates, it will take a while to use up the stored carbohydrates to necessitate the use of stored fat as energy.
Your body will use proteins for energy only if it’s missing the other two nutrients. That’s because protein’s primary role is to build muscle, repair cells and create new ones, and distribute the nutrients you take in throughout the body. Proteins are formed by long strands of different amino acids. If the proteins aren’t needed for their primary purpose, these amino acids can break apart from the group and be oxidized to provide energy.
For your body to function properly and for you to get the energy you need, you need to eat a balanced healthy diet containing all three nutrients. You should get most of your daily calories – 45 to 65 percent – through healthy carbohydrates, from foods such as whole grains, brown rice and fruits and vegetables. Proteins should make up about 10 to 35 percent of your daily calories. MayoClinic.com stresses the consumption of plant-based protein, like beans and soy-based products, and low-fat poultry and meat. You should limit fats to 20 to 35 percent of your daily calories, with an emphasis on unsaturated fats from healthy oils and lean meats.
Lucy D'Berry has been a writer for nearly 30 years, specializing in nutrition and health issues, as well as in education and government. She has written for daily newspapers and edits a national magazine. She has earned both a bachelor's degree and a master's degree in the communications field.