On July 9-10, 2014, the Institute of Medicine’s Food Forum hosted a public workshop to explore emerging and rapidly developing research on relationships among the brain, the digestive system, and eating behavior. Figure 1-1 illustrates these complex relationships, as well as the influence of biology and the environment, as described by the speakers throughout the workshop.
Drawing on expertise from the fields of nutrition and food science, animal and human physiology and behavior, and psychology and psychiatry as well as related fields, the purposes of the workshop were to (1) review current knowledge on the relationship between the brain and eating behavior, explore the interaction between the brain and the digestive system, and consider what is known about the brain’s role in eating patterns and consumer choice; (2) evaluate current methods used to determine the impact of food on brain activity and eating behavior; and (3) identify gaps in knowledge and articulate a theoretical framework for future research.
The organization of this workshop summary parallels the organization of the workshop presentations and panel discussions. The workshop was divided into four sessions, with a panel discussion at the end of each
______________
1 This workshop summary is a factual account of the presentations and discussions that occurred during the workshop. All of the information provided here was presented either verbally or visually (on slides) during the workshop. The goal of the workshop was not to reach consensus on any issue or to formulate recommendations. The opinions and suggestions summarized here were those of individual speakers or audience members and should not be construed as reflecting consensus on the part of the Institute of Medicine, the Food Forum, the workshop planning committee, or any other group.
FIGURE 1-1 Relationships among the brain, the digestive system, and eating behavior.
NOTE: Environmental cues include commercial, physical, social, and cultural influences.
session (see the workshop agenda in Appendix B). The panel discussions served to clarify issues, provide additional perspectives, and identify gaps in knowledge.
The workshop began with an exploration of how the presence of food in the gut triggers signals to the brain about nutrient content, character, and volume and how that information, in turn, impacts further food intake. Timothy Moran of Johns Hopkins University explained how most information received by the brain about gastrointestinal contents is derived from vagal afferent feedback signals,2 some of which come from the stomach and others from the intestine.
While vagal signals from the stomach are different from those arising in the intestine, the two intersect in the hindbrain, where together they play
______________
2 Vagal afferent signals are signals transmitted toward the central nervous system, in this case from the gastrointestinal tract, via the vagus nerve.
a role in reducing further food intake. Robert Margolskee of the Monell Chemical Senses Center described scientists’ discovery of taste-signaling proteins in the gut in the 1990s and what has been learned since then about which gut cells in particular express the taste receptors and how gut-expressed taste proteins contribute to the physiological response to food. Robert Ritter of Washington State University elaborated on some of the information and ideas presented by Moran and explored in greater mechanistic detail how vagal signals activated by gut peptides, cholecystokinin in particular, contribute to the process of satiation and reduce further food intake. Finally, Laurette Dubé of McGill University considered the broader cognitive and social context within which brain-digestive system interactions operate and impact eating behavior. Chapter 2 summarizes these four speakers’ presentations and the discussion that followed.
Next, workshop participants explored two recently developed methodologies being used to study the impact of food and food cues on brain activity and eating behavior: (1) neuroimaging and (2) self-report questionnaires. Dana Small of Yale University and the John B. Pierce Laboratory summarized neuroimaging evidence indicating that food cues in the environment can trigger eating even in the absence of hunger. She also described data from rat studies suggesting that the underlying physiological mechanism appears to be a postingestive glucose metabolic effect, as opposed to something sensory. Hisham Ziauddeen of the University of Cambridge highlighted the many assumptions underlying neuroimaging studies on eating behaviors and urged caution when interpreting the study results. Ashley Gearhardt of the University of Michigan explained why and how she and colleagues developed the Yale Food Addiction Scale (YFAS) as a tool for identifying individuals who may be experiencing addictive-like responses to food. She reviewed studies associating addictive-like eating (as identified by the YFAS) with various factors (e.g., neural functioning, impulsivity) implicated in an addictive process. Charles O’Brien of the University of Pennsylvania discussed updates to the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5), criteria for substance use disorder (formerly “dependence”) and the challenge of applying DSM criteria originally developed for use with drugs to a substance like food. Chapter 3 summarizes these four speakers’ presentations and the discussion that followed.
Throughout the workshop, participants expressed varying opinions regarding how to interpret existing evidence from neuroimaging and self-report questionnaires and whether it is appropriate to characterize certain eating behaviors (or foods) as addictive. In the latter half of the workshop, an entire session was organized around counterpoint presentations on whether the drug and alcohol addiction model is appropriate for food. Nicole Avena of Mount Sinai School of Medicine and Peter Rogers of the
University of Bristol, respectively, argued for and against use of the addiction model with food. Chapter 4 summarizes the presentations and discussion that took place during that session.
Much of the workshop discussion revolved around how the brain processes two kinds of food-related signals: (1) satiety signals sent from the digestive system indicating fullness and (2) sensory signals triggered by food in the gut and food cues in the environment. In his concluding presentation, Edmund Rolls of the Oxford Centre for Computational Neuroscience hypothesized that an imbalance between these two systems may contribute to obesity, with sensory signals overriding satiety signals and overstimulating the reward system in the brain. Revisiting Dubé’s argument that eating behavior is influenced by the broader context in which the brain and digestive system operate, Rolls suggested that whether the two are imbalanced depends, in part, on “top-down” cognitive processes in the brain that influence how people actually perceive and respond to food rewards. A better understanding of individual differences in sensitivity to food rewards and whether greater sensitivity may contribute to obesity is one of several topics Rolls suggested for future research. Chapter 5 summarizes Rolls’s concluding presentation, the concluding panel discussion that followed, and the discussion of strategies for future research.
