Energy needs

Our organism needs a continuous supply of energy to enable it to breathe, grow, maintain temperature, repair tissues, among many other functions. We obtain this energy mainly from carbohydrates, lipids and proteins, which are the basic nutrients contained in food.

The caloric value of foods varies according to their macronutrient content, for example, the most caloric are fats, followed by proteins and carbohydrates and finally dietary fiber.

The energy or caloric value of food

It is the amount of energy produced when a food is totally metabolized, to produce carbon dioxide and water (and also urea in the case of proteins). The unit of measurement in which it is normally expressed is kilocalories (kcal).

The approximate amount of energy provided by each of the nutrients per gram metabolized is as follows:

• Fats contribute 9 kilocalories per gram.

• Carbohydrates contribute 4 kilocalories per gram.

• Proteins contribute 4 kilocalories per gram.

• Dietary fiber contributes approximately 2 kilocalories per gram.

• Water, vitamins and minerals do not supply energy to the body.

Alcohol, although not a nutrient, contributes 7 kilocalories per gram metabolized.

To ingest a certain level of calories, we must consume more or less quantity of food depending on the type of these. For example: a spoonful of oil contributes 100 kilocalories, nevertheless if we wanted to obtain 100 kilocalories consuming oranges we would have to ingest two medium oranges.

Other examples:

• 1 cafeteria packet of butter of 13 grams = 100 kilocalories.

• 1 large glass of juice of 250 milliliters = 100 kilocalories.

Caloric profile

The caloric profile is defined as the amount of energy contributed by each of the macronutrients (carbohydrates, fats and proteins) to the diet.

Recommended caloric profile: a balanced, prudent and healthy diet should provide the required energy distributed among the different macronutrients as follows:

• More than 50% of the required calories should be provided by complex carbohydrates, such as vegetables, whole grains, whole wheat bread and pasta.

• Between 30 and 35% should be provided by fats.

• Between 10 and 15% should be provided by proteins.

If there is any moderate alcohol consumption, its caloric contribution should never exceed 10% of the total calories.

In general, diets at present do not meet the requirements of the calorie profile recommended by specialists. In poor countries, most of the population obtains up to 80% of its energy from carbohydrates, provided mainly by cereals, while in more developed societies, diets are dominated by foods of animal origin, rich in proteins and fats, with low carbohydrate content.

Energy expenditure

The daily energy expenditure of the organism is produced by the demand of three important components, these are:

• Basal metabolism (mb).

• Thermogenic effect of dietary food (etd).

• Physical activity (af).

Basal metabolic expenditure: includes the energy required to maintain the vital functions of the organism under resting conditions, such as blood circulation, respiration, tissue growth in children, etc. Unless physical activity is very high, this is the largest component of energy expenditure, and in sedentary people it can represent 70% of their total energy needs. Basal energy expenditure depends on body composition, being higher in people with greater muscle mass and less fat.

The thermogenic effect of dietary food (TDE): this is the energy required to carry out the processes of digestion, absorption and metabolism of the components of the diet, after the consumption of food in a meal. It includes the secretion of digestive enzymes, the transport of nutrients, and the formation of body tissue reserves. It can account for 10-15% of an individual's total energy needs, depending on the characteristics of the diet.

Physical activity (PA): is the energy expended throughout the day to perform work and physical activity. It is the most important factor because it is modifiable and depends on the type, duration and intensity of the physical activity performed. The following examples show the approximate energy demands of some activities:

• One hour sleeping: 75 kilocalories.
• One hour sitting talking or watching TV: 120 kilocalories.
• An hour driving a car: 180 kilocalories.
• One hour playing tennis: 460 kilocalories.
• One hour riding a bicycle: 500 kilocalories.
• One hour swimming: 730 kilocalories.
• One hour climbing stairs: 1000 kilocalories.

Calculation of daily energy needs

Daily energy needs: the energy we need to obtain through food to carry out all our daily activities, maintaining a balance between intake and expenditure, which allows us to maintain an adequate and constant body weight.

Calculation of daily energy needs: there are several methods for estimating energy needs based on basal or resting metabolic rate (BMR) and parameters related to physical activity. When greater precision is required, tables are used that show the energy expenditure per physical activity, expressed in kilocalories per kilogram of weight, and the time taken to perform the activity.

Calculation of daily energy requirements based on the resting metabolic rate (RMR) and average physical activity factors: this is obtained by multiplying the basal metabolic rate (RMR) by the physical activity coefficient (fa):

• Daily energy requirements = RMR x fa

Procedure for calculating daily energy requirements:

• We first calculate the resting metabolic expenditure (TMR), for this we will use the harris-benedict formulae (table n° 1), starting from the weight (p), the height (t) and the sex of the individual.

• Finally, we multiply the value of the (TMR) obtained by the appropriate (fa) and we obtain the value of the daily energy needs expressed in kcal/day.

Elements for classifying physical activities as light, moderate and high

Light: light physical activities are performed by people who do not practice sports regularly and spend several hours of the day in sedentary activities, in front of the computer, watching TV, conversing, performing light household activities, driving, working in an office, and who perhaps once or twice a week perform some moderate physical task.

Moderate: moderate physical activities are performed by people who walk frequently, do heavy household chores, perform their work in constant movement without doing too heavy tasks, such as carpenters, electricians, plumbers, some builders, domestic workers, etc.

High: jobs or sports that require great physical effort for several hours are considered to be high physical activities. Examples: people who commute daily by bicycle or walk long distances, practice sports daily for several hours, agricultural workers who perform non-mechanized tasks, miners, firewood cutters, active soldiers, dancers, among others.

Balance between energy needs and intake

The balance between energy needs and the amount of food we consume is the main factor in maintaining a stable body weight. If the daily diet provides more energy than the body needs to perform all its tasks, the excess is stored as fat, leading to overweight and obesity.

If, on the other hand, the intake does not provide enough energy to support the expenditure, the body takes the necessary energy from the body's fat and protein reserves, causing weight reduction and malnutrition.

Imbalances in the energy balance always represent health risks; energy deficits and excesses in the organism favor the appearance of numerous ailments, which drastically reduce the quality of life and life expectancy.

Adequate weight is achieved with a healthy diet and regular physical activity.