Introduction

Today, there is a difficult global epidemiological situation due to spread of the novel coronavirus infection COVID-19. Countries take a number of sanitary-epidemiological and social measures to prevent the infection spread, from closure of social institutions and restaurants to transfer of schoolchildren and students to remote learning [1-3]. Numerous studies indicate that any precarious situation (changes in daily routine, dietary pattern, mode of study; the pandemic) may result in exertion of adaptation mechanisms and decline in children's functional capabilities [4-8]. Currently, adults must clearly understand that the immune response to infection would be determined by the family meal patterns and by the diet quality. After all, healthy diet has a complex protective impact on physical well-being. It underpins human vital activities ensuring optimal functioning of all bodily processes [9]. Achieving a perfectly healthy diet in adults and children is still a topical issue in our country. However, the other risk factors associated with quarantine measures cannot be excluded, such as uncontrolled access of children to information and communication technologies, diet violations in secondary school students, and insufficient physical activity. Nutrition remains a major environmental factor affecting the body's resistance to harmful environmental conditions [10, 11]. Rational nutrition and balanced diet during the pandemic of the novel coronavirus infection COVID-19 provide the human body with essential vitamins and minerals. It has been found that vitamins А, С, D, Е, В₂, В₆ and В₁₂, folic acid, iron, selenium and zinc are essential to ensure the body’s immunocompetence [12-15]. The foreign and national studies show that inadequate essential micronutrient supply results in reduced function of immunocompetent organs, as well as in the increased risk of infection and complications. During the pandemic, children must be provided with dietary protection against harmful environmental conditions by means of achieving safe and balanced diet at home based on the child’s age-associated physiological needs.

To assess actual dietary intake in secondary school students during remote learning due to COVID-19 quarantine and restrictive measures.

Fifth- and sixth-grade secondary school students aged 12-13 studying in secondary general education institutions (n=40: 18 boys and 22 girls) were enrolled, who lived in different cities of Kemerovo region, and whose parents had approved their participation in the study. The randomly selected children were assessed individually at home in the presence of one of the parents using Zoom platform in October 2020. The novel coronavirus infection epidemiological features were the reason to use the Zoom platform. Inclusion criteria: age peculiarities, belonging to a Slavic ethnic group, remote learning for at least a week, existence of scales for weighting dishes or food products at home; one of the parents staying at home during the day. Children, who showed signs of acute respiratory disease during the survey period, were excluded from the sample.

Actual dietary intake of the children staying at home was assessed using the 24-hour dietary recall (24HR). The questionnaire was completed throughout the week. The rules for completing the children’s food diaries were previously explained to parents, the “Album of Food Portion Sizes” allowing one to determine the size of food portions consumed by children was distributed [16].

The nutritional and biological value of the children’s diet was evaluated in accordance with the existing regulations [17, 18]. In addition, the loss of nutrients during thermal food processing was taken into account. The consumed set of food products was compared with the set recommended by the Federal Research Centre of Nutrition, Biotechnology and Food Safety to children staying at home because of self-isolation or quarantine due to COVID-19 [19]. Statistical processing of the results was performed using the Statistica 6.0 software package based on the data distribution through calculation of the analyzed indicators’ statistical characteristics (Ме – median, 25; 75^th percentile – interquartile range); р < 0.05 was considered to be statistically significant.

Self-isolation and quarantine measures due to global pandemic of COVID-19 modified the daily routine in both adults and school-age children. When staying at home with their children, the parents had to plan the food purchase carefully, preferably for a long time. At the same time, they had to create a meal plan, and to follow the family dietary pattern. The enforcement of children’s self-isolation affects their level of physical activity. The latter decreases significantly relative to physiological needs in moving, and, as a consequence, results in energy consumption reduction by 200-400 kcal/day and more in children aged 3–18 [18]. However, parents do not take this fact into consideration; the meal plan is created based on the family dietary habits.

