Scientists have found that blood glucose levels can stimulate or restrain interest in high-calorie food, but that this regulatory mechanism may be lost in the context of obesity. Normally, the body strives to keep blood levels of glucose, the main cellular energy source, within a tight range. In healthy individuals, a transient drop in blood glucose levels, or hypoglycemia, stimulates hunger and food seeking behavior, whereas eating a meal restores blood glucose levels to a normal range (“normoglycemia”) and satiates hunger. However, not just any food will do—during mild hypoglycemia, people preferentially seek out foods high in sugar and fat. The brain is central to many mechanisms driving feeding behavior, but the precise brain pathways driving the motivation to consume high-calorie foods have not been known, nor whether there are differences between obese and non-obese individuals.
In the current study, researchers investigated whether mild hypoglycemia stimulates activity in parts of the brain linked to motivation and reward and if that activity is associated with desire for calorie rich foods. Using an imaging technology called functional magnetic resonance imaging (fMRI), the researchers examined changes in brain activity in obese and non-obese people as they were shown pictures of food. Participants viewed images of high calorie foods (e.g., ice cream), low-calorie foods (e.g., carrots), and non-foods first while in a normoglycemic state, then while in a mildly hypoglycemic state. As they viewed each image, participants were also asked to rate how much they liked and wanted the item they saw. When compared to their reactions during normoglycemia, people experiencing hypoglycemia showed greater activity in motivation and reward regions of the brain when viewing high-calorie foods, and their desire for them increased. In contrast, low-calorie food images did not provoke the same changes in brain activity and desire during hypoglycemia. Moreover, in non-obese participants, normoglycemia was associated with greater activity in brain regions that reduce motivation for rewarding stimuli—a response that was generally associated with lower desire for any of the foods. However, in obese individuals, this repressive brain activity was lost.
These findings not only help identify brain regions involved in food motivation, but also suggest that higher or lower blood glucose levels can influence susceptibility to high-calorie food cues in the environment—and that persons who are obese may be more susceptible, due to a loss of this regulatory response. While further research is needed, these findings also suggest that it may be possible to develop strategies to reduce desire for high-calorie food by minimizing hypoglycemia between meals.
Page KA, Seo D, Belfort-DeAguiar R, et al. Circulating glucose levels modultate neutral control for desire for high-calorie foods in humans. J Clin Invest 121: 4161-4169, 2011.