Abstract: 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.
Discussion
This is the first study that investigates the role of short-term energy dynamics, BMI status and their interactions on individuals’ ability to refrain from lying. We found that only a fraction of subjects (specifically, lean females) becomes more honest after consuming breakfast. Major differences in behaviour are instead found between lean and obese subjects, especially under satiation. Such results provide limited support for an effect of short term energetic shifts on moral decision making. Importantly, they reject H1 in favour of H2, as energy dynamics alone cannot explain the observed differences in unethical behaviour. These findings complement the analyses of the economic, psychological and cognitive determinants of small-scale dishonesty. A growing body of research has started to identify the psychological factors underlying unethical behaviour25,42,43, often opposing alternative views about how the integrity of cognitive functions (in particular, self-control) affects the ability for refraining from lying. For example, it has been shown that people are more likely to lie under conditions of reduced self-control29,30,42, while resisting the temptation both requires and depletes self-regulatory resources25. Similarly, sleep-deprivation and time pressure have been shown to increase the likelihood of engaging in unethical behaviour in both work-related27 and lab settings28. Overall, our results fail to support the hypothesis that glucose acts as a general modulator of self-control resources underlying honest behaviour, as obese subjects cheat more despite higher blood glucose levels.
In our study, lean female subjects become more honest when sated, but males fail to do so. Increasing evidence of sex differences in the neural activity related to hunger and satiety44,45 and in cortical areas processing food-related stimuli46,47 supports the hypothesis that women are more sensitive to food-related cues than men and may have a greater sensitivity to humoural signals of hunger and satiation48. Similarly, a heightened malleability and sensitivity of women’s preferences to the context of an experiment has been suggested to explain gender differences in some economic games49. Given the overlap of brain areas (e.g., orbifrontal cortex) involved in processing food rewards and money rewards50,51,52 and evidences showing the reciprocal association between the incentive value of food and of money53, we suggest that a higher sensitivity of women to energetic shifts could facilitate the substitution of a primary reward (e.g., the calories provided by the food) to a secondary reward obtained at the moral cost of lying (e.g., the extra money earned by over-reporting the die outcome). Alterations of physiological state (e.g., hunger) have been suggested to modulate the emergence of gender gaps in economic behaviour54. In line with that, our finding can help interpret the contrasting results on gender and honesty in the past literature55,56,57,58,59.
Major differences in lying behaviour emerge between obese and lean subjects especially after breakfast consumption. Such finding suggests that obesity may be associated to a reduced sensitivity to short-term energetic shifts. In support of this interpretation, it has been shown that the brain’s ability to respond to alterations in glucose metabolism becomes aberrant in both individuals predisposed to become obese (obesity prone) and those already obese and diabetic60. Moreover, while fluctuations in the motivational value of food are thought to contribute to the control of eating behaviour, there is evidence that such processes are impaired in individuals with obesity. For example, Castellanos and colleagues40 show that while lean and obese have similar attentional bias to food-related cues when hungry, obese but not lean keep a high attentional bias even after eating, possibly due to a reward system dysregulation. In support of it, sensitivity to reward devaluation decreases with increasing BMI61. As dishonest behaviour has been linked to heightened responses in specific reward-related brain areas (e.g., nucleus accumbens62), obese subjects’ inability to correctly devaluate rewards in post-meal contexts may possibly contribute to explain the observed levels of dishonest behaviour.
Investigating the nature of lies can help us better characterize the motivations behind dishonest behaviour. We found that obese people’s misreporting behaviour is mainly motivated by the willingness to avoid the lower payoff in the die task. This could be related to loss aversion63, echoing studies showing differential neural responses of obese subjects to monetary losses and to the anticipation of such losses compared to lean people64. If loss aversion is a permanent trait, then it might not be surprising that the estimated percentage of lies to avoid the lower payoff remains the same regardless of their metabolic state. In contrast, the willingness to maximize one’s payoff and the willingness to avoid the lowest payoff have a more similar weight in lean subjects.
Due to the correlational nature of our study, we are not able to infer causality between obesity and moral behaviour. Obesity stems from a complex interaction between behavioural, neuronal and metabolic processes and is associated (but not necessarily causally) to a dysregulation of the mechanisms governing energy homeostasis. In support of this view, recent genetic studies concluded that obesity is less metabolic and more driven by neuro-behavioural disorders65. From an evolutionary perspective, it has been suggested that insulin resistance, a metabolic condition often associated to obesity and type-2 diabetes, might have evolved as a socio-ecological adaptation allowing a shift from muscle-dependent to brain-dependent life strategies, and that the pathological consequences of obesity are likely to be caused by immune chronic inflammation rather than by changes in the homeostatic regulation system66. These studies challenge traditional views supporting the metabolic origins of obesity67 and suggest a more intertwined role of social, hormonal and immunological factors in the emergence of obesity. Given the literature, we may postulate that the same behavioural patterns associated with obesity might be responsible for the observed variation in dishonest behaviour. Importantly, this suggests that although energy shifts might impact honesty, results cannot be explained by energy dynamics alone.
Finally, our study adds novel findings to the growing literature exploring the cognitive and economic determinants of unethical behaviour, and calls for a deeper understanding of the intertwined neurological, physiological and socio-economic factors that shape our ability to comply with moral norms.
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