The energy of nutrients
Cells obtain energy from the oxidation of nutrients (provided by the digestive system), which combine with oxygen from the air we breathe in (respiratory system), which reach the cells through the circulatory system, and whose remains from this oxidation are eliminated by the excretory system.
All nutrients do not provide the same amount of energy:
- One gram of lipids gives us 9 Kcal (38 Kj).
- One gram of carbohydrates gives us 4 Kcal (17 Kj).
- One gram of protein gives us 4 Kcal (17 Kj).
Cells obtain energy from carbohydrates, but when they need it, they turn to the reserve we have in the form of lipids. The proteins are used as a source of energy only exceptionally, when the body is in a state of malnutrition.
How much energy do we need?
The energy that a person needs each day depends on several factors such as sex, age, weight, and above all, on physical activity.
- The energy used to perform basic functions such as breathing, the movements of the heart or maintain constant body temperature.
- The energy used to perform physical activity, such as walking, or playing sports.
The BMR is the minimum amount of energy that a person needs to survive. It is calculated after having been completely resting in a place with a comfortable temperature (20 ° C) and having fasted 12 or more hours.
The basal metabolism is calculated in kilocalories / day and depends on gender, height and weight, among other factors, such as body mass.