What is the primary source of energy for humans?

There are 3 different sources of energy (known as macronutrients) which are carbohydrates, protein, and fat. Out of these three, carbohydrates are the main source of energy (or the preferred one). Carbohydrates ae what breaks down into glucose and is a fast source of energy especially for the brain and other muscles.

There are 3 sources of calories (or energy), which are also known as macronutrients: carbohydrates, protein, and fat. Of these three, carbohydrates are the body's preferred source of energy. Carbohydrates break down into glucose, which is an immediate source of energy especially for the brain and muscles.