Chances are that low blood sugar – and not your significant other – is to blame for your angry mood, according to a study published online in the Proceedings of the National Academy of Sciences.
The study found that married people's blood-glucose levels predicted how aggressive they would be with their spouse, measured by pins in a voodoo doll and the urge to blast loud noises into a partner's ear.
Spouses with low blood sugar got "hangry" (hungry and angry) regardless of whether they were happily married, said lead author Brad Bushman, professor of communication and psychology at Ohio State University.
"We found that being hangry can affect our behaviour in a bad way, even in our most intimate relationships," he said.
Bushman and colleagues recruited 107 married couples, and asked each participant to fill out a relationship satisfaction questionnaire. They measured participants' blood-glucose levels each night, capturing dips in blood sugar about five hours after supper.
Then came the voodoo dolls.
Participants were given 51 pins and encouraged to take out their frustrations on a small stuffy that stood in for their spouse.
At the end of each day, for three weeks straight, participants stabbed the doll with 0 to 51 pins, depending on how ticked off they were, and recorded the number of pins stuck in the doll each night. The voodoo ritual was done in secret, away from the hapless mate.
The researchers found a direct relationship between low blood-glucose levels and the number of nightly "stabbings."
The association remained even after researchers accounted for differences in marital satisfaction, although people with lower-quality relationships were more vicious with the doll, Bushman said.
The study suggests that hunger caused by low blood-sugar levels may play a role in marital arguments – and possibly even domestic violence, he said.
Still not convinced? Check out the second part of the study.
In this phase, spouses were separated into different rooms and duped into thinking they could blast their mates with loud noise through headphones using (mock) audio controls.
Once again, the researchers found that participants with lower glucose levels sent louder and longer blasts to their spouses.
Those who were angry enough to try to burst their partners' eardrums were also more likely to have stuck the most pins in the voodoo dolls. (No actual eardrums were harmed in the sham setup.)
The researchers did not look at late-evening fatigue as a factor in the aggression, since fatigue is often related to low blood-glucose levels, Bushman said.
One explanation for the hangry-spouse phenomenon is that glucose feeds the brain, which consumes about 20 per cent of our calories.
Keeping aggressive impulses in check requires self-control, which is harder to maintain with a drop in blood-glucose levels, Bushman explained.
Previous research has shown that people with diabetic symptoms tend to be more aggressive and less forgiving than others, he added.
Together, the studies highlight the virtues of a late-night snack. After all, simple carbohydrates are way cheaper than marriage counselling.