factors), that helps coordinate efforts that connect policies, systems, and environmental interventions.
2.6 How We Feed: Nutrition and Nutrition‐related Health Disparities
Nutrition‐related disparities are well documented, with low nutritional value foods and low‐quality diets more prevalent among disadvantaged than nondisadvantaged populations [54]. This could be related to food deserts and food insecurity, which are more likely to be concentrated in neighborhoods with a high proportion of minority and low‐income populations. According to the United States Department of Agriculture (USDA), food deserts include census tracts that are low‐income (i.e., where a portion of residents make below a threshold income) and low access (i.e., where a significant portion of the residents is far from a supermarket). The USDA defines food insecurity as “the limited or uncertain availability of nutritionally adequate and safe foods or limited or uncertain ability to acquire acceptable foods in socially acceptable ways” [55].
Residents of minority and low‐income neighborhoods have limited availability of affordable and healthy foods, and must rely on the nonhealthy/non‐nutritious foods available in their proximity or incur significant tangible (e.g., monetary) or intangible (e.g., long distance travel) costs to buy more expensive healthy options [56]. Low‐income neighborhoods have lower availability of fruits and vegetables and nutrient‐dense foods [56]. Such neighborhoods also include more small stores than large supermarkets. This is important because prices of staple food items such as milk, eggs, fruits, and vegetables are higher in small stores compared to large ones, with one study finding the difference ranging from 10% to 50% higher [56]. Smaller stores also have fewer fresh items and sell smaller units of packaged items than supermarkets, resulting in higher prices [56, 57]. One study estimated that a resident of a poor Black neighborhood lived 1.1 miles farther from the closest supermarket than a resident of a poor White neighborhood [57]. Further, low‐income neighborhoods have a high concentration of unhealthy food restaurants (e.g., fast food), thus adding to the limited availability of healthy food options [57]. As a result, and in contrast to the diet of higher‐income populations, the diet of low‐income populations generally costs less than a healthier, nutrient‐dense diet because it is of low nutritional value and low quality [54].
Disparities in intake of nutritious food are associated with disparities in health and well‐being. Populations whose diet is mostly of low nutritional quality experience poor dietary patterns, including low fruit and vegetable intake. They also experience lower levels of serum carotenoids and higher rates of obesity and high blood pressure, which are associated with diabetes, cardiovascular disease, and other chronic diseases [54, 56, 57]. Even after controlling for home food‐environment factors, an association persisted between neighborhood food‐environment factors such as food deserts and obesity [58].
Healthy, nutrient‐dense food is often neither available nor affordable in communities where health disparity populations live. Consequently, those populations experience a high prevalence of nutrition‐related diseases and conditions. Possible biological pathways linking nutritional stressors to health disparities include allostatic load and changes to the microbiome. Both pathways are responses to local inflammations caused by nutritional stressors, including inadequate intake of key nutrients or a high intake of calorie‐dense foods, such as frequent fast food meals. The hypothalamus, which plays a central role in regulating feeding and nutrition, is subject to modulation by local inflammatory events. Studies have shown that normal physiological control of feeding by the hypothalamus can be disrupted by local inflammation, some of which is influenced by high levels of dietary LCFA [4, 11]. This local inflammation blunts the response of the hypothalamus to leptin and insulin, thus implicating a role for inflammation in the evolution of obesity.
Alteration of the microbiome can also result from nutritional stressors. The microbiome, mostly located in the gut, is made of microorganisms that are largely beneficial but can sometimes be harmful. Both types exist in harmony in healthy bodies, but the balance can be disrupted by factors such as infectious disease (and frequent use of antibiotics), chronic stress, or malnutrition. Health disparity populations often experience one or more of these factors, thus resulting in frequent detrimental alterations to their microbiome, thus increasing their susceptibility to disease.
Nutrition‐related disparities contribute to disparities in the prevalence, incidence, and burden of disease through their impact on allostatic load and the human microbiome. Efforts to decrease those disparities and their effect entail modifying the environments that promote inadequate nutrition and improving understanding of the mechanisms through which inadequate nutrition contributes to health disparities. In terms of environmental changes, moving populations to better environments, although possible (e.g., Moving to Opportunity program [59]), is not scalable or sustainable. Interventions have been tested to improve the physical and social environments to support healthier food choices. This evidence needs to be effectively disseminated and scaled up. Future research needs to examine the feasibility, scalability, and sustainability of interventions to improve the physical and social environments that promote and sustain healthy nutrition among health disparity populations. With regard to mechanisms, more research is needed to understand how nutritional stressors contribute to allostatic load and affect the microbiome, and the extent to which changes in the microbiome can contribute to health disparities. In particular, linking environmental, social, and behavioral nutrition‐related data to data on the microbiome would enable examining how these contextual factors affect the microbiome in various racial/ethnic groups [60].
2.7 How We Feel: Mood and Depression
Depression is ranked by the World Health Organization (WHO) as the leading cause of disability around the world [61]. It is also the major contributor to deaths by suicide, approximately 800,000 per year [61]. Worldwide, depression prevalence was 4.4% in 2015 (about 322 million people) with higher prevalence among females (5.1%) compared to males (3.6%) [61]. In 2015 in the United States, 6.7% of adults had experienced at least one major depressive episode (MDE) in the previous year and 4.3% had experienced an MDE with severe impairment. This national survey defined MDE using the standard criteria from the Diagnostic and Statistical Manual of Mental Disorders–4th edition (DSM‐IV) as “adults who had a period of 2 weeks or longer in the past 12 months when they experienced a depressed mood or loss of interest or pleasure in daily activities, and they had at least some additional symptoms, such as problems with sleep, eating, energy, concentration, and self‐worth.” Such adults were considered to have experienced an MDE, while those whose depression caused “severe problems with their ability to manage at home, manage well at work, have relationships with others, or have a social life” were considered to have an MDE with severe impairment [62].
Major depressive disorder 1 (MDD) inflicts serious economic and social costs on society [63]. In addition, it has been associated with low educational attainment, marital disruption, unstable employment, and increased risk of teenage pregnancy among those who experience early onset [64]. Moreover, it has been associated with significant decreases in role functioning, including low marital quality, low job performance, and low income. MDD has also been implicated in increased risk of onset, persistence, and severity of many chronic physical disorders, as well as increased early mortality due to suicide and a variety of physical disorders [65].
Emotional stress, whether acute or chronic, is an established causal factor in the onset and progression of depression [66]. Stress arises when individuals experience demands (physical or psychological) or threats for which they do not have sufficient social and material resources to respond to and thereby ameliorate the resulting health effects [67]. In contrast, when sufficient resources are available to individuals, these demands or threats are perceived as challenges that promote growth and resilience [68]. Stress hormones, such as cortisol and adrenaline, released in response to stressors are usually adaptive and beneficial in the process of allostasis, or maintaining stability during times of change [69]. However, when these stress hormones are not turned off when not needed, are overused, or are not turned on when needed, allostatic load ensues, a wear and tear on the body and the brain that is evident in major depressive illness