We all need energy to function and we get this energy from the foods we eat. The most efficient way for cells to harvest energy stored in food is through cellular respiration, a catabolic pathway for the production of adenosine triphosphate (ATP). ATP, a high energy molecule, is expended by working cells.
An Apple a Day. The calories in a McIntosh apple depend on its size. According to the U.S. Department of Agriculture, a medium-sized apple with its skin has about 95 calories. Eating an unpeeled apple is moderately higher in calories than a peeled apple, but don't rush to peel your apple.
Fresh, dried, or as apple juice or cider are all ways to enjoy apples. A medium sized (180g) raw eating apple, including the skin, provides around 85 calories. Around 85% of an apple is water, approximately 14% is carbohydrates - mainly as the sugar fructose - and the remaining 1% by weight is protein and fat.