Answer
The main food sources of calories are carbohydrates(CHO), proteins and fats. However, these nutrients are not equal in their potential for supplying energy.
Proteins and carbohydrates supply about 4 kilocalories per gram (4 kcal/gm) when they are completely oxidized. Fat is a superior energy source because oxidation of fats yields about 9 kcal/gm-- more than twice the yield of CHO and proteins.
Work Step by Step
Some foods like alcohol (7.1 kcal/gm), and some sugary foods are said to supply "empty calories." What this means is that these foods yield calories capable of suppressing appetite and supplying energy, but they are devoid of other nutrients that are essential for complete nutrition and good health. In the case of alcohol. this substance has several toxic effects on the liver and other organs; therefore, it should be regarded not simply as a source of empty calories, but as a potential mild metabolic toxin that should be consumed with care.
Beneficial and healthful food substances at once supply the body's requirements for proteins, carbohydrates, lipid, and micronutrients.
