Food is a fuel for our body. The energy that we get from food is chemical energy. Our body can convet this chemical energy into mechanical power or heat. Nutrients that release energy are carbohydrates, fats and proteins. Other classes of nutrients, such as vitamins, minerals and water do not produce any energy.
Let us remind that a calorie is a very small unit. It is so small that when we eat one apple we get ten of thousands of calories. In order to simplify the calculation, energy is measured in 1000 calorie unit which is called kilocalorie (kcal). So when we read somewhere that an apple contains 60 calories, it is meant to say that it contains 60 kilocalories.
How much energy we get from certain food depends on how much carbohydrates, fats and proteins it has. One gram of fully split carbohydrates release about four kilocalories of energy, one gram of protein – also four kilocalories and one gram of fat – nine kilocalories of energy. Most of the foods contain all three components that release energy and also water, vitamins, minerals and other substances.
How many calories we need depends on several things: weight, age, sex, the nature of work and rest. Women need at least 1200 kilocalories and men at least 1500 kilocalories. However, athletes may take up to 5000 kilocalories per day as they work out a lot and burn a big part of consumed calories.
An average person should get 55-65 per cent of calories from carbohydrates, 20-25 per cent from proteins and only 10-25 percent from fat. In order to maintain ideal body weight, we should calculate not only how many calories we get but also how many calories we burn.