Effects of Meal Environment Cues on Appetite and Metabolic Responses and the Mediating Role of Mind-Body States

Background and Significance

Nutrition is a key determinant of healthy aging. Recent estimates suggest that, at a global level, poor diet is the second highest risk factor for early death after smoking, and contributes to one in five deaths [1]. Obesity, closely associated with poor diet and overeating, increases the risk of high-morbidity and -mortality conditions, including type 2 diabetes, cardiovascular disease, cancer and dementia [2, 3]. To reduce the risk of chronic disease in the population, several organizations have developed evidence-based dietary recommendations [4-6], which are used to guide health policies and programs. However, adherence to these recommendations remains a challenge [7], the so-called ‘nutrition-behavior gap’ [8]. Current recommendations place a strong emphasis on the composition of the diet, with specific guidance on quantification of macronutrient intake and dietary patterns (i.e. what to eat), and little or no mentioning of other aspects associated with the act of eating and its immediate context (i.e. how, why or when to eat). Nutritional epidemiology, the discipline behind dietary guidelines, is robust and relies on large datasets, but it is no short of limitations [9-11]. Complementary to this angle, several lines of evidence suggest that to be able to understand food-health relationships in their full extent, we need a more holistic view that integrates other important aspects, such as food quality versus quantity [12], the impact of meal timing –chrononutrition- [13, 14] and behavioral patterns [15, 16]. Anthropologists have also highlighted the limitations of ‘metrifying nutritional advice’, stating that the way humans eat is intimately linked to complex social and cultural associations that shape attitudes to food, eating behaviors, food choice, and ultimately nutrition and health [17, 18]. There is need for new perspectives beyond nutrition that can capture holistic aspects of food and eating, closely linked to the natural way humans relate to food.

The meal is the natural unit of eating in humans [19]. Beyond food composition, the context that surrounds a meal reflects cognitive, social, and emotional idiosyncrasies, and is also an important contributor to how and what a person eats. A body of research from the fields of consumer and sensory sciences has examined how the context in which food is presented and served during a meal can influence its perception, appetite, total intake and the overall experience [20-27]. However, these studies have focused primarily on consumption, acceptability or preferences, without leveraging these effects for the promotion of health, and without addressing in detail the mechanisms that could mediate those changes. Aside from the above studies, evidence in support of the importance of meals beyond nutrition in the study of food-health associations comes from cultural observation. Asian meal traditions, particularly in nations with good indices of healthy aging,

e.g. Japan and South Korea, are characterized by a rich set of norms around food and meals that guide people on how to eat as much as on what to eat [17, 28, 29], e.g. the shokuiku food and nutrition education curriculum taught in Japanese schools [30], or the intricate rules guiding Japanese [31] and Korean [32] food arrangements. These traditions emphasize the importance of naturality, seasonality, and a sense of aesthetic balance during meals [17, 28, 31]. Whether such focus on the meal context could have an impact on health healthy aging is currently unknown. Targeting aspects of the meal related to how to eat may represent a complementary strategy to facilitate healthy nutrition in the population.

Studying postprandial glycemic responses offers a window into the cardiometabolic impact of a meal. Postprandial hyperglycemia and glycemic variability can induce oxidative stress, inflammatory responses and other deleterious effects leading to endothelial dysfunction, representing an independent risk factor for adverse cardiovascular outcomes in both diabetic and nondiabetic populations [33-35]. Despite short- term clinical trials reporting mixed effects with low-glycemic index dietary interventions [36, 37], the value of postprandial glycemic responses has gained acceptance and it is current a major target in ongoing personalized nutrition interventions [38]. Physiologically, postprandial glycemic variability is affected by preprandial glycemic levels, meal composition, gastric emptying, insulin secretion, small intestinal glucose absorption, and hepatic and peripheral glucose metabolism [39]. There is growing evidence that factors that relate to the meal context can also play a role in postprandial glycemia, such as the order of food, the use of different utensils, or mind-body states (e.g. relaxation) [40-44]. Altogether, these findings support the use of postprandial glycemic responses as quick objective markers of the potential healthiness of a meal.

In this study, we will examine for the first time whether manipulations in the meal context can trigger mind-body states that impact appetite and the potential healthiness of a meal. Surprisingly, there has been very little research done or even awareness on this topic from the nutrition/science literature. It is possible that by de-emphasizing the primary reward aspects of food with a highly elaborated context and bringing a broader, deeper view on food (e.g. seasonality, the balance between foods, the aesthetic beauty of food and containers), satiation and satisfaction can be achieved after a meal with fewer calories, thus preventing overeating. Also, if the meal context triggers attributes and associations that induce a relaxation state, this could translate into beneficial metabolic effects of the meal. To answer these questions we have designed an experimental meal manipulation taking advantage of existing knowledge from cultural studies on Asian food culture. Experiments will be conducted using a new computerized tabletop environment developed in our laboratory and measuring effects on participants with sensitive physiological and cognitive parameters.

Specific Aims

Aim 1: To investigate whether a meal served in an Asian-inspired manner with references to nature, seasonality and aesthetics can impact appetite, specifically the satiating power of the meal, and post- meal glycemic responses. To address this aim, subjects will undergo two laboratory meals on two different days, in a randomized order, and counterbalanced across subjects. One of the meals will be representative of a plain, convenient, regular meal, served with a conventional arrangement. The other meal will be designed based on elements of Asian meals, particularly inspired by the art of Japanese food arrangement, under the supervision of Prof. Bestor. We will use elements that are universal and not culturally specific. Both meals will have the same food content but will differ in the arrangement and setting. Throughout the duration of the study subjects will wear a noninvasive continuous glucose monitoring (CGM) system. We expect that the meal served in an Asian-inspired manner will have higher satiating power (defined as change in appetite rating per kcal), higher overall satisfaction and a better glycemic response profile, characterized by a slower elevation in glucose levels, lower glycemic peak and smaller area under the curve.

Aim 2: To examine whether the effects of an Asian-inspired meal on satiating power and glycemic response are mediated by changes in physiological markers indicative of autonomic responses related to relaxation (heart rate variability, respiratory rate, electrodermal activity) and cognition (fixation patterns via eye-tracking). During the abovementioned two meals subjects will also wear physiological sensors (EKG, chest belt, a wristband and eye-tracking glasses). Based on the results of Aim 1 and physiological changes detected by these sensors, we will examine the potential mediation role of relaxation and autonomic changes induced by the presence of cues at the meal. We hypothesize that the Asian-inspired meal will be associated with a relative increase in vagal tone, defined as decreased respiratory rate, increased heart rate variability and reduced electrodermal activity. This will be associated with a more focused fixation pattern during the meal, measured with eye-tracking.