Dishonesty is more affected by BMI status than by short-term changes in glucose.

There is evidence that human decision-making is affected by current body energy levels and physiological states. There is less clear evidence linking decision-making to long-term changes in energy, as those associated with obesity. We explore the link between energy, obesity and dishonesty by comparing the behaviour of obese and lean subjects when hungry or sated while playing an anonymous die-under-cup task. Participants performed the task either before or after breakfast. We find that short-term switches in energy have only a mild effect on dishonesty, as only lean females lie less when sated. By contrast, obese subjects lie more than lean subjects in both conditions, and they lie more to avoid the lowest payoff than to get the highest payoff. Our findings suggest that the observed patterns are more likely mediated by factors associated with obesity than by short term energy dynamics, and call for a better integration of the psychological, economic and biological drivers of moral behaviour.