The food you eat serves as fuel for your body. Food provides you with energy to keep your body processes running smoothly and allows you to get through the day. Three major nutrients, classified as macronutrients, supply your body with energy in the form of calories. Other nutrients, called vitamins, play important roles in converting food to energy.
Carbohydrates
Your body prefers carbohydrates as a primary source of energy. Carbohydrates contain calories, specifically 4 calories per gram, as well as glucose, a simple sugar. Your body obtains energy from both calories and glucose, making carbohydrates an energy powerhouse. When you eat carbohydrates, your body breaks them down into glucose. The glucose enters your bloodstream, where insulin picks it up and carries it to your cells for use as energy. Any extra glucose is converted to another substance, called glycogen, and stored in your liver. When you go for an extended period of time without eating, your liver releases glycogen for your body to use as energy. The only downside is that the ability to store carbohydrates is limited.
Fats
Fats are also a good source of energy. Of all the energy-yielding macronutrients, fat is the most energy dense, offering 9 calories per gram. In addition to its high calorie density, fat is a nutrient your body has an unlimited ability to store. When all of the glucose in the blood is used for energy and glycogen stores are depleted, the body begins to burn fat, which is stored in your fat cells as triglycerides, for energy. Because the body can store unlimited amounts of fat, these stores do not become depleted as glycogen stores do.
Protein
Protein also provides your body with energy. Like carbohydrates, protein contains 4 calories per gram. The body turns to protein only if it does not have access to carbohydrates or fat. Because protein plays a number of other important roles in the body, such as fluid balance, pH balance, immune system function and structural support to cells, the body prefers to use carbohydrates and fat for energy.
B Vitamins
The B vitamins, which include thiamin, riboflavin, niacin, folate, vitamin B6, vitamin B12, pantothenic acid and biotin, are also essential to providing your body with energy. While the B vitamins do not contain calories, they are a vital component in the chemical reactions that allow your body to metabolize carbohydrates, protein and fat. Without the B vitamins, you could not obtain energy from these macronutrients.
References
- Harvard School of Public Health: Carbohydrates
- "Nutrition and You"; Joan Salge Blake; 2008
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