Reprinted from Eating Disorders Review
July/August Volume 26, Number 4
July/August Volume 26, Number 4
Two main components drive eating behavior: maintenance of energy balance (homeostatic eating), and the rewarding or pleasurable qualities of food (hedonic eating). Italian researchers have uncovered what may be a dysfunctional reward mechanism in a small study of 7 underweight and 7 weight-restored patients with anorexia nervosa (AN) (Am J Clin Nutr. 2015. 101:262).
Endocannabinoids are a set of naturally occurring brain substances that impact mood, learning, appetite, and brain plasticity. Food ingestion is periodically controlled by the endocannabinoid system. As Dr. Alessio Maria Monteleone and co-authors point out, in particular, hypothalamic and mesolimbic endocannabinoids are produced after food deprivation, and increase appetite by stimulating neurochemical pathways underlying both homeostatic and hedonic eating.
In an earlier study by the same researchers, hedonic eating in healthy subjects increased concentrations of ghrelin and 2-arachidpnoylglycerol, suggesting that these two markers modulated food-related reward (J Clin Endocrinol Metab. 2012; 97:E917). In the current study, the authors once again investigated the physiologic modulation of food-related reward, but this time studied patients with active AN and weight-restored patients with AN. The authors assessed peripheral endocannabinoid responses to hedonic eating in these patients, and compared these levels to those established in the previously studied healthy participants. Levels of other mediators were also measured, including two receptors whose activation, in opposition to that of cannabinoid-1, may reduce food intake and reward.
Patients with AN who were consecutively admitted to the eating disorder inpatient unit of Villa Garda Hospital, Naples, Italy, were screened for the study. All those selected for the study met DSM-IV criteria for past or present AN.
To test hedonic and non-hedonic eating, before the first session all participant were asked to indicate his or her favorite food, a food they would eat just for pleasure, even when full. Through a series of steps, including a 12-hour fast, the participants rated their hunger and satiety on a visual analog scale. Blood samples were dawn immediately after exposure to the favorite food and within 10 minutes after the individuals freely ate their favorite foods. In the second procedure, participants were exposed to a non-favorite food and had to eat an equivalent amount of it.
Surprisingly, in both hedonic and nonhedonic eating sessions, no significant difference emerged between groups in scores of hunger, satiety, urge to eat, or in the pleasantness of experiencing a mouthful of the presented food and the amount of food each participant would eat. In all groups, hunger and satiety scores before hedonic eating did not differ from those before nonhedonic eating, whereas scores for the urge to eat, pleasantness of experiencing a mouthful of the presented food, and the amount of food eaten were significantly higher before eating the favorite food than before eating the non-favorite food
When the authors compared the results from their study of underweight and weight-restored AN patients to earlier levels established from normal-weight healthy controls, they found altered plasma concentrations of 2-arachidonoyglycerol after hedonic eating in both groups of AN patients.
These results need to be replicated and extended, but they support the idea that responses of the endocannabinoid system to hedonic eating appear to be disturbed and may play a role in AN.