Net energy is the energy content of foods that covers the energy used by the individual (maintenance, labor, lactation, ...) and allows savings of body reserves. It corresponds to the metabolizable energy (ie digested in the small or large intestine; the remainder is eliminated in the stool, 1/3 for hemicelluloses and 3/4 for fruit and vegetable fibres) less heat generation associated with the metabolism of nutrients for the supply of free energy to the cells, or lipogenesis, ... These heat losses depend on the nature of the nutrients (glucose, acetate, amino acids, fatty acids) and how they are metabolized. It corresponds to the real energy value of foods, as indicated in the CIQUAL table. Their transformation into kilocalories (the unit we use) or kilojoules (1 kcal = 4.185 kJ) requires foods to be tested in a calorimeter (combustion of the food to measure the amount of heat produced).

The energy value of the food in the database is defined by burning these food in a laboratory and collecting the amount of energy emitted. But in the body, the use of this energy is not the same for each type of nutrient, particularly for carbohydrates (based on the glycemic index) and lipids (depending on the type of fats, saturated and unsaturated).

What counts more, is the energy balance that is the difference between intake and consumption

Energy consumption are of several types:

  • Basal metabolism. This is the amount of energy necessary for the vital functions of the human body
  • Food Thermogenesis . Food intake increases energy expenditure of an individual at rest, and in proportion to the quantity of energy intake.
  • Thermoregulation. Energy is consumed to maintain body temperature at 37 to 37.5 ° C, when exposed to low outside temperatures.
  • Physical activity. It is the second variable in enegy consumption, based on weight and body composition.

The causes of energy imbalance , may be :

  • Food
    • fat consumption is a major contributor to increased caloric intake because of the density of high fat content foods high compared to other macronutrients.
    • the disruption of eating habits (no breakfast or lunch, snacking, especially watching TV), and eating between meals (including impulsive eating) contribute greatly to the increase in calories.
    • Alcohol seems, in some individuals, to favour weight gain due to calorie intake, its effects on fat oxidation and its effects on impulsivity, especially food
  • physical activity : physical inactivity promotes weight gain and obesity
  • genetic factors
  • Societal factors. Lifestyles influence eating habits and exercise :
    • industrialization and urbanization have reduced energy expenditure. Phyiscal activity is limited to leisure time and is volontry
    • organization of school time leaves limited time for physical activity and education. Physical exercise for children, has beneficial effects on corpulence and eating behavior
    • changing eating habits is characterized by a decrease in the consumption of complex carbohydrates, fruits and vegetables and an increase in animal fat and sugary foods
    • the ambient temperature of housing has increased
    • many widely available and currently consumed foods have a high caloric density (eg pastries, crisps, sweets and sugary drinks as compared to water ...)

Energy sources

See the list of foods that provide the most energy


Scientists separate the calculation of energy requirements into two parts :

  • that linked to basal metabolism. Depending on gender, weight, height and age, a formula (Black et al equation) to determine the amount of energy needed to maintain basal metabolism
  • that related to the activity. An activity coefficiant (generally between 1.2 and 2) used by multiplying the basal metabolic rate so as to determine the daily energy requirement. To facilitate this assessment, The Nutriomètre ® proposes five generally used levels of activity, from which you should choose to calculate your energy needs and thus balance your energy intake.

Source: "Recommended dietary allowances for the French population," CNERNA-CNRS. Edition coordinated by Ambroise Martin.)