Dietary habits are a major aspect of people's lifestyles that influence health, morbidity, and mortality for a range of conditions. Hence, patterns of food consumption and their relation to mental health have received some attention in research [1]. For example, some observational and experimental studies explored the effects of carbohydrate intake on mood [2–4]. Other studies have assessed the association between stress and food selection, reporting partly conflicting results [5–11]. Carbohydrate consumption has been hypothesized to relieve depressive moods [12], and this has been considered as part of the causal link for developing obesity [13, 14]. However, the association has also been seen in the opposite direction, with stress and depressive symptoms resulting in poorer food choices [15]. Indeed, studies on the effects of stress on food choice show that people experiencing periods of stress reported overeating foods they would normally avoid, and that they ate these foods to feel better [16].

In children, stress was correlated with being overweight [17, 18], unhealthy eating behaviours, as well as with the use of eating as a coping mechanism [19]. For adolescents of both genders in the U.S., the lack of a healthy diet was associated with reporting depression/stress for 10 or more days in the past month [20]. Stress not only increased food consumption in certain individuals but also shifted their food choices from lower fat to higher fat foods [16].

Whilst eating has been theorized as a coping strategy for stressful situations [19], less is known about the association of stress or depression with the frequency of consumption of various food groups among college students [15]. For instance in Germany, students preparing for exams had higher stress and more tendency to eat in order to distract themselves from stress than compared to control students [21]. In the U.S., weight gain in college women was negatively associated with students being stress-free, eating vegetables, and consuming less high-cholesterol foods [22]. Additionally, given that 65% of United Arab Emirates university students reported that their stress levels were too high and 50% reported that their diet was unhealthy [23], the importance of understanding students' patterns of consumption of food groups becomes evident. If poor nutritional habits are associated with stress and/or depressive symptoms, programs addressing mental health may also lead to the consumption of healthier foods and/or vice-versa.

Although depression is often related to appetite changes [24], little research has been done to examine the relationship between healthy eating and depressed mood [25]. In fact, until recently, no studies had examined the relationship between depression and nutritional intake, e.g., among adolescents [25]. Previous studies that examined this link usually focused on single countries, e.g., the U.S. [25, 26], the UK [27], or China [15]. When single countries are examined, participants usually share the same underlying nutritional habits and other background characteristics that are potentially related to perceived stress or depressive symptoms. Single-country studies are also rarely directly comparable to one another due to the differences in measures of food consumption or mental health indicators. This has led to suggestions that future research on nutrition and on the correlation between depression and food consumption should be conducted across diverse student populations [15]. University students are particularly important as they have greater freedom and control over their lifestyles, and health behaviours formed during young adulthood may have sustaining impacts on health throughout later life [28]. Hence, it is of interest to assess the extent of association between indicators of mental health (such as perceived stress and depressive symptoms) and nutritional habits.

The aim of the analysis described in this paper is to assess the associations between mental health and nutritional habits across culturally diverse samples of students from three European countries. The analysis explores the links between reported levels of perceived stress and depressive symptoms and the consumption of selected food groups. The three samples consisted solely of first-year university students in each of the three countries; hence, sources of variability, such as education level or socio-economic status, are reduced.

Today's college students are tomorrow's parents, role models, and patients. Unhealthy food practices and habits could impose health risks later in life and could be passed on to the next generation. Diet has an effect on mood [43], and although the emotional well being of university students has been studied [44], recent reports indicate that depressive symptoms in students are of principal importance and require further study [45]. Our findings show that the relationships between food consumption and depressive symptoms and perceived stress were consistent across the studied countries but different by gender. While in males there was no association between consumption of food groups and the above-mentioned mental health indicators, the associations were quite strong in female students.

