Depression is related to dietary diversity score in women: a cross-sectional study from a developing country

We observed an inverse association between DDS and severe depression, which remained significant after adjustment for confounders. However, there was no significant association between DDS and stress. To our knowledge, there is no report of the relationship between DDS and depression and stress.

Recent studies have mainly focused on the relationship between nutrients and dietary patterns and depression and stress. One study showed an inverse relationship between depression and a healthy dietary pattern with high consumption of vegetables, fruits, nuts, legumes, olive oil, fish, and low consumption of meat and meat products [4]. In another study on Australian women, a traditional dietary pattern (characterized by vegetables, fruit, meat, fish, and whole grains) was associated with lower risk of depression and the Western dietary pattern (characterized by processed or fried foods, refined grains, and sugary products) was associated with a higher risk of depression [27]. In addition, a healthy dietary pattern is inversely related to depression [28, 29]. However, the result of a meta-analysis showed no association between Western dietary pattern and depression [30].

Based on the results of the current study, an increased DDS was associated with a higher percentage of individuals who consumed food groups such as milk and dairy products, vitamin A-rich fruits and vegetables, dark green leafy vegetables, eggs, legumes, nuts, and seeds. On the contrary, the percentage of individuals who consumed meat, fish, and seafood groups decreased with an increase in the DDS tertiles. This finding might reflect that with an increase in the DDS, subjects decrease their meat intake and increase the intake of other healthy food groups such as fruits, vegetables, and dairy products. In addition, since the price of meat and fish is high in Iran, their consumption is low in many households. The results of a randomized clinical trial suggested that restricting meat, fish, and poultry intake improved some domains of short-term mood state in omnivores [31]. These results are consistent with the findings of another cross-sectional study which showed that vegetarians had better mood than omnivores [32]. Therefore, it can be deduced that with an increase in the DDS, the dietary pattern of the individuals could become more similar to the Mediterranean dietary pattern which is characterized by high intake of fruits, vegetables, whole grains, legumes, nuts, and seeds and low consumption of red meat [33]. The protective role of the Mediterranean dietary pattern against depression has been shown in some studies [34]. In addition, milk and dairy products, fruits and vegetables, eggs, legumes, nuts, and seeds have a high content of B vitamins, particularly vitamins B6, B12, and folic acid [35]. In the current study, a positive correlation was observed between the DDS and dietary intake of vitamins B6, B12, and folic acid. Several epidemiological studies have reported the protective effect of these vitamins against depression [36, 37]. For instance, based on a prospective study on American older adults, high intake of vitamins B6 and B12 is associated with lower incidence of depression after 12 years [36]. Moreover, one meta-analysis showed that after adjusting for confounders, low folate intake was significantly associated with the risk of depression [37]. Serotonin and dopamine deficiency are related to the etiology of depression. Vitamin B6-, B12-, and folate-derived coenzymes are involved in serotonin and dopamine synthesis and metabolism. Furthermore, vitamin B6 and B12 act as a cofactor for the conversion of homocysteine to methionine and cysteine, respectively. Insufficient dietary intake of these vitamins could lead to homocysteine accumulation and reduced synthesis of monoamines in the brain, which might play a crucial role in the etiology of depression [38]. We found a positive correlation between the DDS and the consumption of alpha-linolenic (ALA) and DHA. Based on the percentage distribution of food groups in DDS tertiles, a high DDS was associated with lower consumption of meat and fish, and higher intake of dark green leafy vegetables. So it is possible that the intake of fish, as the primary source of omega-3, is very low in women, as only 6.6% of them declared regular fish intake (data not shown). Therefore, the minor intake of dietary omega-3 fatty acids in our subjects could be attributed to the intake of vegetables. ALA is found in vegetables; this fatty acid can be converted to EPA and DHA in human body. However, fish consumption is considered the main source of EPA and DHA [38]. The results of one meta-analysis revealed that EPA and DHA levels were significantly lower in patients with depression, in comparison with healthy individuals [39]. In neurons, DHA is the primary component of plasma membrane phospholipids, and higher concentration of DHA improves serotonin receptor sensitivity in these cells via increasing the plasma membrane fluidity [40].

Regarding the role of oxidative stress in mental disorders, it has been shown that higher sensitivity of the human brain to oxidative stress could be due to high O₂ consumption, high intake of iron and polyunsaturated fatty acids, and low activity of antioxidant enzymes [41]. Food groups such as fruits and vegetables are rich in vitamins, carotenoids, polyphenols, and other bioactive compounds, so they provide a great amount of antioxidants [42, 43]. In addition, the riboflavin in milk and dairy products, and flavonoids, plant sterols, and tocopherols in nuts mark these foods as the natural sources of antioxidants [35]. In the current study, the DDS was positively correlated with the consumption of antioxidant nutrients, and increased DDS was associated with higher intake of food groups rich in antioxidants, such as vitamin A-rich fruits and vegetables, legumes, nuts, and seeds. Therefore, since several studies have indicated a positive correlation between a higher DDS and nutrient adequacy [15], increased DDS could be associated with increased consumption of nutrients and antioxidants, which in turn could have an important role in reducing the risk of depression. Furthermore, we previously showed that with an increase in the DDS increased the mean level of blood antioxidant markers, including total antioxidant capacity, superoxide dismutase, and glutathione peroxidase [44].

In the present study, women with mild, moderate, or severe depression had a lower DDS compared to healthy individuals; however, no significant relationship was observed between stress and DDS. Some studies have shown a relationship between perceived stress and unhealthy food consumption [45‐47]. Sedaqat et al. examined the association of snacking (fresh fruits, fruit juice, nuts and seeds, sweet beverage, salty snacks, sweet snacks, and fast food) with stress and depression in obese and non-obese women. They found that non-obese subjects in higher tertiles of natural fruit juice had higher ORs for stress, which might reflect higher energy intake with stress [45]. In another study, stress was associated with a lower intake of fruits, vegetables, protein, and higher consumption of salty snacks [46]. Oliver et al. reported a higher consumption of snack-type foods and lower intake of healthy foods such as fruits, vegetables, meat, and fish in stressful periods among university students [47]. Since the causal direction between nutrition and stress is not clear in most of the studies, further investigations are needed to determine the contribution of nutrition, particularly dietary diversity, to the incidence and development of stress.

This study has several limitations. First, the 24-h dietary recall is the main limitation for our study which has several limitations including difficulty in recalling consumed foods, their exact serving size, and under or over reporting [48]. In addition, using one 24-h recall period does not indicate an individual’s habitual diet. Second, no cause-and-effect relationship between DDS and stress and depression could be inferred in this cross-sectional study. There is even the possibility that food inadequacy or low dietary diversity could be the consequence of depression, and not its cause. Some studies have shown that depressed individuals seek to self-medicate with high-fat and high-sugar foods [49, 50]. Third, the sample size of this study is small which affects generalization of the results to the general population, since our subjects were 20- to 45-year-old women attending health centers. Despite these limitations, this is the first study to examine the relationship between DDS and stress and depression. The inclusion and exclusion criteria were well defined, and numerous potential confounding factors were controlled. In conclusion, we observed a significant inverse relationship between dietary diversity and severe, but not mild or moderate, depression in women. These results highlight the importance of a diet characterized by a greater variety and suggest important public health implications for depression prevention. Encouraging the consumption of various foods is important in nutritional interventions aimed at preventing depression. Future research exploring the effect of improved dietary diversity on mental health is warranted.