For those wanting to nerd out.
The macronutrients, or macros if you want to sound cooler, are dietary compounds that we consume in relatively larger quantities, and include carbohydrates, protein and fat. These 3 are our major source of fuel (calories), but also play many other unique and important roles in our bodies.
Most foods contain all 3 macros, and once ingested, they make their way through our digestive system, where they're broken down into smaller components. Once in the small intestine, these micro-particles are absorbed in our bloodstream where they play unique roles in our target organs.
Through a process called cellular respiration, all three macros can be used to form ATP (adenosine triphosphate), the main source of cellular energy.
The recommended daily ratios of macros for optimal health are 45-65% of calories coming from carbohydrates, 20-35% coming from fat and 10-35% coming from protein. Obviously, manipulating and fine-tuning these ratios is what will help athletes achieve peak performance, and the macro split of a long-distance runner will be much different than that of a bodybuilder. It's also important to keep in mind that for certain specific conditions, including medical reasons, the recommended macronutrient split may be modified by your healthcare provider.
Carbohydrates are the body's main fuel and preferred energy source. Most calories should come from carbohydrates. They provide 4 calories per gram. For more on carbs, including the difference between good carbs and bad carbs, as well as the difference between complex and refined carbs, go check out the For Nerds section on Carbs.
Protein are the building blocks of the body and aid in tissue growth and repair. Like carbs, they provide 4 calories per gram and can be used as fuel when carbs are not available. Other than serving as an alternate source of fuel, protein serves other major roles in the human body, including immune function, hormone production and enzyme synthesis. For more on protein, please see the For Nerds section on Protein.
Fat also provides fuel for the body when needed and provides 9 calories per gram, more than double that of carbs and protein. They're absolutely necessary for proper absorption of fat-soluble vitamins A,D,E,K, and serve many other important roles in the body. They are the main component of the cellular wall and the most energy dense of all 3 macros. For more on fat, including the differences between good and bad fats, saturated and unsaturated, as well as trans-fats, please visit the For Nerds section on Fats.
To learn specifically about macronutrient splits for athletes, click to jump to the For Athletes page.