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At its origins, the calorie is a unit of measurement in physics, defined as the amount of heat required to raise the temperature of one milliliter of water by 1 ° C.

From a dietary point of view, the energy value of a food corresponds to the amount of heat released by its burning. The kilocalorie (kcal) is equivalent to 1000 calories and the international unit is the kilojoule (Kjoul), 1 kcal = 4.18 kjouls.

We can equate the word calorie with kilocalorie. We can do the same equivalence in terms of calories that our body consumes! To get an accurate idea, we must know that:

  • 1 gram of carbohydrates equals 4 kilocalories;
  • 1 gram of proteins equals 4 kilocalories;
  • 1 gram of lipids equals 9 kilocalories;

In order to function, our body needs calories. Here are some common activities that require burning calories:

  • within an hour of sleep or rest, the body burns 60 calories;
  • within an hour of activity in sitting position (TV, computer, reading, transport …): 90 calories;
  • within an hour of activity in the standing position (washing, dressing, household chores …) 120 kcal are consumed;
  • within an hour of gymnastics, gardening, walking 170 kcal;
  • 1 hour of sports (skiing, tennis, cycling …) or intense professional activities 300 kcal are consumed.

The energy intake of an individual is “the amount of energy required to compensate the consumption and to ensure a body weight and a consistent body composition compatible with long-term maintenance of a good health and physical activity adapted to the economic and social context” (OMS, 1996).

To calculate the recommended energy intakes, we must consider both the basic energy consumptions, as well as the energy consumptions induced by particular physiological situations: growth (proteins and lipids storage), pregnancy (fetal and placental growth), and nursing (milk production)…

In addition, to assess the energy needs the weight must be taken into account, as well as the height and the physical activity of each individual.

  • Men between 20 and 40 years old (70 kg) need 2700 kcal;
  • Women between 20 and 40 years old (60 kg) need 2200 kcal;
  • Men between 41 and 60 years old (70 kg) need 2500 kcal;
  • Women between 41 and 60 years old (60 kg) need 2000 kcal.

Ideally, the energy intake must be distributed in a balanced manner throughout the day: between 20 and 25% at breakfast, between 25 and 30% at lunch, between 15 and 20% for snacks and between 25 and 30% for dinner.


The dietary balance is at least as important as the number of consumed calories. For example, a person who consumes 1500 kcal, but does not have a balanced diet can gain weight while a person consuming 2000 kcal can successfully maintain weight.

Why do we gain weight?

Because we provide the body with more calories than it needs daily (this depends also on the metabolism, as it, for some people, works better, meaning that it can also burn the excess we give it and thus the weight gain phenomenon no longer appears).

How can we avoid gaining weight?

If we stay within the limits set by the calories, for each category (according to age, sex, type of activity, etc.) we will not gain weight.

How can we lose weight?

Simple. By reducing the number of calories set for the category we fit in and by exercise (when you give fewer calories to the body but without starving yourself – because thus, the reverse effect can occur and you gain weight – those are consumed by it. In addition, if you exercise, the body automatically starts to consume the fat deposits).

A kilo of fat equals 7000 kcal of stored energy. If you burn 7000 kcal in addition to what you consume, then you also use 1 kg of fat. By burning of 500 kcal/day in addition to what you eat, you get to lose 0.5 kg of fat per week.