In the present study, we have shown that a high adherence to a DASH dietary pattern, characterized by high consumption of fruits and vegetable, as well as low intake of red and processed meat, sugar-containing beverages and sweets, is associated with lower odds of stress and sleep disturbance in young women.
Although the relationship between dietary patterns and mental health is unclear, it is possible that psychological stress and eating habits are related. Cartwright et al. showed that children who eat fatty foods and snacks frequently, and consume low amounts of fruits and vegetables, had greater levels of stress . Excessive stress can affect the QoL and a previous study reported an inverse association between stress score and QoL among university students, those who face an increased risk of mental conditions due to different stressors .
Improvements in diet and lifestyle may have beneficial impacts on depression symptoms. We found that depression score was negatively associated with vegetables intake and this is in line with the findings of previous studies [29, 30]. A meta-analysis of eighteen studies with 446,551 participants has indicated that fruit and vegetable consumption is inversely associated with the risk of depression . Additionally, a prospective cohort study reported that frequent use of vegetables can play a protective role against depression in the elderly .
The mechanisms by which vegetables, or ‘healthy dietary patterns, decrease the risk of depression is not completely clear , but some nutrients including B group vitamins, n-3 fatty acids and antioxidant have been thought to be related with depressive behavior . Oxidative stress and inflammation can both increase depressive symptoms by their effects on neurons of the autonomic nervous systems. Folate and B group vitamins, with their beneficial effects on inflammation and oxidative stress, are necessary for neuronal function and their deficiency is associated with depression, anxiety and dementia . Non-nutrient phytochemicals with antioxidant activities found in vegetables could be another probable mechanism for this improvement .
Nuts are a part of the human diet and are considered to be health-promoting nutrients. Our result showed that the consumption of nuts, legumes and seeds is associated with a higher QoL. These nutrient-rich foods contain substantial amounts of polyphenol antioxidants, macro- and micro-nutrients and other beneficial bioactive compounds which it’s intake decrease oxidative stress and inflammation, so can prevent several human disorders and increase the QoL .
We found an inverse relationship between sodium intake and QoL. Previous studies reported that excessive salt intake not only can lead to hypertension, but also plays an important role in endothelial dysfunction and cardiovascular and kidney disease progress as well as reduce life expectancy [34, 35]. Therefore, a diet containing low amounts of salt may be considered a potential strategy to control hypertension, decreases cardiovascular morbidity and improve the QoL.
We found a positive relationship between dietary whole grain intake and sleep duration which is consistent with the study of Grandner et al, who showed that short sleepers report higher intakes of protein and carbohydrate, but low dietary fiber consumption; altered sleep duration is probably associated with changes in the secretion of appetite-related hormones .
Diet plays an important role in cognitive function, especially in childhood and the growth period, due to providing the components for nerve formation and brain development . In the current study, we have found an inverse relationship between cognitive abilities score and red/processed meat consumption. Consistently, it has been show that Western dietary pattern, characterized by high intake of processed foods, sweet and red meat, has been found to be associated with greater levels of mental distress in adolescents . Additionally, a cross-sectional study conducted on the adult population in UK demonstrated that higher consumption of red meat is related to weaker cognitive functions such as reasoning ability and short-term memory .
Due to the importance of sleep on QoL and its impact on psychological wellbeing, it is essential to identify the main factors that may effect this cycle. Eating habits modification is a potential approach to prevent sleep complications. Rostami and co-researchers demonstrated that greater commitment to a DASH diet is associated with lower prevalence of insomnia . Results of the present study indicated that sweetened beverage intake was associated with grater odds of insomnia. Caffeine, as an important active component of sweetened beverages, has been showed to be inversely associated with sleep duration and may disturb sleep, leading to difficulty falling asleep, insomnia, day time sleeplessness .
Indeed, one of the most significant findings of the current study was that adherence to a DASH-type diet decreased the likelihood of difficulty in initiating sleep. High intake of sweets can increase the glycemic response and induce oxidative stress. Long-term sugar intake has been showed to negatively affect brain serotonin 5-hydroxytryptophan receptor sensitivity in laboratory animal models [42, 43]. In another study, adherence to higher fat/lower carbohydrate diet was associated with a reduction in serotonin release in the hypothalamus of Wistar rats . There is a high likelihood that the consumption of vitamins, minerals and fibers may improve sleep quality. Tryptophan is an essential precursor to serotonin syntheses, a neurotransmitter known for controlling the sleep cycle and inducing feeling of sleepiness. Group B vitamins are also required for serotonin synthesis. Therefore, a balanced and diverse diet that can provide fruits, vegetables and whole grains, like DASH, can improve sleep .
We showed that individuals with a greater adherence to a DASH-style diet had a higher intake of potassium, magnesium, and fiber. Because of the content of green leafy vegetables, nuts, seeds, legumes and whole grains, the DASH has a high amount of magnesium. Also, fruits and vegetables in the DASH diet provide a high content of potassium and fiber. Dietary fiber has low energy because it is resistant to breakdown by gastrointestinal enzymes, and fiber-containing foods i.e. whole grains, vegetables and fruit have a low energy density . On the other hand, as is consistent with our results, Davison et al. reported that higher levels of energy (Kcal), fiber, B vitamins, calcium, phosphorus, potassium, and magnesium intakes were associated with better mental health .
To the best of our knowledge, this is the first study examining the correlation between adherence to DASH diet and neuropsychological functions in young women. But, the present study has a number of limitations. First, we used a cross-sectional design that cannot demonstrate causality. Difficult sleep initiating was evaluated using self-reported questionnaires which may be predisposed to bias. Moreover, a FFQ is an unreliable tool for assessing the sodium intake. Finally, we did not evaluate physical activity in our population.