Macronutrients: Carbohydrates, Proteins, and Fats

The three macronutrients—carbohydrates, proteins, and fats—supply the body with both energy and the structural materials needed for growth, repair, and metabolic function. Carbohydrates and proteins each yield approximately 4 kilocalories per gram when oxidized, while fats are more energy-dense, providing about 9 kilocalories per gram; alcohol, though not a nutrient required for health, contributes roughly 7 kilocalories per gram when consumed. Unlike micronutrients, which are needed in milligram or microgram quantities, macronutrients are required in gram quantities daily, often tens to hundreds of grams, because they form the bulk of both dietary intake and body mass. Beyond their caloric role, each macronutrient class performs functions no other class can fully replace: carbohydrates fuel the central nervous system and support high-intensity exercise, proteins supply amino acids for enzymes, hormones, and tissue repair, and fats provide essential fatty acids, carry fat-soluble vitamins, and form the structural basis of cell membranes. The relative proportions of these three macronutrients in a diet, often expressed as a percentage of total energy intake, vary widely across cultures and individual health goals, yet all three remain indispensable in some minimum amount for normal physiological function.