In The Physiology of Willpower: Linking Blood Glucose to Self-Control (Gailliot and Baumeister) (local copy: PDF) the authors look at the effect that exerting one’s willpower has on blood glucose levels. There are some pretty strong connections between glucose tolerance and antisocial behaviour:
Several other studies have shown that improving the diet of incarcerated adolescents or adult prisoners reduces the incidence of violence in prison (e.g., “New Studies Show Strong Link,” 2004). It is plausible that the reduction in prison violence by improved diet is partially attributable to improved glucose levels or glucose tolerance.
A remarkable longitudinal field study of criminal recidivism by Virkkunen, DeJong, Bartko, Goodwin, and Linnoila (1989) sought to predict violent criminal acts over several years after release from prison. It found that glucose tolerance correctly predicted further violence for 84% of criminals. In view of the many extraneous variables and error variance in measuring criminal behavior, it would be hard to ask for a stronger result. Prisoners who exhibited poor glucose tolerance were much more likely to commit violent acts years later as compared to prisoners with better glucose tolerance. This relationship did not appear to be attributable to any other relevant physiological or demographic factors. That glucose tolerance at one point predicted violent acts at a later point is consistent with the interpretation that poor glucose tolerance partially caused the violent acts. Individuals who exhibit poor glucose tolerance as a stable trait seem predisposed to behave violently when opportunities beckon.