Background: Depression and anxiety has increased over the past decades in Chinese adolescents. The relationship between dietary behaviors and mental illness remains unclear.
Objective: This study examined how dietary patterns were associated with sleep quality, physical activity, and symptoms of mental illness.
Methods: A total of 169 Chinese adolescent students aged 11-19 years were included in this cross-sectional study. Weekday and weekend dietary behaviors were measured separately. Physical activity, sleep quality, and anxiety and depression symptoms were assessed. We computed and compared the correlations between the measures in boys and girls alone and middle and high schoolers alone. We also compared weekdays vs. weekends for these relationships.
Results: As compared to boys, girls performed fewer physical activities and showed more symptoms of depression and separation anxiety. Middle vs. high schoolers demonstrated more physical activities, better sleep quality, and fewer symptoms of depression, panic disorder, and separation anxiety. There were significant inverse relationships between dietary quality and sleep quality. Unhealthy dietary intake was associated with less anaerobic activity and higher levels of general anxiety. In addition, from Table 1., the girls’ dietary pattern was found to be negatively associated with general anxiety, which was not found in boys. However, boys’ dietary quality increases as their aerobic exercise frequency increases. In Table 2., while both middle and high schoolers’ sleeping quality was positively associated with nutrition intake quality, high schoolers exhibited symptoms of separation anxiety and general anxiety as they consumed a low-quality diet. In Table 3., weekdays/at-school dietary quality was significantly associated with sleep quality and duration, and general anxiety. Weekend dietary intake quality was associated with anaerobic exercise. All the associations are shown in scatter dot plots in Figure 1.
Conclusion: Dietary behaviors were associated with physical activity, sleep quality, and mental problems. The associations showed differences between sexes and between grades. Healthy nutritional intake, adequate sleep duration, and frequent exercise may help prevent the development of mental illness.
Table 1. Descriptive statistics of demographics and clinical measures in boys and girls separately
Table 2. Descriptive statistics of demographics and clinical measures in middle schoolers and high schoolers separately
Table 3. Comparison between weekday and weekend diet behaviors.
Figure 1. Scatter plots of significant correlations. (A) Weekday diet and sleep duration; (B) Weekday diet and sleep problems; (C) Weekday diet and general anxiety; and (D) Weekend diet and anaerobic activity.
Discussion:
4.1 Current Diet in China
China has switched from the traditional plant-based diet to a Westernized diet, rich in animal-based and processed foods, consistent with our findings. Specifically, only half of the students meet the recommended for whole grain, legume, or nuts intake; around 51% of students consume animal products daily; 88% of the students snacked on sweet and processed food every day. Institutional setting is shown to be involved in the increasing prevalence of unhealthy dietary consumption in children. Eating at the school canteen during weekdays, students consume fewer vegetables, fruits, and whole grains than eating at home or off-campus during the weekend (75% vs. 91%, 77% vs. 88%, and 52% vs. 56%, respectively). This should not be surprising, however, since research illustrated two decades ago that eating with family was associated with increased fruits and vegetables, less processed food, less high-fat, and more fiber and micronutrient food (Gillman et al., 2000).
Another factor may be the interpersonal relationship with family or caretakers. One theory of worsened Chinese childhood dietary quality is related to grandparental care. In China, most parents are preoccupied with work burdens; children are taken care of by grandparents. In 2011, the rate of children under grandparental care increased from 40% to 56% since 1991 (Zhao, 2017). A study elucidated the influence of grandparental care on childhood obesity, showing that grandparental care increases children's obesity rate by 3.6 percentage points (Liu, Zhao, & Zhong, 2022). The culprit is insufficient education of caretakers regarding nutrition. In addition, the past famine experience of grandparents induces a fear of hunger, which translates to indulgence, overfeeding, and overprotection from physical chores, ultimately aggravating unhealthy dietary patterns and childhood obesity (Liu et al., 2022).
4.2 Potential Biological Mechanism
An unhealthy diet consisting of pro-inflammatory foods exacerbates systemic inflammation and increases the risk of depression (Irwin & Miller, 2007). The hypothalamic-pituitary-adrenal (HPA) axis plays a key role in depression, and a hyperactive HPA can lead to cognitive dysfunction and low mood (Mikulska, Juszczyk, Gawrońska-Grzywacz, & Herbet, 2021). Unhealthy diets are usually characterized by high glycemic-index foods, which lead to elevated cortisol and trigger a vicious cycle of chronic stress and unhealthy dietary behaviors (Sominsky & Spencer, 2014). Recent research has also shed light on the role of the gut microbiome in mood regulation (Firth, Gangwisch, Borsini, Wootton, & Mayer, 2020): The gut-brain axis allows the gut microbiome to influence emotion; processed food and animal-based food, which induce inflammation, is associated with mood disorders and is detrimental to various brain functions, including cognitive decline, and hippocampal dysfunction. Gut microbiota may also play a positive role in neurotransmitter metabolism such as serotonin synthesis (O’Mahony, Clarke, Borre, Dinan, & Cryan, 2015). Therefore, a higher intake of animal foods (fats and cholesterol), refined carbohydrates, and lower consumption of dietary fiber (fruits, vegetables, legumes, and whole grains) are associated with shorter sleep duration (Theorell-Haglöw et al., 2020). Therefore, eating a variety of fiber-rich food, polyphenols, and unsaturated fatty acids should be advocated for students to alleviate the stress engendered by the intense academic environment. Meanwhile, schools should take heed when planning the canteen menu to decrease the usage of ingredients high in saturated fats, refined carbs, and artificial sweeteners.
