Why Fats have highest heat energy density?

Fats have highest heat energy density of 9 Kcal/g. It is the major storage form of energy in body requiring least space and minimum water of hydration as compared to protein in muscle or glycogen. Adipose cells are 80% lipid and only 20% water and protein. In children's diet, cereals and pulses make their diet bulky. Fats are concentrated sources of energy. In adult's diet, use of visible fats should be minimum. Excessive fat intake is not recommended in any age, including children.