The most concentrated source of calories comes from

Carbohydrates.
The most concentrated source of calories comes from carbohydrates. Carbohydrates has three types: monosaccharide, disaccharide and polysaccharide. These carbohydrates are from the combined atoms of carbon that is one of the most important source of energy for an organism. In most animals, carbohydrates are modified to become glucose or blood sugar by the digestive system and delivered to many cells in the organisms’ body that is used in many cellular activity.