Fats, carbohydrate and sugars are sources of energy.
If you are looking for long release energy eat carbohydrates like: Pasta, rice and bread.
If you are looking for quick release energy eat sugars: fruit or chocolate.
In most food webs the Sun is the ultimate source of energy. Some food webs start with chemotrophs and in those cases the source of the energy are chemicals often from underwater volcanoes.
from food
Yes fats are the most calorific energy source.
the source for all enery is sunlight
No Food under normal circumstances is a renewable source of energy. Food is the result of plants getting energy from the sun and converting this energy into storage. the plants can the be eaten and the energy used. The plant however puts out seed and grows again renewing itself as a source of energy.
plants
Food stores fat. Fat is an energy source of the body.
carbohydrates
food
the sun
Nutrients and energy.
The food it eats.