Regardless of the epidemiological situation, the child’s diet should include all traditional food products. The study results showed that the daily average food product set and the children’s food intake during quarantine and self-isolation were not optimal. Comparison of food product set calculations for the children’s diet is presented in tab. 1.

Stereotypes toward eating behavior are developed in families. Both the choice between various food products and food preparation are directly influenced by parents. Analysis of the food product set during the pandemic revealed problems of various food products consumption, typical for many Russian families [4–6]. Overconsumption of pasta (by 140% of the recommended dietary allowance), cereal grains and legumes (by 28%), sausage products (by 173%), confectionery products (by 64%), and sugar (by 68%) was detected in children during self-isolation. Access to food products and the presence of spare time allowed the children to make extra breaks for snacks (sandwiches, cookies, slices, gingerbread, etc.). Furthermore, the wait time between meals was reduced to 2.5–3 hours.

It is noteworthy that regardless of the recommended sausage products and sugar intake reduction during self-isolation, the average daily intake of those still exceeded the recommended dietary allowance by 2.7–3.2 times and 1.6-1.8 times respectively. Regardless of the epidemiological situation, the insufficient use of such food products as fish at home was detected. In the secondary school students, the fish consumption was reduced to 52-68% of RDA.

As we can see, the preference of poultry dishes had been shaped in children. The poultry intake exceeded the recommended daily allowance by 30–36%/day. Consumption of cottage cheese reduced by 15% of recommended daily allowance, eggs by 45%, and juices by 40% was detected.

Gastrointestinal tract is one of the most active microbial ecosystem of the body playing a vital part in immunological status. Therefore, probiotics, both contained in fermented dairy products and vegetables, fruit, cereal grains, would boost the child’s immunity. However, it has been shown that the diet of the child staying at home is characterized by reduced intake of milk and fermented dairy products (by 26% of RDA), vegetables (by 27%), and fruit (by 30%).

The children’s food intake analysis results are consistent with the previous studies conducted in the other regions of the country.

By the time of entering secondary school, the students’ dietary habits have been already shaped. During self-isolation, cooking of main dishes and pastry is the most common, the intermediate goods (dumplings, Russian ravioli) are widely used. It has been found, that secondary school students do not limit themselves when choosing dishes and food products. They consume foods in accordance with the already shaped family dietary habits. Secondary school students also consume items not recommended to children of their age (mayonnaise dressing, ketchup, deep-fried buns, roasted potatoes, various spicy seasonings).

Nutritional diversity (adequate levels of main nutrients, dietary fiber, vitamins and minerals consumption) is the basis of the rational protective diet. Numerical values describing energy consumption and nutrient intake in children are presented in tab. 2.

Due to reduced physical activity during self-isolation, the Federal Research Centre of Nutrition, Biotechnology and Food Safety recommended to reduce the daily calorie intake both in adults and children. In spite of the fact that physiological requirements (PR) of secondary school students allow for daily calorie intake of 2400 kcal/day, during self-isolation the children aged 7–18 are recommended to consume 1600–2000 kcal/day. Based on the energy value, the actual daily average food intake did not exceed the PR. However, recommendations were not adopted; in the context of children’s physical inactivity the energy value of the diet exceeded the values recommended to children self-isolating at home during quarantine by 18–47%. Distribution of percentiles for a number of micronutrient intake values showed that significant (in terms of children’s health) protein and animal protein content of the diet was within the normal range (95-105%).

It should be noted that excessive amount of such foods as sausage products and mayonnaise dressing in the children’s diet results in predominance of fats in the food. The fat content of the daily diet exceeded physiological requirements by 1.1–1.3 times. At the same time, compared to normal consumption of carbohydrates (96% of PR/day), the intake of mono- and disaccharides in children exceeded the recommended dietary allowance by 33–49% of PR. Reduced dietary fiber intake was revealed, the content of dietary fiber varied between 68-93% of daily dietary allowance. The daily average consumption of protein, fat and carbohydrates was unbalanced (1:1.2:4.7).

