1. Introduction
The question of whether specific types of diets provide health benefits is the subject of many debates and discussions. When considering the right diet, it is worth becoming acquainted with reliable information available in magazines or while surfing the Internet. This is difficult predominantly due to the generation of implausible results by nutrition researchers [
1]. Furthermore, due to many sociodemographic factors, including age, budget, access to groceries, and environmental and genetic predispositions, it is almost impossible to generate one potential list of meals that everyone should follow [
2]. Therefore, each diet should be adjusted separately for each individual depending on their nutritional needs.
It is worth noting that current literature indicates quite contradictory findings and conclusions regarding each type of diet. Undoubtedly, diet has an impact on the development of disease, but its effects are not always consistent and easy to explain. For instance, it was found that a plant-based diet plays a beneficial role in the prevention of many chronic diseases, including cardiovascular diseases [
3] and diabetes [
4]. Moreover, it was determined that plant-based meals reduce the risk factors for coronary heart diseases [
5,
6,
7] and body mass index (BMI) [
8,
9] and lower blood pressure [
10,
11]. In contrast, Phillips F. suggested that vegetarians and vegans may be at greater risk of increased plasma homocysteine levels, a rising risk factor for cardiovascular disease [
12]. In line with this, Ho-Pham et al. suggested that a plant-based diet increases the risk of low bone mineral density, which predisposes individuals to osteoporosis [
13]. Furthermore, studies indicate that a vegetarian diet may reduce the risk of certain types of cancer, such as colorectal cancer and breast cancer. For example, a study of 469 Taiwanese women found that a vegetarian diet was inversely associated with breast cancer risk (
p < 0.05) [
14]. However, the evidence regarding the impact of a vegetarian diet on cancer risk is not yet conclusive, and more research is needed in this area. Regarding the role of diet in diabetes, several studies have found that a vegetarian diet can help with the prevention of this disease. For example, a study of over 200,000 adults found that vegetarians had a 53% lower risk of developing diabetes compared to non-vegetarians [
15].
The literature is more consistent in the case of a diet containing red meat meals. For instance, Bonaccio et al. proved that consuming this type of food increases the level of crucial biomarkers of inflammation, such as C-reactive protein (CRP), interleukin-6, and fibrinogen [
16]. Furthermore, processed meat and red meat that contains many salts (sodium) are positively associated with elevated blood pressure [
17] and promote vascular stiffness [
18]. In relation to cancer, red meat is rich in carcinogens, including heterocyclic amines and polycyclic aromatic hydrocarbons, which are produced while cooking red meat at high temperatures [
19].
Due to the existing COVID-19 pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), it is important to take a closer look into different methods of diseases prevention. Undoubtedly, the COVID-19 pandemic has had an impact on almost every corner of an individual’s life. Due to the implemented social isolation and fear of COVID-19 infection, this pandemic at least indirectly impacted changing eating habits. During the highest waves of SARS-CoV-2 infection, many stores and grocery stores were closed. Therefore, due to the limited access to some food products, maintaining a proper diet that is in line with nutritional needs was a big challenge. Furthermore, the economic crisis caused by the COVID-19 pandemic led to an increase in the prices of food products, additionally hindering maintenance of a proper diet. Although COVID-19-associated mortality and morbidity are gradually decreasing [
20], some nutritional habits have remained and require improvement. Moreover, there are several pieces of evidence showing the beneficial role of diet in the prevention of COVID-19 disease. For instance, the American Diabetes Association in 2019 and Diabetes Canada in 2020 suggested that low-carbohydrate diets are positively associated with the improvement of glycemia and the reduction of medication doses for people with type 2 diabetes [
21,
22]. Since it is known that insulin resistance is one of the most important risk factors of COVID-19 severity, it is reasonable to conclude that a low-carbohydrate diet may be useful in preventing COVID-19 disease by increasing glucose levels in the patient’s blood.
