Macronutrients
Also known as: macros
Macronutrients are the three nutrients the body needs in large amounts and can use for energy: carbohydrates, protein, and fat. Carbohydrates and protein each supply about 4 calories per gram, while fat supplies about 9.
Macronutrients are distinguished from micronutrients — vitamins and minerals — by quantity and by function. The body requires macronutrients in gram quantities every day, and each one both provides energy and serves structural or regulatory roles. Carbohydrates are the primary fuel for high-intensity work, stored as glycogen in muscle and liver. Protein supplies amino acids for building and repairing tissue, including muscle. Fat is the densest energy source, forms cell membranes, and carries the fat-soluble vitamins A, D, E, and K.
Energy density differs across the three. Carbohydrate and protein each yield roughly 4 kilocalories per gram; fat yields about 9. That difference explains why a small change in dietary fat has an outsized effect on total calorie intake. Alcohol supplies about 7 kilocalories per gram but is not classified as a macronutrient because it serves no structural or regulatory function.
Which macronutrient dominates as fuel depends on exercise intensity and duration. At low intensity, fat oxidation supplies most of the energy. As intensity climbs, the body shifts progressively toward carbohydrate, because glucose can be broken down quickly through glycolysis and can be used without oxygen when demand outstrips supply. Protein contributes only a small share of energy during exercise under normal conditions; its main training role is supporting the muscle protein synthesis that drives adaptation. Practical intake targets are usually expressed relative to body weight and adjusted for the athlete's sport and training phase.
Sports nutrition is a tested domain on the NSCA Certified Strength and Conditioning Specialist (CSCS) exam, which covers macronutrient roles, energy yields, and intake recommendations for athletes alongside vitamins and minerals. The MBLEx also touches nutrition and physiology fundamentals in the context of body systems and the effects of soft tissue work.
Key takeaways
- The three macronutrients are carbohydrates, protein, and fat.
- Carbohydrate and protein each supply about 4 kcal per gram; fat supplies about 9 kcal per gram.
- Carbohydrate is the dominant fuel at high exercise intensities; fat contributes most at low intensities.
- Protein's primary training role is tissue repair and muscle protein synthesis, not energy supply.
- Vitamins and minerals are micronutrients — needed in far smaller amounts and supplying no energy.