Diet and nutritional needs of the adult.

Adulthood begins when the individual has reached a complete degree of growth and development, including the capacity to reproduce. At this stage, the phases of rapid growth and modification of body composition have been overcome, so there are no longer the high energy and nutritional demands of the previous stage.

In adults, an adequate diet is necessary to achieve an optimal nutritional state, essential to maintain good health, delay or reduce deterioration over the years and prevent the occurrence of chronic diseases with a nutritional basis.

Energy needs

The energy needs of adult individuals are determined by basal metabolism, food-induced thermogenesis and physical activity. These components are affected by variable factors such as the following:

• Age.

• Body size.

• Body composition.

• Sex.

• Level of physical activity.

Age: between 16 and 39 years old, the recommended energy intakes for moderate physical activity are 2300 and 3000 kilocalories, for women and men respectively. From the age of 40 onwards, energy consumption should be moderated to avoid overweight and obesity and, consequently, the appearance of chronic diseases such as hypertension and diabetes, among others.

Size: although people are of the same age and sex and have a similar level of physical activity, they need to receive different amounts of energy depending on their size; taller people need higher levels of energy from their diet.

Body composition: energy requirements are also greater when the lean tissue or fat-free mass (FFM) of the organism is greater, so that individuals with greater muscle mass (the most important component of the FFM) demand higher levels of energy.

Sex: the GLM is greater in the male sex, so they demand more energy than the female sex.

Level of physical activity: people who perform moderate or intense physical activities need more energy than those who lead a sedentary life. For example, a person who spends one hour sleeping should expend about 80 kilocalories, watching television or chatting about 120 kilocalories, walking 160 kilocalories and climbing stairs about 1000 kilocalories.

Assessment of the energy levels provided by the diet: To evaluate in a simple way if the energy levels provided by the diet are in correspondence with the energy needs of the individual, the body mass index (BMI) of the individual can be found; if the value of this parameter is within the appropriate range, the amounts of energy ingested are in correspondence with the demands; if the index is lower, the diet is deficient, and if on the contrary it is higher, the calories provided by the diet exceed the allowed limits.

The BMI is calculated by multiplying the weight of the individual, expressed in kilograms, by the square of the height, expressed in meters. For example: to calculate the body mass index of a man weighing 70 kilograms, who is 1.80 meters tall, proceed as follows:

• BMI = body weight in kilograms / (height in meters)².

• BMI = 70 kg / 1.80 m x 1.80 m

• BMI = 70 kg / 3.24 m² (3.24 sqm)

• BMI = 21.6 kg/m²

As the result is between 18.5 and 24.9 kg/m², we can affirm that the body mass index is adequate, therefore the energy levels provided by the diet are correct.

Carbohydrate requirements

Carbohydrates, in addition to their energetic role, are fundamental in the metabolism of the nervous centers, since glucose provides almost all the energy used by the brain on a daily basis. They also confer flavor and texture to food and thus contribute to the pleasure of eating.

It is recommended that a balanced diet should include more than 55% of the total energy consumed in the form of carbohydrates, mainly complex carbohydrates (bread, pasta, potatoes and legumes) as they contribute to the control of body weight and in the prevention of cardiovascular diseases, diabetes, some types of cancer and some gastrointestinal disorders.

It is recommended that the caloric intake of simple carbohydrates (table sugar, sweets, pastries, pastries, chocolates and soft drinks) should be less than 10% of the total energy consumed. These foods, eaten in excess, can contribute to reducing the nutrient concentration of the diet, as they are a source of empty calories.

Lipid requirements

Fats in the diet contribute to the digestibility and palatability of foods; their main function is energy supply. In addition, they play structural roles in the formation of membranes and participate in the synthesis of neurotransmitters.

Fat consumption should not exceed 30% of the total calories in the diet; however, in Spain, up to 35% is allowed, given the habitual consumption of olive oil as a culinary fat. It is recommended that the total lipid intake be obtained from the different types of fats, in the following proportions:

• 15 to 20% monounsaturated fatty acids, which come mostly from olive oil.

• Between 7% and 8% of saturated fatty acids, which are found in foods such as whole milk, butter and fatty meats.

• Between 7% and 8% polyunsaturated fatty acids, found mainly in oily fish, nuts and seed oils such as sunflower, corn and soybean oils.

When lipid intakes fail to provide more than 30% of the total energy needed by the body, deficiencies of fat-soluble vitamins (a, d, e, k) and minerals such as calcium, iron and zinc may occur.

Protein needs

Proteins are the main constituent of cells, necessary for the growth, repair and renewal of body tissues subjected to continuous wear and tear. They also provide raw materials for the formation of digestive juices, hormones, plasma proteins, hemoglobin, vitamins and enzymes. They can be used to supply energy when carbohydrates and fats do not provide the necessary energy and also function as buffers, thus helping to maintain the reaction of various media, such as plasma, cerebrospinal fluid and intestinal secretions.

In the adult stage, the individual needs proteins for conservation purposes. Thus, they are constantly decomposed and replenished in the tissues, following different cycles in the different organs, with some structures being renewed every three or four days, such as the epithelial layer of the intestinal tract, while others, such as collagen, a protein present in tendons, bones and connective tissues, are renewed slowly.

That is why the recommended intakes for this stage are estimated at 41 and 54 grams per day, for women and men respectively, figures lower than those recommended for adolescence. It should be taken into account that people who make a great physical effort during work or sports practice also increase their muscle mass and therefore need supplementary proteins, although the amount needed is probably not very considerable. How to select proteins for the diet?

Not all proteins contain all the essential amino acids in sufficient quantities to satisfy human needs. A biologically incomplete protein lacks one or more essential amino acids. Proteins of animal origin contain more essential amino acids than those of vegetable origin and in general have a higher nutritional value.

Most plant foods lack one or more essential amino acids. In order to obtain all the essential amino acids by consuming only vegetable proteins, we must ingest in the same meal, two products of vegetable origin, which complement each other. For example:

• Cereals have low contents of one or several essential amino acids, rice is poor in lysine and threonine, wheat in lysine; while legumes contain up to 25% of proteins rich in lysine, thus complementing the proteins of cereals that are poor in lysine. Diets based on a mixture of cereals and legumes have a higher nutritional value than those based on cereals or legumes alone.

• Animal proteins, in addition to being more complete and nutritious, can be used to effectively supplement poor diets of vegetable origin. It has been shown that whole milk proteins can complement those provided by bread or potatoes. The protein needs of adults can be effectively met with mixtures of vegetable and animal proteins.

Vitamin requirements

Although the daily needs of vitamins consist of doses of only a few milligrams, their role in the health is not limited to avoid the diseases that their deficiencies provoke, since they are essential elements for the maintenance of the functions of the organs and tissues that integrate the organism. In addition, they also have a protective role, preventing the onset of certain degenerative diseases such as cancer, cataracts and cardiovascular diseases.

In general, the consumption of a varied and sufficient diet guarantees the necessary intakes of vitamins in adults; however, there are population groups at risk due to different circumstances, such as weight loss regimes not planned by health personnel, alcoholism, smoking and chronic diseases.

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