We found associations between the consumption of sweets/fast food and fruits/vegetables and perceived stress and between the consumption of fruits/vegetables and meat and depressive symptoms. The association between higher consumption of sweets and higher perceived stress levels was also reported by others: sweets, chocolate, cake, and biscuits were eaten more often under stress [8, 46]. Food composition (e.g., high fat/energy content) may influence people's selections of certain foods during life events that are stressful [46]). On the other hand, stress might trigger a loss of control mechanisms by which people avert themselves from consuming perceived fattening or unhealthy foods [16]. That "meal-type" foods, which often consist of salads or vegetables, are also eaten less frequently during periods of stress [8] might explain the observed negative correlation between fruits/vegetables and perceived stress.

Higher consumption of fruits/vegetables was associated lower levels of depressive symptoms among females in our study. The direction of this association seems to be due to the behavioural consequences of higher depressive symptoms and is consistent with the correlation between depressive symptoms and perceived stress [31]. Interestingly, more frequent meat consumption was associated with lower levels of depressive symptoms in females. The interpretation of this finding is not entirely clear. Possibly, again the consumption of meat indicates better mood, rather than that meat positively affects mood.

Conversely, fish consumption (rich in omega-3 fatty acids) might be causally associated with mood stabilization [47], with some evidence that levels of these fatty acids are linked to depression [48]. However, we did not find any association between fish consumption and depressive symptoms, consistent with Hakkarainen et al [49] who reported that dietary intake of omega-3 fatty acids showed no association with low mood level. Indeed, the evidence base on the relationships between fish consumption and depressive symptoms remains inconclusive. For instance Hakkarainen et al [50] found that subjects reporting anxiety or depressed mood had higher intake of omega-3 and omega-6 fatty acids – findings that conflict with previous reports of the beneficial effects of these fatty acids on mood, where lower prevalence of depressive symptoms was reported among people consuming high amounts of fish [51, 52]. These conflicting findings probably reflect the different dietary intake levels of omega-3 fatty acids employed in different trials (ranging from 9.6 g/day, [47] to 2.2 g/day, [49]), and the lack of distinction between consumption of white versus fatty fish, which have varying contents of fatty acids (0.48 g/100 g in white fish (cod) to 5.33 g/100 g in fatty fish (mackerel) [53].

While an increased consumption of sweets/fast food was associated with higher levels of perceived stress, the absence of this correlation for depressive symptoms might indicate that increased consumption partly relieves depressive symptoms. Carbohydrate ingestion has been hypothesized to relieve depressive moods [12], but such effects could be mediated through psychological factors rather than nutrient content of sweets [54]. Hence future studies of the influence of carbohydrates on mood will need to consider people's pre-existing psychological and physiological functioning [2].

All the above findings were observed only in women. In males, none of the associations were significant and most of the estimates were closer to zero. The single exception was increased stress and depressive symptoms in Polish males with a more frequent fast food consumption observed in univariable analysis. Since the effect was restricted solely to Polish male students and not seen for male students in the other countries, and we are not aware of any theoretical justification, we see this as a chance finding. The association disappeared in multivariable analysis using the subscale for carbohydrate dense foods. Previous studies assessing the association of food intake with one or both mental health indicators in Chinese [15] and American [15] populations did not investigate the potential effect modification by gender, therefore the global associations they observed might have also resulted from associations limited to women only. Many individual, social, and political factors influence food selection and eating patterns [55]. Hence, gender differences may result from different responses to perceived stress with respect to food consumption: either increased (hyperphagia) or decreased (hypophagia) and different prevalences of these responses by gender [8]. Females, being more often restrained eaters [56], might react more strongly to perceived stress and/or depressive symptoms in their food intake. The preparation of healthy items (salads and cooked vegetables) might also require some additional efforts. Therefore under stress or decreased motivation due to depressive symptoms their consumption might decrease. Other explanations include female perceptions of self- and body-image and self-esteem, which have been associated with depression and might be associated with food consumption [57, 58].

Using data from three European countries from a study with a common methodology, we showed an association between mental health indicators (perceived stress and depressive symptoms) and food intake in female, but not male, students. Our findings suggest that interventions oriented towards perceived stress and depressive symptoms in female students should also address the issue of healthy nutrition. Additionally, efforts to reduce depressive symptoms and stress among female students may lead to the consumption of healthier foods and/or vice-versa.