Energy expenditure and physical activity groups
Dietary standards are regularly revised following changes in working conditions and new scientific data. Energy requirements depend on the basal metabolic rate (BMR) and the physical activity coefficient (PAC). The entire able-bodied population is divided into groups (five for men, four for women).
- Group I (PAC 1.4): predominantly mental labor (general practitioners, educators, students).
- Group II (PAC 1.6): light physical labor (nurses, orderlies, sales clerks).
- Group III (PAC 1.9): moderate intensity labor (surgeons, drivers).
- Group IV (PAC 2.2): heavy labor (construction workers, oil industry workers).
- Group V (PAC 2.5): very heavy physical labor (miners, loaders).
Individual daily energy expenditure can be determined using precise instrumental methods (direct and indirect calorimetry) or calculation methods (multiplying BMR by PAC). In practice, the table-chronometric method is most commonly used, taking into account sex, age, body weight, profession, and time spent on various types of activity throughout the day.
Role of proteins in the diet
Proteins have no reserve stores in the body, so their deficiency quickly leads to malfunctions. They are essential for plastic, enzymatic, and transport functions. The nutritional value of dietary protein is determined by its amino acid score — a comparison with an "ideal protein" (egg and milk proteins are closest to the reference standard). Plant proteins are less digestible due to cellulose content, but thermal processing of food resolves this issue.
- Consequences of deficiency: causes developmental delays in children, decreased immunity, fatty liver infiltration (due to a lack of the amino acid methionine), and suppression of CNS functions.
- Consequences of excess: creates a high burden on the kidneys with nitrogenous waste products (urea, creatinine), shifts the acid-base balance of the blood towards acidosis, and promotes allergies.
The optimal daily requirement is 80–120 g, with the proportion of animal-derived proteins reaching up to 55%.
Role of lipids and cholesterol
Fats are the main energy base of the body with a caloric coefficient of 9 kcal/g. Their digestibility directly depends on the melting point: liquid at room temperature and low-melting fats (margarines, butter, pork fat) are absorbed by 95–98%, whereas high-melting fats (beef, mutton) are absorbed significantly worse.
A special role is played by essential polyunsaturated fatty acids (PUFAs) found in vegetable oils, and phospholipids (e.g., lecithin), which protect the liver from fatty degeneration.
The most important sterol is cholesterol. It is necessary for the synthesis of steroid hormones and bile acids. The daily physiological norm is 300 mg. It cannot be completely excluded from the diet: a deficiency of exogenous cholesterol stimulates its internal synthesis and threatens the development of immunodeficiency. Lipoproteins transport cholesterol in the blood; low-density (LDL) and very low-density (VLDL) fractions tend to break down and deposit cholesterol on blood vessel walls, triggering the pathogenesis of atherosclerosis.
Physiological standards (SanPiN 2.3.2.1078-01)
Reference indicators are used to control organized nutrition. The average daily human energy requirement is set at 2500 kcal.
| Nutrient | Daily requirement |
|---|---|
| Proteins | 75 g |
| Fats (incl. PUFA 11 g) | 83 g |
| Digestible carbohydrates | 365 g |
| Dietary fiber | 30 g |
| Vitamin C | 70 mg |
Nutrition control in groups is carried out by calculation methods (using menu breakdowns), laboratory methods (assessment of the actual caloric content of dish samples), and through dynamic observation of body weight.
Briefly: answers to topical questions
What functions does cholesterol perform in the human body?
Cholesterol performs plastic, metabolic (hormonal), and digestive functions in the human body.
- Plastic function — participates in the formation and synthesis of cell membranes.
- Metabolic (hormonal) function — serves as a precursor for steroid hormones (including vitamin D).
- Digestive function — is used for the synthesis of bile acids, which are necessary for the emulsification and absorption of fats in the intestine.
What methods exist for assessing a person's nutritional status?
Assessment of a person's nutritional status is carried out using anthropometric and laboratory methods that determine the state of the body's protein pools.
- Anthropometric methods — are used to assess somatic muscle protein by measuring mid-upper arm muscle circumference (MAMC), and also include measuring body weight, height, waist circumference, and calculating the body mass index (BMI).
- Laboratory methods — are used to assess the visceral pool (blood and internal organ proteins).
Which amino acids are considered essential for an adult?
The essential amino acids that cannot be synthesized in the body and must be obtained from food include:
- Valine
- Leucine
- Isoleucine
- Methionine
- Phenylalanine
- Tryptophan
- Lysine
- Threonine
Which specific fatty acids belong to the polyunsaturated fatty acid (PUFA) complex?
The complex of polyunsaturated fatty acids (PUFAs) includes the following acids:
- Arachidonic acid — found in butter and pork fat, participates in the formation of vitamin F.
- Linoleic acid — found in vegetable oils, participates in the formation of vitamin F.
- Linolenic acid — also obtained from vegetable oils.
- Eicosapentaenoic acid (C20:5) — belongs to the ω-3 class.
- Docosapentaenoic acid (C22:5) — belongs to the ω-3 class.
By what formula is the amino acid score of dietary protein calculated?
The amino acid score of dietary protein is calculated as the percentage ratio of the amount of a specific essential amino acid in the evaluated product to the amount of the same amino acid in the standard ("ideal") protein.
Calculation formula: Amino acid score = [amino acid (mg) in 1 g of product × 100%] / [amino acid (mg) in 1 g of "ideal protein"].
This indicator is used as a criterion for the biological value of protein.
Which vitamins and minerals are regulated in the daily diet according to SanPiN, apart from vitamin C?
The daily diet regulates the following vitamins and minerals:
- Vitamins: retinol equivalent (RE), thiamine (B₁), riboflavin (B₂), niacin equivalent (NE), tocopherol equivalent (TE).
- Minerals: sodium, potassium, calcium, phosphorus, magnesium, iron.
To remember the physical activity intensity groups for healthcare workers, associate them with movement: a general practitioner sits in an office (Group I, PAL 1.4), a nurse walks around the ward (Group II, PAL 1.6), and a surgeon actively works with their hands in the operating room (Group III, PAL 1.9).
Class and exam questions
What is the specifically dynamic action of food substances?
This is the increase in metabolic rate after food intake. Proteins produce the maximum effect, while with a mixed diet, the basal metabolic rate increases by 10–12%.
Which amino acid protects the liver from fatty infiltration?
Methionine. It is involved in the endogenous synthesis of choline, which is necessary for normal lipid metabolism. The best dietary sources of methionine are cottage cheese, cheese, and milk.
What is the disadvantage of margarine as a food product?
During the production of margarine through hydrogenation, vegetable oils lose polyunsaturated fatty acids, sitosterols, and phospholipids, turning exclusively into an energy source.
What else to study on this topic
- Processes of amino acid reutilization during protein starvation, recovery, and rapid growth.
- The principle of mutual supplementation of limiting amino acids when combining foods.
- Instrumental methods for determining energy expenditure: direct and indirect calorimetry (by Douglas-Haldane).
- The effect of excess vegetable fats on thyroid function and vitamin E metabolism.
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Other topics in "Chapter 5. Ecological and hygienic problems of population nutrition"
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