Taking into account the abovementioned advantages and disadvantages of different types of diets on health conditions, we put efforts into identifying the correlation between the existing COVID-19 pandemic and the potential changes in nutritional habits among Polish inhabitants. Furthermore, we tried to answer the question of which type of diet may be useful for the prevention of chronic diseases that Polish inhabitants suffer most from. Data included in this study were generated before the COVID-19 pandemic and 2 years after the first outbreak of SARS-CoV-2 infection in December 2019 [
23] to show any potential changes in nutritional habits over time.
4. Discussion
According to the World Health Organization, noncommunicable diseases such as heart disease, stroke, cancer, diabetes, and chronic lung disease are the reason behind approximately 41 million deaths per year, which account for 71% of all deaths worldwide [
28]. This statistical percentage in Poland is not lower at all. As shown by the findings of the National Health Test of Poles 2022, approximately every third Polish inhabitant is diagnosed with hypertension, every fifth person suffers from allergies or asthma, and every sixth person develops depression [
29]. Consistently, our study shows high incidence rates of hypertension (32.33% in 2019–2020 and 34.95% in 2021–2022), COVID-19 infection (32.35% in 2021–2022), and joint disease (19.41% in 2019–2020 and 21.71% in 2021–2022). Unfortunately, these incidence rate percentages were higher in 2021–2022 than in 2019–2020, which is in line with the National Health Test Poles 2022 [
29]. Furthermore, we observed a significant correlation between the presence of the COVID-19 pandemic and increased likelihood of developing one of the analyzed chronic diseases.
Our study revealed that male respondents were more likely to develop hypertension (OR = 1.35 CI 95% (1.28–1.43),
p < 0.001,
Table 5). This result is consistent with several other studies [
30,
31,
32,
33]. However, it is worth taking into account the age of the analyzed respondents. Di Giosia et al. reported that postmenopausal women are more likely to display a rapid increase in hypertension prevalence. Several studies suggest that sex hormone changes play a crucial role in the pathophysiology of hypertension in women after menopause [
30,
31]. For instance, data from the US show a higher incidence of hypertension among male respondents until the age of 45 years. After this age, a similar rate was observed, and hypertension was more prevalent in women than in men after the age of 65 years [
31]. Furthermore, our study revealed that male respondents are more likely to suffer from diabetes (OR = 1.20 CI 95% (1.11–1.30),
p < 0.001,
Table 12). Although this finding is quite contradictory to the known literature [
34], it is worth considering other factors that increase the susceptibility to morbidity to chronic diseases, including BMI, stress level, diet, physical activity, past or current secondary diseases, etc. Nevertheless, our study shows that sex affects the probability of morbidity to different chronic diseases. However, additional studies examining the mechanisms of pathophysiology of sex differences of several chronic diseases are required.
There was a significant association between high education levels and reduced likelihood of suffering from almost all of the analyzed diseases (we did not see this correlation only with COPD, allergies and asthma, and COVID-19 disease). This finding shows the significant role of awareness in the prevention of common diseases. Furthermore, as documented by Cutler and lleras-Muney, individuals with higher education levels obtained more flu shots, vaccines, mammograms, Pap smears, and colonoscopies [
35]; the earlier a disease is detected, the greater the chance of survival. Therefore, clinical healthcare professionals and several laws should initiate health promotion strategies to increase the attention and awareness among people [
36].
The specific impact of different diets on preventing SARS-CoV-2 infection and the overall management of COVID-19 disease remains a debatable and scarce topic of research. This study aimed to investigate the potential beneficial roles of various diet types in the prevention of common 21st-century diseases, including COVID-19, as well as to explore the association between the existence of the COVID-19 pandemic and potential changes in nutritional habits among the Polish population. We found a significant association between the consumption of meals according to the food pyramid and decreased likelihood of developing hypertension (
Table 5), COVID-19 disease (
Table 6), joint disease (
Table 8), depression (
Table 9), heart disease (
Table 10), and neurological diseases (
Table 11). This finding means that diet plays a role in preventing these diseases [
37].
A study conducted by Franco et al. analyzed the impact of COVID-19 confinement on physical activity and Mediterranean diet adherence among employees participating in a Healthy Cities program in Spain [
38]. The results showed increased sedentary behavior but also higher levels of physical activity and greater adherence to the Mediterranean diet during the pandemic, suggesting a positive effect of remote work on health-promotion efforts among this population.
