Opiates, overeating and obesity: a psychogenetic analysis.

OBJECTIVE: This study provides an original perspective on the associations among endogenous opiates, overeating and obesity. The aim was to assess whether variability in the OPRM1 gene, as assessed by seven single-nucleotide polymorphisms, relates to individual differences in the preference for sweet and fatty foods. We also anticipated that these food preferences would be positively associated with binge eating, hedonic eating and emotionally driven eating-patterns of overeating that would, in turn, predict higher body mass index (BMI). DESIGN: Analysis of variance procedures examined genotype differences in food preferences; bivariate correlation coefficients examined the relationships among food preferences and the overeating variables; and a regression analysis tested the combined influences of the overeating variables on BMI. DNA was extracted from whole blood for the genotyping, and measures of food preferences and eating behaviours were obtained from well-validated self-report questionnaires. SUBJECTS: Participants were 300 healthy adult men and women recruited from the community. RESULTS: All the predicted associations were supported by statistically significant results. In particular, the G/G genotype group of the functional A118G marker of the OPRM1 gene reported higher preferences for sweet and fatty foods compared with the other two groups. Food preferences were also related to all overeating measures, which in turn accounted for a substantial proportion of the variance in BMI. CONCLUSIONS: Our findings suggest that some of the diversity in the preference for highly palatable foods can be explained by genotypic differences in the regulation of mu opioid receptors. The associations reported in this paper are important from a public-health perspective because of the abuse potential of sweet-fat foods and their strong relationship with obesity.

Food Aversion Learning by the Hermit Crab Pagurus granosimanus.

The common intertidal hermit crab Pagurus granosimanus learns in one or two trials to reject an attractive, novel food (beef) when illness is induced by lithium chloride injected one hour after the animal accepts and eats the beef. Crabs fed a familiar food (fish) before lithium chloride injection do not learn to avoid the fish. Nor do they learn to reject beef when injected with a sodium chloride solution, or when punctured with a hypodermic needle one hour after their first and second beef meals. Because many crustaceans are scavengers and generalist feeders, they must commonly encounter a wide variety of toxic foods. Quickly acquired and long-lasting aversion to a new food eaten a few hours before the onset of a serious physiological upset could cause these animals to avoid such hazardous foods in the future. Food aversion learning has never before been reported in a crustacean.