Metabolic syndrome refers to the combination of central obesity with any two of the following four factors: raised triglycerides, reduced high-density lipoprotein (HDL) cholesterol, raised blood pressure (BP) and raised fasting glucose (1). Metabolic syndrome is associated with an increased risk of all-cause mortality (relative risk [RR], 1.23) and cardiovascular disease mortality (RR, 1.24) (2). Several studies have found that people with metabolic syndrome have a higher risk of cognitive impairment and dementia than do those without metabolic syndrome. The association between metabolic syndrome and cognitive health is complex and multifactorial, being influenced by factors including age, genetic factors, education, lifestyle, pro-inflammatory process and oxidative stress. These factors contribute to deficits in memory, visuospatial and executive abilities, speed processing and general cognitive ability and lead to cognitive decline. Lifestyle modifications, such as a healthy diet, regular exercise and weight loss, may alleviate metabolic syndrome and reduce the risk of cognitive decline. Therefore, it is essential to manage metabolic syndrome to promote cognitive health and prevent cognitive decline (3, 4, 5).
The Mediterranean–DASH Intervention for Neurodegenerative Delay (MIND) diet is a combination of the DASH diet and the Mediterranean diet. The MIND diet (6, 7) emphasises 10 brain-health-promoting food groups, namely green leafy vegetables, other vegetables, berries, nuts, beans, whole grains, seafood, poultry, olive oil and wine, and limits five unhealthy food groups (red meats, butter and stick margarine, cheese, pastries and sweets and fried/fast food). Evidence from epidemiological studies has demonstrated that adherence to the MIND dietary pattern is associated with improved cognitive performance and a reduced risk of cognitive decline in older adults (8, 9, 10). A 12-year longitudinal cohort study found that the MIND diet has an ameliorative effect on cognitive impairment (11). A systematic review of 13 studies also showed that adherence to the MIND diet was associated with improved cognitive function, especially in older adults (12), while several other studies have reported it to be associated with improved verbal memory and global cognitive performance, as well as a slower rate of cognitive decline after stroke and a lower risk of dementia (6, 7, 13, 14). A recent cross-sectional study and randomised controlled trial (RCT) found that the MIND diet is inversely associated with the odds of reduced HDL-cholesterol and general obesity (15, 16). The MIND diet emphasises the consumption of fatty fish, and long-chain n-3 fatty acids found in fish may reduce amyloid-beta (Aβ) formation and oxidative damage. These fatty acids also promote lipid metabolism, thereby inhibiting fat synthesis and improving insulin sensitivity, with the underlying mechanism involving increased expression of peroxisomal acyl-CoA oxidase that can increase energy expenditure in the form of heat and reduce energy storage in the form of fat (17, 18).
Two signature foods of the MIND diet are berries and green leafy vegetables. They are rich in flavonoids, folate, vitamin E and carotenoids, and these compounds have been shown to have antioxidant and anti-inflammatory effects that inhibit Aβ formation (19, 20). These mechanisms directly impact brain health and may also indirectly impact it through the cardioprotective effects of certain nutrients.
Forest bathing (FB) is a traditional Japanese practice of mindful immersion into nature by connecting through all five senses. Using a set of experiential thresholds for sensory activity, an FB coach guides the participants to immerse themselves deeply into nature and build a connection with the forest (21). FB has been found to directly decrease sympathetic nervous system activity, cortisol levels, and salivary amylase activity and lead to a relaxed state (21, 22). Recent studies have found that FB significantly reduced systolic BP by 5.4–24.6% and diastolic BP by 7–29.5% in individuals with high initial BP (21, 22). FB also has restorative effects on cognitive function, thus improving cognitive abilities (23, 24). For example, participants have been reported to experience directed attention improvement, improved memory and enhanced creativity after exposure to forests (25, 26, 27). Thus, this approach could be suitable to enhance cognitive function and relaxation in middle-aged and older individuals.
Studies have evaluated the cognitive ability-enhancing effects of the MIND diet in general and obese Western populations. Our previous pilot study tested the cardiovascular health outcomes and participants’ acceptance of a combined MIND + FB intervention (28). In the current study, we tested the hypothesis that the MIND diet is effective in maintaining/enhancing cognitive function and metabolic health outcomes in people of Chinese ethnicity and that FB enhances the effects of the MIND diet. To the best of our knowledge, no study has investigated the effects of a combined MIND + FB intervention in enhancing cognitive functions and metabolic health outcomes in people of Chinese or any other ethnicity. The objectives of this study were to examine 1) the preliminary effects of the MIND + FB intervention on the cognitive function and metabolic health of community-dwelling older adults and 2) adherence to the interventions in this population.