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2.2.2. The energy of nutrients

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).

The vitamins, the minerals, the water  and fiber contribute nothing to the body energy but are essential for proper operation.

Cells obtain energy from carbohydrates, but when they need it, they turn to the reserve we have in the form of lipidsThe 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 expenditure is the amount of energy needed by the body to perform daily activities. It is made up of:

  • 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.

Calculation of basal metabolic rate

The following equations are used to calculate the basal metabolic rate:

Men : (10 x weight in kg) + (6.25 x height in cm) - (5 x age in years) + 5

Women : (10 x weight in kg) + (6.25 x height in cm) - (5 x age in years) - 161

You can see how it varies by changing the weight, height and age in the case of a woman :

Mass in kilos

Height in centimeters


Tasa de metabolismo basal (mujeres) = 1359 kilocalorías/día

Answer in your notebook

2.4.- How much energy do you need in a day depending on the activity you do?

This task you have to do for a week. Write down everything you eat for a week. It starts with today. Write down what you have for breakfast, lunch, lunch, snack and dinner, including approximate weight. Also if you have eaten something between meals. Later you will analyze your diet. If you prefer, you can download the template.






































































Glasses of water

Glasses of water

Glasses of water

Glasses of water

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