The short answer is the food you eat. However, that's a little too bland. The foods we consume contain lipids (fats and oils), proteins (amino acids), carbohydrates (sugars and starches), and other chemical compounds that keep energy stored in their chemical bonds (alcohols, nucleic acids, etc.). When you eat, your body digests the foods and extracts the compounds through the intestines. The circulatory system picks up the nutrients and circulates them through your body to your cells. To some degree, all cells store some energy. In the case of neurons, little energy is stored, whereas adipose (fat) tissue stores a great deal of lipids. During physical activity, the cells consume available stores of energetic compounds (carbohydrates, proteins, and lipids) in order to keep working. After prolonged activity, the stored energy is depleted and the cells begin to take up carbohydrates from the blood. Once these supplies are depleted, the body goes through a complex process of converting stored energy from fat into usable energy. As a result, it usually takes a great deal of exercise to "burn off" fat.
ATP - Adenosine Tri-Phosphate.
the uses of energy is to do work or to work the transport such as:train,planes,cars,e.t.c.......
it converts carbohydrates into energy and uses them when you do physical activities
The brain is the organ in the human body that uses the most energy.
The body first uses carbohydrates for energy, then it uses fats, and finally it uses proteins as a source of energy. Proteins are typically used as an energy source only when carbohydrates and fats are unavailable.
Energy
A calorie is a unit of heat used to measure the energy your body uses and the energy it receives from food. It represents the amount of energy required to raise the temperature of one gram of water by one degree Celsius.
Glucose
The brain uses the most energy in the body, accounting for about 20% of the body's total energy consumption. Other organs, like the heart, liver, and kidneys, also require substantial amounts of energy to function properly. Muscles can also consume a significant amount of energy during physical activity.
Fat is stored energy. When the body needs extra energy - it uses up body fat.
The five main uses of energy in the human body are for metabolism, physical activity, maintaining body temperature, growth and development, and cellular processes.
every thing