Analysis of vitamin and mineral intake with food showed that the lowest daily average intake values were obtained for vitamin В₁ (69% of PR), vitamin В₂ (73% of daily dietary allowance), and vitamin РР (niacin) (85% of PR). The intake of vitamins А (expressed in terms of retinol equivalents) and C was within the range of physiological needs. Analysis of mineral intake revealed reduced intake of calcium (to 35–46% of daily requirements) in secondary school students, along with excessive intake of sodium (the sodium level was elevated by 2 times on average). Adequate intake of phosphorus, magnesium and iron with food was detected. Normal absorption of calcium requires rational ratio to phosphorus, however, the level of phosphorus in foods consumed by children was 1.8 times higher than required. That reduced availability of calcium for absorption in the child’s body.

DISCUSSION

The diet composition in secondary school students, forced to stay at home because of self-isolation due to COVID-19 and studying remotely, can be characterized as not optimal and not rational. According to the Federal Research Centre of Nutrition, Biotechnology and Food Safety guidelines, during the long-term homestay, the energy requirements should be reduced by means of reduced intake of some food products. During self-isolation, the insufficient physical activity is considered a risk factor for weight gain, as well as for impaired motor and evacuation function of the gastrointestinal tract.

However, due to access to food and presence of spare time in secondary school students, as well as to lack of set daily routine, and frequent breaks for snacks, the daily energy value of the food consumed was excessive; the nutrient composition of the food was unbalanced, since the children’s dietary habits had not changed [11]. Regardless of the fact that protein and carbohydrate intake (absolute values) was close to normal, the fat intake was excessive. Analysis of vitamin and mineral intake in secondary school students revealed reduced absolute content of vitamins В₁, В₂, and calcium, along with excessive intake of sodium. This is in line with the results of previous studies carried out in other regions of the country during the period of epidemiological well-being. Results of a number of studies show that carbohydrate and fat rich dietary pattern is shaped in the modern secondary school students [20 21]. Analysis of foreign literature also provides evidence of health problems in foreign children due to malnutrition, eating disorders, etc. [22, 23]. The revealed imbalance of macro- and micronutrients is associated with insufficient intake of specific food groups. Thus, during self-isolation, the secondary school students have not managed to reduce the intake of salt, sugar, saturated and trans fatty acids at expense of the food products being the main source if those (bakery products, sweet sparkling drinks, nectars, various sausages, cheese with fat contents exceeding 30%, mayonnaise, etc.) [19]. The secondary school students’ daily diet included excessive amount of sausage products (by 2.1 times), confectionery products and sugar (by 1.6 times), pasta (by 2.4 times), bakery products (by 1.2 times). The diet was extremely scarce in terms of the amount of fish and seafood, eggs, milk and dairy products, vegetables, fruit, and juices. The secondary school students did not follow one of the major principles of rational nutrition, such as daily routine of eating. Parents paid little attention to menu planning based on the children’s age peculiarities. Adjusting the supply of vitamins and minerals only through cooking traditional dishes and culinary display does not work.

Analysis of actual dietary intake in modern secondary school students, especially during the pandemic, remains of key importance, since the analysis results reflect home meal planning in families, as well as the impact of the regional socio-economic situation. The study results showed that the secondary school students’ diet during self-isolation at home was not optimal. The imbalance of macro- and micronutrient intake is associated with imbalanced food product set: excessive intake of high-fat foods, sugar, and confectionery products along with insufficient intake of fish, dairy products, vegetables, and fruit. Eating pattern and dietary habits of the family depend on the parents’ education on nutrition, which should be taken into account when developing guidelines on optimizing nutrition. In order to adjust micronutrient composition of the secondary school students’ diet, it is necessary to include specific food products, nutritional supplements, as well as complexes of vitamins and minerals boosting body’s immune resistance during the pandemic.