The prevalence of obesity has remarkably increased over the past decades, making obesity the most critical public health issue. Although the etiology of this condition is complicated, maladaptive eating behavior is acknowledged to be the major contributor1. Thus, eating behaviors are significant considerations of the public health burden2. There is growing interest in research on eating behaviors due to their importance in obesity. Previous studies have examined three different dimensions of eating behaviors: food intake, proportion, and diversity3–5. Food intake refers to the amount of food consumed. This is the most remarkable eating behavior phenotype, since an energy imbalance, the main feature of overweight condition and obesity, occurs when the intake exceeds the expenditure5. Food proportion refers to the percentage of food group sections composing the total food intake6. There are controversial results regarding the relationship between food proportion and bodyweight, showing all three possible outcomes (positive, negative, and no significant associations)1,2,5. Food diversity is related to the distribution or diversity of dietary patterns among different food groups4. Although few studies have investigated the role of food diversity in health outcomes, there is an increasing recognition that food diversity can be particularly relevant to obesity and blood glucose control in diabetes3,6. Moreover, it may be a principal indicator for evaluating the nutritional status of the diet as a whole. A comprehensive understanding of eating behavior requires the consideration of multifaceted factors. Therefore, understanding the mechanisms for controlling human eating behaviors and developing the ability to assess them is critical in establishing effective obesity treatments.
From a psychological perspective, there are three fundamental questions related to studying human eating behaviors: How much do we eat (food intake)? How much do we choose to eat from specific food groups (food proportion)? How diverse are the categories of the food we eat (food diversity)? There is no doubt that emotions and eating behaviors interact with each other. For instance, emotion could influence food intake and choice by altering appetite or food availability, while emotional transitions can also result from food intake and choice7. In addition, people regulate eating behaviors according to contextual aspects such as social settings5, food variety8, food palatability9, memory of recent eating10, and motives for eating regulation11. The great majority of research on eating behaviors within psychology is about managing food intake, choice, and variety, since these can be associated with obesity and eating disorders.
One of the important factors in eating behaviors is insulin resistance (IR), a dysmetabolic status in which the peptide hormone insulin shows reduced biological effect on peripheral target tissues. Previous studies have revealed that IR is closely related to obesity, metabolic diseases such as type 2 diabetes (T2D) mellitus and cardiovascular disease, and cognitive impairment. IR is associated with the central nervous system delivering information regarding energy homeostasis and is positively associated with adiposity12,13. A previous study also reported that IR patterns correlated positively with eating behaviors such as overeating and food craving, potentially stimulating altered regulation of the homeostatic system14. Accordingly, reducing the food calorie intake decreases both body weight and IR15,16. In further human brain studies, insulin activation selectively impaired the prefrontal cortex and hypothalamus of overweight and obese people14,17. However, the role of IR during changes in eating behavior, food intake, proportion, and diversity for weight loss has not been comprehensively investigated.
To comprehend human eating behaviors, it is critical to establish assessment methods for analyzing food intake, proportion, and diversity18. Since the nature of eating behavior is complicated, an optimal protocol for its assessment has not yet been defined. In fact, current protocols to analyze eating behavior lack precision and have systematic limitations. Some past studies insisted upon approaches that consider both internal validity (reproducibility) and external validity (resemblance to real-world eating behavior)19. Thus, a comprehensive assessment indicating ideal circumstances (high internal validity) and real-world conditions (high external validity) will promote the efficacy and safety of new medical interventions for obesity using randomized controlled trials (RCTs)20.
Among the protocols focused on internal validity (reproducibility), many techniques and methodologies have been developed based on experimental conditions of food intake, proportion, and diversity. The most common method involves allowing participants to take meals with no restrictions on the amount of food19. This method has shown good validation for total energy intake between two equal sessions, presenting good reproducibility21,22. The internal validity of buffet test-meals in laboratory research is generally high because they provide the maximum sensitivity level and allow for manipulation of the intervention and the outcomes19. It is also practical to categorize food into either healthy or unhealthy groups based on a structured procedure. However, under these conditions, there is a high risk of excluding the cognitive and physiological aspects of eating behavior.
Besides the buffet test-meal, several studies have highlighted the importance of considering the real-world eating context, focusing on external validity (resemblance to real-world eating behavior)23,24. Most recent research has emphasized using digital technologies such as mobile apps to aid dietary assessment25. Food diaries using mobile apps enable the use of advanced technological features, such as wireless communications and portable designs, allowing people to reflect real-life eating behavior and situations in dietary research. Thus, these apps are suitable for determining eating behavior at breakfast, lunch, dinner, and snacks, representing daily patterns. While the external validity of mobile apps for assessing eating behaviors is high, several methodological limitations threaten internal validity19. The most severe problem is that the chance of data collection errors is relatively high, usually due to misreporting of energy intake. However, little research has examined the validity of logging food intake and choice through mobile apps.
This study explores the role of psychological characteristics and IR in eating behaviors by implementing a buffet test-meal (experimental setting) and a food diary using a mobile application (real-world setting) to develop precision medicine in obesity clinics. The predictors and mechanisms related to eating behavior changes based on lifestyle modification clinical trial data (shown in Fig. 1) were investigated.