The average lifespan has increased in the past few decades due to socioeconomic and health-related development. As a result, it has led to a higher prevalence of chronic old-age diseases such as diabetes, obesity, cardiovascular diseases and cancer. Many of these diseases are conditioned by the modifiable risk factors including smoking, physical activity, alcohol intake, body weight and diet (1). Thereupon, changing and maintaining favorable lifestyle behaviors as early as possible in people’s lives are a key strategy for good health and longevity.

Leading a healthy lifestyle may be challenging under psychological stress, which is very prevalent contemporarily. Under psychological stress, attention is redirected to stressor-related issues and dietary behaviors may be neglected (2). In particular, undergraduate students face multiple psychological stressors that may negatively affect their health behaviors (3). Recently, the general stress associated with academic workload has been further exacerbated by the COVID-19 pandemic and global lockdown (4); distancing from family members and friends, thereby diminished social interaction and emotional support together with new online teaching and assessment methods, which required appropriate digital infrastructure and skillset, have led to unprecedented psychosocial burden (5, 6). The emergent problems appeared to heterogeneously affect health-related behaviors (7), which, in turn, could depend on some personal factors (8).

Personality refers to individual differences in characteristic patterns of thinking and is one of the most significant aspects of human life. It has an influence on all human behaviors in both personal and social life (9). Personality development is a complex process influenced by factors such as genetics, environmental factors and temperament which is a precursor of the structure of personality (10). Personality traits may have an impact on propensity to change and maintain favorable lifestyle habits. This issue has been raised by multiple studies to highlight the link between personality traits and the tendency to consume specific food groups (11). In particular, neuroticism was associated with unhealthy diet habits such as low consumption of fruits and vegetables, and higher consumption of sugar and saturated fats (11). On the other hand, conscientiousness was found to be linked with higher scores on the health aware diet factor and higher intake of fruits and vegetables (11–13). Even though similar studies have already been conducted, none of them focused specifically on a population under severe psychological stress. In fact, the recent meta-analysis on this topic showed that further research is required to explore this relationship in more vulnerable groups (11).

The primary aim of the present study was to investigate the link between personality traits and dietary intake of specific food products in medical students facing a stressful subject examination in the first COVID-19-related lockdown. In addition, the other health-related measures (general quality of diet, physical activity, body-mass index and cigarette use) were also assessed as secondary outcomes in terms of their relationship to personality traits.

The association between personality traits and health-related behavior has been a subject of many studies (12, 13, 31–35). Nevertheless, the recent systematic review on this topic indicated the need for further investigation involving particular populations (11). Due to overwhelming psychological stress experienced in everyday live (the COVID-19 pandemic, the war waged nearby), it was particularly interesting to assess this relationship in a severely stressed population. Our data indicated that higher conscientiousness may help in leading a generally healthier lifestyle in this population. Such association – although in line with many previous studies (34, 36–38) – is particularly interesting, as the studied population of medical students presented relatively high background level of conscientiousness; we found no ceiling effect in this regard. Even though conscientiousness was found to be positively associated with eating healthy food, there was no reverse dependency between conscientiousness and consumption of less healthy products.

Our findings are in line with the existing body of literature, despite the specific type of the population examined. The study performed among South Korean college students described a positive correlation between conscientiousness and extensive self-reported physical activity and lower BMI, which may be indicative of a healthier lifestyle (31). Another study carried out among patients with metabolic syndrome in Poland suggested an association between low conscientiousness and the tendency to develop metabolic syndrome which may be diet-induced (32). The role of conscientiousness in terms of health-related measures was also taken into consideration in a study on child obesity, where a positive correlation between higher conscientiousness and lower BMI was demonstrated. Additionally, the participants with a stronger expression of this personality trait had a tendency to engage more in physical activity and paid attention to their diet in terms of ingredients and regular meal rhythms (33). Furthermore, the study performed in a large sample of adult Estonians also found the link between higher conscientiousness and health-aware diet (13). A specific population of 70-year-olds also demonstrated higher conscientiousness correlated with a more favorable diet and lower BMI (35). From a different perspective, another study conducted among young adults showed an association between higher conscientiousness and greater plant-food consumption (12). It all means that the phenomenon of conscientiousness predisposing to healthier habits is very versatile and works under various circumstances.

Conscientiousness is defined as a personality trait that reflects tendencies to be hardworking, rule-following, determined and task-oriented, set on planning and achieving goals (39). It is also described as a foundation of self-discipline and the basis for regulation of internal urges, which may function as a source of control over health-related behaviors (32). This personality construct may even be a vital determinant of positive aging and general human capital (40). In this light, it becomes clear why conscientiousness, not other personality indices, predicts more favorable health behaviors. In general, medical students who were examined in this study are knowledgeable about healthy diet. However, their behavior does not necessarily reflect the knowledge. This phenomenon, referred to as the knowledge–behavior gap, may be less pronounced in highly conscientious people, particularly in an unusual context, such as examination session (41).

As high conscientiousness can lead to development of more favorable health behaviors, people with low conscientiousness may require special attention. First of all, it is important to note that people with lower conscientiousness are not devoid of this quality, it is simply weaker. Therefore, they are less likely to follow through with plans and are less motivated to achieve their goals (42). That is why it could be intriguing to explore whether personality may be modified. Although classically regarded as stable, personality traits can evolve and may be modified with specific interventions, as suggested by evidence presented in the literature (43). The possibility of personality modification is particularly the case in young adults, whose development is still in progress (44). Individuals with low conscientiousness should attempt to modify their lifestyle by introducing mechanisms that may not only improve conscientiousness attributes but also contribute to more effective stress management and a greater awareness when planning a diet. The most well-known and effective method that develops conscientiousness is the behavioral activation method (43). Applying this approach, an individual monitors his/her habits and behaviors on a daily basis and defines them in terms of importance – duty or pleasure. A person learns the structure of their day and is able to define the activities that they consider pleasurable or obligatory. Someone who is not good at planning or organization, through systematic work on learning the schedule of the day, observing at what times of the day and night they function better or perform activities more efficiently, will eventually be able to effectively manage not only their functioning, but also their diet.

