A bit of history; The Fanny Farmer Cookbook (1896) introduced macronutrients as we know them today. It classified food as being composed by the following as either "Proetid (nitrogenous or albuminous), a Fat or Oil, or a Carbohydrate (sugar or starch). This new, simplified breakdown of food immediately began influencing our approach to food and diet. What was once understood holistically — meat, hand-pressed oil of known origin, and potatoes — would now be seen as the macronutrients of proteins, fats, and carbohydrates.

Macronutrients are considered chemical substances that humans consume in large quantities to obtain energy. Compared to vitamins and minerals, macros have calories, and thus, they are important for survival even in the short-term. An exception to this rule is carbohydrates, which technically are not essential because the liver can make glucose from fats and proteins in a process called gluconeogenesis. Thus, exogenous carbohydrates are not technically necessary for survival, but they are very important for optimal performance and recovery. Fats have 9 calories per gram and proteins and carbohydrates have 4 calories per gram. The vast majority of foods have a certain amount of all three of these macros. However, most foods are typically either high in proteins, fats, or carbohydrates. The macronutrient ratios in the diet are going to have a profound impact on body composition, appetite, hormone levels, and certainly athletic performance.