Energy and heat is generally obtained by burning things, or in technical term by oxidation of certain things we get heat and energy. For instance, if wood burns, then it is rapidly oxidized, the carbon and hydrogen in the word is being oxidized using the oxygen in the air while burning and this results in the generation of heat energy. Even in our body the same concept happens in a subtler way. Food energy is the amount of energy we get while our food is oxidized in our body through cellular respiration. We intake oxygen through breathing, and this oxygen is transferred to the pulmonary veins in our lungs and heart pumps that blood to all parts of the body. That oxygen is then supplied to all the cells in the body. The cells through cellular respiration takes in the oxygen and burns the food (mostly glucose). This glucose(or fat or sometime even protein while starving) will be burnt up in to carbon-di-oxide and water which is then taken back to the lungs and sent out. In the process our body generate energy (often termed as food energy). This energy is measured in calories/Kcal.
Ideal Energy Requirement for a Healthy Living
Our body and lifestyle has evolved a lot, as a result the energy required everyday for regular people keeps changing, from struggling every day for food we now live in a time where we hardly do any physical work but consume good amount of food. This is the reason for so many diseases today. People are now getting aware of the amount of calories required everyday for a healthy living. Various governments are now issuing standards for energy intake.
Food calories are often referred as kilocalories (kcal) or kilogram calories. One food calorie is equal to 4.184 kilojoules. Carbohydrates, fiber, fats, proteins, organic acids, polyols, and ethanol all release energy. However the amount of energy relased and the priority of the cells while oxidizing is different. Fat and Ethanol release the highest amount of energy, fat releases nearly 225% more energy than what Carbs releases. Complex dietary fibers are also carbohydrates, however the energy released by them are far less and the energy consumed for digesting them is higher so it is good to consume food that is rich in fiber.
Why Food Energy can be Misleading
Assume two cases one is ‘x’ amount of pure glucose having 500 kCal energy and the other is y amount of flax seeds with 500 kCal. The spike in sugar level in our body in the first case is way too high, and the second case the sugar level in the blood goes up very slowly and naturally because of very high dietary fiber level. The first case cause a lot of harm to the body and the second case results in lot of wellness to the body. So one should not be mislead by pure energy specifications alone. Instead try to consume wholesome foods with some awareness about their calories.