You are probably aware that we continually need energy . Our favorite energy source ? The nutrients concentrated in our food . But how can we, with intermittent food intake (morning, noon, evening), cover continuous energy needs ? This exceptional machine that is our body has developed an extraordinary storage system for energy substrates . We therefore store part of the energy we consume and spend the rest. The challenge ? Consume and store as much as you spend to maintain a healthy weight . Every day is a real balancing act to stabilize the energy intake/expenditure balance. We invite you to better understand your body so that you are no longer afraid of stepping on the scale ! Because did you know that calories are in fact a concentrate of energy and are not intended to make you gain weight ? It's all a question of balance !
I. Energy balance.
The energy balance contrasts energy intake (food intake of nutrients: lipids, proteins, carbohydrates) and energy expenditure . For good health , neither should take precedence over the other: this is the principle of conservation of energy : the energy supplied must be equal to the energy spent . For this, it is neither created nor destroyed but only converted into another form. Thus, the so-called “ chemical ” energy provided by the nutritional substances will be used by the body in this same form, for lactation for example. Or the body will expend it in the form of caloric energy , inherent to life. But it can still transform it into mechanical energy , for physical activity. Finally, it is even able to transform it into electrical energy , even if this is negligible!
To balance this energy balance , scientists have developed experimental methods to measure the average expenditure of individuals, according to their age , weight and sex and thus define the energy needs that their food ration must cover.
II. Energy expenditure: where does the energy go?
When we think of energy expenditure , we necessarily associate it with sport : if we do not practice physical activity , we do not eliminate it: This is FALSE! There are 4 areas of energy expenditure , including sports exercise .
1) Basic metabolism
Basic metabolism corresponds to the implementation of all our vital functions (cerebral, metabolic, etc.). It is measured when the body is at complete rest, lying down, fasting for 12 hours and at the temperature of thermal neutrality in order to exclude the involvement of any other item of expenditure ( physical activity, digestion , thermoregulation ).
Its contribution to energy expenditure amounts to 45-70% , or 1500kcal eliminated in 24 hours in young adults and 5% less when the subject is asleep. Of course, these numbers are inherently dependent on the individual. Certain factors vary the energy expended via the basal metabolism . Thus, a man will expend more energy than a woman , just like a teenager compared to an older person. Depending on the size and activity of each person's organs, differences will be notable. Indeed, the heart (continuous and automatic functioning), the kidneys and the brain use a lot of energy . Conversely, adipose tissue (fat) does not cause any expenditure, whatever its volume or mass. A person's body fat therefore has no influence on their resting metabolism . On the other hand, muscle mass is important because the larger the muscle , the more energy it expends at rest and the more the basic metabolism increases. This explains why, as we age , our basic metabolism decreases: we lose muscle !
Doing bodybuilding, for example, therefore proves to be an excellent way to increase your basic metabolism and more effectively counterbalance food consumption .
2) The specific dynamic action of foods or food thermogenesis
It may be counterintuitive, but food contributes to energy expenditure . Indeed, when they are assimilated in the liver , exothermic biochemical reactions occur, that is to say which release heat . This heat actually corresponds to the energy spent. This is why when we eat, we are overcome by a warming sensation, especially when ingesting a meal rich in protein . In fact, proteins , which are a succession of smaller molecules called amino acids, will undergo a particular metabolization called deamination. This separation of different amino acids consumes twice as much energy as lipids or carbohydrates .
This is why high-protein diets can be interesting as part of a weight loss program, especially since these nutrients , unlike lipids and carbohydrates , are not stored.
You all know, our body temperature is 37°C . It should not vary from this set point and if this is the case, the body does everything possible to restore it. At an outside temperature of 25°C , thermal neutrality is considered to be achieved. If it ever cools , the body will use a large amount of energy to return to 37°C . The cold will also cause involuntary contraction of the skin muscles (shivering) which will result in significant energy expenditure . Unfortunately in cases of obesity , body temperature can vary and energy expenditure can vary because fat acts as an insulator .
When temperatures increase, the body will use energy to cool itself, but much less than when it heats up . It will also stimulate perspiration to cover the skin with water and give the sensation of cooling during movement .
4) Muscular work
This item of expenditure plays a vital role in the energy balance . It does not necessarily involve practicing a sport but only the act of moving . This movement will accelerate the heartbeat , put the blood vessels under tension and condition the vascular state. It will modify the metabolism in depth. The expenditure will be strongly linked to the intensity and duration of the exercise.
III. Energy needs and their coverage
1) Quantification of energy needs
Based on the in-depth assessment of energy expenditure and the factors influencing them, scientists have defined energy needs . They actually quantified the energy needed to provide the body in calories (kcal) according to age , weight , sex and physical activity . These quantifications are average estimates that differ greatly from one individual to another. You will find an overview in the table below:
In case of special life situation, the needs also differ:
- Pregnant women :
- 1st trimester: +15 kcal/day
- 2nd trimester: +120 kcal/day
- 3rd trimester: +310 kcal/day
- Breastfeeding women: +500 kcal/day
- Infants - Children:
- Birth to 3 months: 100 kcal/kg/day
- Average 1st year: 92 kcal/kg/day
- 1 to 9 years: 75 kcal/kg/day.
- Adolescents: 50 kcal/kg/day
2) Energy intake through food intake
Food helps meet energy needs thanks to its supply of nutrients : proteins , carbohydrates and lipids . Each provides a quantity of energy that can be metabolized by the body:
- Protein: 4 kcal
- Carbohydrates: 4 kcal
- Lipids: 9 kcal
It should also be noted that quality is important: not all calories are nutritionally equal: there are calories with high nutritional values and empty calories.
For example, plant proteins are not as good quality as animal proteins . However, animal proteins provide a lot of fat and therefore a balanced mixture of the two types ensures a supply of quality proteins without excess lipids .
There are also different qualities of lipids (saturated, polyunsaturated and monounsaturated) and carbohydrates (simple and complex).
The perfect food ration is balanced :
- 50-55% of energy provided in the form of carbohydrates .
- 30-35% of energy provided in the form of lipids .
- 10-15% of energy provided in the form of protein
To meet an energy requirement of 2000 kcal, you therefore need 250 g of carbohydrates, 88g of lipids and 50g of proteins.
You now know how you spend your energy, what your energy needs are and the quantities of nutrients you need to consume to achieve the dream goal of energy and weight balance!