There are three different macronutrients: 

•    Carbohydrates

Carbohydrates are your body’s main source of energy. They fuel your brain, muscles and nervous system, making them especially important if you are active. 

Carbohydrates provide 4 kcal per gram. 

•    Protein 

Protein helps build, repair and maintain tissues throughout your body. It’s needed for healthy muscles, bones, skin, hormones, enzymes and your immune system. 

Protein also provides 4 kcal per gram. 

•    Fat 

Fat often gets a bad reputation, but it is essential for good health. Your body needs healthy fats to produce hormones, protect your organs, absorb certain vitamins and support brain function. 

Fat provides 9 kcal per gram, making it the most energy-dense macronutrient. 

How are calories and macronutrients related?

Calories are a measure of the energy your body gets from food, which it uses to fuel everything from breathing to exercise and tissue repair. Those calories come from three macronutrients: carbohydrates, protein and fat. 

Think of calories as the fuel in your car, and macronutrients as the type of fuel you are putting in. While the amount of fuel matters, so too does the quality. For example, a grilled chicken breast and a small slice of cake may contain a similar number of calories, but they affect your body very differently. Chicken is rich in protein that helps build and repair muscle, while cake contains more sugar and fat and provides far less protein. 

References

1. Institute of Medicine. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fatty Acids, Cholesterol, Protein and Amino Acids. National Academies Press; 2005.
2. World Health Organization, Food and Agriculture Organization of the United Nations, & United Nations University. Protein and Amino Acid Requirements in Human Nutrition. WHO Technical Report Series 935. Geneva: WHO; 2007.
3. International Society of Sports Nutrition. Jager R, Kerksick CM, Campbell BI, et al. International Society of Sports Nutrition Position Stand: Protein and Exercise. Journal of the International Society of Sports Nutrition. 2017;14:20.
4. Morton RW, Murphy KT, McKellar SR, et al. A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength. British Journal of Sports Medicine. 2018;52(6):376-384.
5. Bauer J, Biolo G, Cederholm T, et al. Evidence-based recommendations for optimal dietary protein intake in older people: A position papers from the PROT-AGE Study Group. Journal of the American Medical Directors Association. 2013;14(8):542-559.
6. Academy of Nutrition and Dietetics. Raj S, Guest NS, Landry MJ, et al. Vegetarian Dietary Patterns for Adults: A Position Papers of the Academy of Nutrition and Dietetics. Journal of the Academy of Nutrition and Dietetics. 2025;125(6):831-846.e2.