I recently read this description of the effects of low blood sugar on aggressive behavior. Basically, exercising self control of any kind requires a lot of glucose; if you don't have glucose available, then you aren't able to be self controlled. This means you behave badly: you can't pay attention well, you become impulsive, you cope less well with stress, and you commit more crimes.
One study found 90% of the juvenile delinquents in custody had low blood sugar. Another found that by looking at the blood sugar of recently released criminals, researchers could predict with 80% accuracy who would go on to re-offend.
Having a snack (especially the sugary kind) is the best way to restore one's glucose levels and thus give yourself willpower. Americans have gotten fatter in recent years because they eat too much, consuming massive quantities of sugar (over 150 pounds annually for every man, woman and child!). Usually this is seen as a public health problem, and articles regularly appear discussing the evils of sugar. But maybe this is all wrong: by consuming so much sugar, we may be fat, but we are also more productive, peaceable, and disciplined.
A new public service message: Eat sugar and reduce crime?