What Are the Functions of Carbohydrates & Protein?

Carbohydrates and protein belong to a class of nutrients called macronutrients, which are named for the fact that you need large amounts of them in your body 1. Each macronutrient ensures that your body is able to carry out different, important functions. To keep your body functioning properly, it is important to consume adequate amounts of carbohydrates and protein 1.

Function of Carbohydrates

The main function of carbohydrates is to provide energy for the body, especially the brain and the nervous system 1. When you eat carbohydrates, an enzyme called amylase breaks them down into a simple sugar called glucose 1. The pancreas releases a hormone called insulin, which attaches to glucose and brings it to your cells so they can use it for energy. Insulin brings excess glucose to your liver, where it is converted to glycogen and stored for use when your dietary intake of carbohydrates falls short 1. When you go for an extended period without eating carbohydrates, another pancreatic hormone called glucagon converts glycogen back to glucose so you can use it for energy 1.

Function of Fiber

Fiber, a specific type of carbohydrate, has various functions and health benefits. Fiber can prevent and treat constipation and can lower your risk of developing diverticulitis, a digestive disease. Fiber in your digestive tract pulls water into your intestines, softening your stool and adding bulk to it. This makes the stool easier to pass and can reduce straining associated with passing a hard stool. Fiber also decreases the absorption rate of sugar in your intestines, which can control your blood sugar levels and decrease your risk of developing type 2 diabetes. Fiber also slows down digestion, which makes you stay full longer and can help you maintain your weight.

Functions of Protein

Protein provides your body with the structural support that allows you to move and bend. The most abundant protein in your body, collagen, keeps your blood vessels, bones and skin healthy. Protein also allows your body to synthesize various enzymes and hormones and helps your body maintain fluid balance and acid-base balance. Proteins can also act as transportation mechanisms, carrying oxygen, lipids, vitamins, electrolytes and waste products through your blood. Proteins can provide your body with energy if your intake of carbohydrates falls short, but “Nutrition and You,” by Joan Salge Blake, notes that you should not rely on proteins for energy because carbohydrates and fats are more suitable for this role 13.


Recommendations for carbohydrates and protein depend on your calorie intake 1. Carbohydrates should comprise 45 to 65 percent of your daily calorie intake, whereas protein should comprise 10 to 35 percent of calories 1. Carbohydrates and protein each provide 4 calories per gram, so if you consume 2,000 calories per day, your carbohydrate intake should be 225 to 325 g, and protein intake should be 50 to 175 g 1.