When an individual does not plan to modify his or her own personality traits, e.g., conscientiousness, but wishes to improve diet, attention should be paid to issues such as self-regulation and adherence to nutritional standards (45). The ability to self-regulate is recognized by researchers as an element specific to the human race, one that distinguishes us from other species. Self-regulation is nothing other than the ability to change one’s own feelings, thoughts and actions. Thanks to it, individuals are capable of inhibiting, e.g., the process of gratification which can negatively affect our diet. By learning about the three stages of self-regulation, namely a sense of duty toward nutritional standards, observation of one’s own habits, and the ability to change one’s behavior when it is not in accordance with the standards, one can improve daily diet (45). Food standards are the norms, patterns, values or expectations that guide an individual in the process of self-regulation. The greater the commitment and loyalty to one’s own set objectives, the better an individual can expect to do when starting a healthy diet. An equally important aspect is self-efficacy (46) – the greater the belief in one’s own abilities, the easier it is to achieve a goal. It is important to note, however, that the nutritional patterns we follow are also socially and culturally conditioned (45). It is worth paying attention to the characteristics of stimuli associated with general diet that reach us. We should analyze how we re-late to them, and how strongly they construct our lifestyle.

Apart from conscientiousness, the literature reports the connection between neuroticism and the tendency to consume unhealthy diet (47–50). It is manifested by a preference for sugar-containing products (sweets, chocolate, and soft drinks) (47–49). A few of the studies also found the association between higher neuroticism and increased salty food intake, along with reduced fish and vegetables consumption (47, 50). Our results did not confirm the link between neuroticism and unhealthy habits, however, this might have been a false-negative effect as some p-values for this link were relatively low. Especially the association between neuroticism and BMI presents some but inconclusive trend. This uncertain outcome might be a result of the fact that BMI of great majority of the participants falls within the normal range, hence the low variance and lack of discrimination of this feature by personality traits was observed. It is also worth noting that considering all the stressors reflected in high degree of anxiety and depression symptoms, the studied population appeared to collectively present “neurotic behavior,” which might stifle potential dependencies involving this personality trait.

As for sociodemographic factors, among the surveyed students, there was an association found between sex and the products consumed. Men more often included such products as red and white meat, eggs, light bread and potatoes in their diet. Women, on the other hand, consumed more vegetables, fruits and nuts. These results are consistent with those obtained in other studies (51, 52) suggesting that men consume more animal-derived and fatty meals and are less likely to become vegetarians, whereas women present a greater engagement in healthy nutrition. This difference may also simply result from higher energy demand in males (30). Additionally, our results showed a positive correlation between the size of the place of residence of the family of origin and the products consumed or the lifestyle. Students coming from larger cities consumed more vegetables, fish and seafood, and paid more attention to physical activity. This may be intriguing and counterintuitive, however, it finds some confirmation in the other study linking the residence in rural areas with greater consumption of fats and oils than that observed in bigger cities (53).

The present study has several limitations. Firstly, to a large degree it is a secondary analysis of an existing database – a participant subsample has been already described with regard to consumption of fermented food and mental health in previous papers (14, 15). As such, the certainty of the reported findings may be diminished and the choice of specific food groups included in the questionnaire was dictated by the requirements of that primary study. Moreover, the sample size is relatively small for detecting weaker associations between personality traits and behavior. Secondly, personality traits were assessed based on a shortened version of a questionnaire (Big Five Inventory-Short), which relies on three items for each personality trait only. Nevertheless, the questionnaire assures its validity (18, 19). The internal consistency measures were deemed acceptable for most personality traits (54) with the exemption of Agreeableness for which Cronbach’s alpha was impaired; in consequence the results for Agreeableness should be regarded with caution. Thirdly, our Food Record questionnaire neither includes all the food groups (e.g., data on consumption of sweets, coffee, alcohol and drugs was not collected, which might affect the consumption of products with low nutritional value), nor evaluates the ways in which the meals were prepared; however, the Food Record measure was additionally validated to assure its high accuracy. Moreover, we did not examine students’ inhabiting conditions – whether they live with their parents, with roommates or on their own, which might have an impact on their daily dietary choices. Finally, the study is based on self-reported data (in particular physical activity might have been collected through accelerometers), and therefore may be more declarative and socially desirable.

Severely stressed medical students showing high conscientiousness tend to present healthier behaviors expressed as dietary patterns (more consumption of vegetables, wholegrain products, fruits and nuts) and avoiding cigarette smoking. The results are consistent with literature reports on other populations, which may suggest high versatility of the phenomenon, even in the population of high background conscientiousness. Interventions aimed at improving lifestyle habits in students with lower conscientiousness might be useful.

The dataset for this article is not publicly available due to concerns regarding participant anonymity. Requests to access the dataset should be directed to the corresponding author.

The studies involving humans were approved by Bioethics Committee of the Medical University of Lodz, Poland. The studies were conducted in accordance with the local legislation and institutional requirements. The participants provided their written informed consent to participate in this study.

JT: Conceptualization, Data curation, Formal analysis, Validation, Visualization, Writing – original draft, Writing – review & editing. AK: Writing – original draft. JK: Writing – original draft. EK: Funding acquisition, Validation, Writing – review & editing. MK: Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Supervision, Validation, Visualization, Writing – review & editing.