In another systematic review that examined changes in eating behavior during the COVID-19 pandemic by comparing behaviors before and after its outbreak, the findings revealed shifts towards increased snack frequency, a preference for sweets and ultra-processed foods over fruits and vegetables, and higher alcohol consumption across different countries [
39]. Consequently, adherence to healthy diets decreased, emphasizing the importance of considering these findings for future policies and strategies during similar alarming situations like the COVID-19 pandemic.
Proper nutrition has long been recognized as a key factor in preventing various diseases and alleviating their symptoms. There is mounting evidence that suggests that a vegetarian diet can have a significant impact on disease prevention. Studies indicate that a vegetarian diet may reduce the risk of certain types of cancer, such as colorectal cancer and breast cancer. Another study found that a vegetarian diet was associated with better glycemic control in individuals with type 2 diabetes [
15]. In addition to the above, a vegetarian diet has also been associated with a lower risk of obesity, hypertension, and chronic kidney disease [
40,
41,
42]. It is thought that the high fiber and low fat content of a vegetarian diet may contribute to these health benefits. A systematic review and meta-analysis of nine studies found that individuals who followed a plant-based diet had a lower risk of developing type 2 diabetes compared to individuals who did not follow this kind of diet [
43]. A more recent systematic review and meta-analysis of 11 studies found that individuals with type 2 diabetes who followed a vegetarian diet for at least 12 weeks had decreased body weight and improved glycemia [
44]. These findings suggest that a vegetarian diet may be effective in preventing type 2 diabetes. Consistently, our study revealed the significant association between the consumption of a plant-based diet and decreased likelihood of developing hypertension (
Table 5), diabetes (
Table 12), and neurological diseases (
Table 11). In line with these results, hypertension was less common among respondents who declared that they consumed meat meals (
Table 5). Furthermore, our study found that respondents with a plant-based diet were more likely to have depression symptoms (
Table 9). This finding is in line with the study by Jain et al. who reviewed data from 23 studies, including 25 study outcomes. Most of the studies (44%) proved a significant association with higher rates of depression; seven outcomes (28%) showed a beneficial role of this diet on depression. The other seven outcomes revealed no correlation in this regard. These pieces of evidence demonstrate contradictory results, possibly due to the heterogeneity of the studies analyzed [
45].
Interestingly, our study shows a significant correlation between a decreased risk of COVID-19 infection and the consumption of reduced-sodium meals (
Table 6). To the best of our knowledge, there is no study describing this association between this particular type of diet and the prevalence of COVID-19 infection. Therefore, this sheds new light in the scientific world that we believe is worth investigating in detail. Sodium plays a crucial role in the regulation of electrolytic balance and the expression of ACE in SARS-CoV-2. As Luo et al. and Lippi et al. found, sodium concentration is lowered in COVID-19 patients and decreases in line with the severity of the disease [
46,
47]. In contrast, Cure et al. proved that COVID-19 infection may increase the risk of hyperglycemia through the glucose regulation by the Na+/H+ exchanger and lactate pathways. During COVID-19 infection, the activated angiotensin II contributes to insulin resistance and leads to hypoxia and extracellular acidification. The consequence of this mechanism is the accumulation of calcium and sodium ions in the cells and the production of reactive oxygen species, which damage pancreatic tissues [
48].
The present study is subject to several notable limitations. Initially, the reliance on an online survey as the primary data collection method introduces potential concerns regarding the authenticity of participant responses. The absence of direct oversight makes it challenging to ascertain the accuracy and sincerity of the information provided by respondents. These concerns refer to self-reported sociodemographic data, diagnosis of chronic diseases, and diet. Moreover, the extent of incompleteness or dropout rates at different stages of the research remains uncertain, thus potentially impacting the overall quality and reliability of the collected data. Additionally, the investigation’s focus on food preferences lacks a critical analysis of the caloric content of the diets consumed by participants, rendering the impact of dietary choices on the outcomes less comprehensive. This omission is particularly significant, as differences in metabolism between genders could yield disparate physiological responses to diet, thus introducing a potential confounding variable that may have affected the study’s conclusions.