The Effectiveness of MIND Diet and Forest Bathing on Stress Reduction

This project is a pilot study to examine the effectiveness of Mediterranean DASH Intervention for Neurodegenerative Delay (MIND) Diet and Forest Bathing (FB) on reducing psychological stress. In recent years, mental health has become an increasingly important issue in Hong Kong. More people in Hong Kong are seeking help for mental health issues such as anxiety, depression, and stress. A 2020-2022 survey found that 1.2% of individuals aged 15 or above reported depression and 0.9% reported anxiety. Females had higher prevalence rates than males, and individuals aged 55-64 had the highest rates of depression (1.7%) and anxiety (15%). Conventional treatments have not been sufficient in managing or addressing chronic stress in individuals. Several factors including dietary intake and forest visits have been reported to be associated with psychological health. Research suggested that the MIND diets anti-inflammatory and pro-inflammatory components may reduce anxiety and depression, and forest bathing (FB) can reduce physiological and psychological stress by decreasing sympathetic nervous system activity and having a restorative effect. However, it is unclear if these approaches are effective for older adults with mild to moderate levels of psychological stress, particularly in the Chinese population. Additionally, there is a gap in the literature regarding the relationship between the MIND diet and psychological stress among the Chinese population. Therefore, it is important to investigate the potential impact of the MIND diet and forest bathing on psychological stress among older Chinese individuals.

The objectives of this study will be to:

1. examine and compare the therapeutic effects of the MIND-FB, FB and routine care on psychological stress (emotional states) and physiological stress (blood pressure and salivary cortisol level) at 4 weeks.
2. examine and compare the sustained effects of the MIND-FB, FB and routine care on these psychological and physiological stress at 12 weeks.
3. examine the therapeutic effect of the MIND-FB, FB and routine care by controlling for other individual characteristics (demographic and lifestyle characteristics, health history and current medication use).

In the short term, the study will benefit participants by providing them with either the MIND diet and forest bathing intervention or routine care, which is expected to reduce the level of psychological stress. The study results will be published in international peer-reviewed journals and presented at conferences. In the medium term, the project will offer evidence for local healthcare providers on the use of similar therapies for adults with psychological stress.

Introduction

Psychological Stress has been defined as a state of mental strain, distress, or anxiety, resulting from various challenging circumstances or events. In recent years, the coronavirus disease 2019 (COVID-19) pandemic has significantly impacted mental health worldwide, with notable increases in the prevalence of anxiety and depression, according to a scientific brief published by the World Health Organization. The brief also indicated that young people, women, and individuals with chronic diseases were at higher risk of experiencing heightened levels of stress, anxiety, and depression. In Hong Kong, in addition to the impact of the pandemic, individuals face high levels of stress and pressure in daily living, such as high cost of living, competitive work environment, and family relationships, which can result in burnout among individuals.

The benefits of the MIND diet in promoting mental health

The Mediterranean - Dietary Approaches to Stop Hypertension (DASH) Intervention for Neurodegenerative Delay (MIND) diet combines the Mediterranean and DASH diets and focuses on ten brain-healthy foods while restricting five detrimental food groups. A review study suggested that the diet might positively impact older adults' mental health due to the anti-inflammatory and pro-inflammatory properties of its components. Specific nutrients, such as long-chain n-3 fatty acids in fish and flavonoids in berries and green leafy vegetables, exhibited antioxidant and anti-inflammatory properties that inhibited amyloid-beta (Aβ) formation, which could cause brain atrophy. Limiting the intake of certain foods, such as butter, margarine, pastries, sweets, saturated fats, and trans-fats, could enhance blood-brain barrier function and mitigate Aβ aggregation. These mechanisms may have a direct impact on brain health and indirectly affect psychological health.

Several recent studies have examined the relationship between adherence to the MIND diet and mental health outcomes. One case-control study found that high adherence to the MIND diet was associated with lower anxiety scores (OR = 0.03) and significantly reduced severity of anxiety disorders (β=-3.63, p<0.001). Another cross-sectional study found that the MIND diet was significantly associated with lower odds of depression (OR=0.62) and anxiety (OR=0.61), but not psychological stress (OR=0.57). However, a cohort study did not find a significant association between MIND diet adherence and incident depression but did find reduced depression risk with the consumption of fruits, and nuts, and avoidance of fast or fried foods. Additionally, another cohort study found that the highest adherence group to the MIND diet had lower rates of depressive symptoms over time compared to the low adherence group.

The effectiveness of FB in promoting mental health

In recent years, the Japanese, Korean, and Taiwanese governments have promoted forest bathing as a therapeutic practice for urban residents. This practice involves intentional exposure to forested areas within the city to promote relaxation and well-being. Forest bathing, also known as Shinrinyoku in Japan, is a sensory experience that entails immersing oneself in natural surroundings and mindfully engaging all five senses. Theories, such as Kaplan and Kaplan's Attention Restoration Theory (ART) and Ulrich's Psycho-evolutionary Stress Reduction Theory (PET), suggested that exposure to natural environments could promote positive mood, reduce stress, restore cognitive resources, and improve mental functioning. Empirical studies have found that forest bathing has a direct effect on decreasing sympathetic nervous system activity and stress hormone levels, leading to a relaxed state. Scientific literature reviews have suggested the therapeutic effect of forest bathing on stress-related disorders, including depression, anxiety, attention deficit and hyperactivity disorders (ADHD), and stress. Therefore, forest bathing is considered a useful practice for reducing symptoms of stress and promoting relaxation and well-being.

The research team conducted a pilot randomized controlled trial (RCT) to test the therapeutic effect in three groups (the MIND diet plus FB (MIND-FB) group, the MIND group, and the control group) of older Chinese adults with hypertension. The MIND-FB group showed significant decreases in the score of state (-5.28) and trait anxiety level (-4.28), total emotional state (-6.28), tension-anxiety (-2.2), fatigue (-1.4), anger (-1.24) and confusion (-1.28) after the 4 weeks of intervention. However, it is unclear if these approaches are effective for older adults with mild to moderate levels of psychological stress, particularly in the Chinese population in reducing psychological and physiological stress. Additionally, there is a gap in the literature regarding the relationship between the MIND diet and psychological stress among the Chinese population. Further study is needed to investigate the potential impact of the MIND diet and forest bathing on psychological stress among older Chinese individuals. This randomized controlled trial will target older individuals between the ages of 50 and 75 who are at higher risk of mental illness and will investigate the effectiveness of the MIND diet and forest bathing in reducing psychological and physiological stress. We hypothesise that both interventions will offer significant mental health benefits to older Chinese individuals, with a greater reduction in psychological stress compared to physiological stress.