Having low blood glucose means you are more likely to stick pins in a voodoo doll that represents your spouse, a new study suggests.
And you are more likely to blast your spouse with a loud unpleasant noise - given the chance, finds a study published this week in the Proceedings of the National Academy of Sciences.
The findings could point to a previously unrecognized contribution to aggression between married couples, says lead author Dr Brad Bushman, a professor of communication and psychology at Ohio State University in Columbus.
Preventing aggressive behavior relies on self control, which is governed by our pre-frontal cortex, says Bushman.
Self control requires energy, part of which comes from glucose.
"It's widely accepted that glucose boosts self control," said Bushman.
On the contrary, when our brain doesn't get enough glucose, we can get cranky -- something most of us can attest to from personal experience.
Voodoo doll experiment
Bushman and colleagues previously showed that glucose was linked to control of anger in a short-term lab experiment involving interactions between strangers.
But everyone knows we are most likely to snap at people we're closest to. So in their latest study, Bushman and colleagues studied interactions between married couples in their own home, over a much longer time frame.
For 21 days, 107 couples had their blood glucose tested daily and just before each glucose test they got the opportunity to express aggression towards their spouse.
They were given a voodoo doll that represented their spouse and told they could stick up to 51 pins in the doll, depending on how angry they felt with their other half.
"People with lower glucose stabbed more pins in the doll than people with higher glucose," said Bushman.
People whose glucose levels were in the lowest 25 percent put over twice as many pins in the doll as people whose glucose levels were in the top 25 percent.
After the 21 days, the couples then took part in a lab experiment in which they competed with their spouse in a computer game -- they had to see who could press a button fastest when a target square turned red.
The winner of each of the 25 trials was once again given an opportunity to express their aggression towards their partner.
This time, they were allowed to blast the losing spouse with up to 5 seconds of an extremely unpleasant noise up to 105 decibels loud. The noise was the combined sound of a smoke alarm, dentist's drill and fingernails scratching down a blackboard.
The researchers found people's average glucose level -- calculated from the 21-day study -- had an influence on what happened.
"People with low glucose gave their spouse louder and longer noise blasts," said Bushman.
He says the study controlled for relationship quality.
"Hungry people are cranky and aggressive even if they have a good relationship with their spouse," said Bushman.
The study had its challenges including getting participants to agree to prick themselves for glucose testing twice a day.
Bushman says he also got a phone call from his credit card company after he bought some key experimental equipment.
"I got a telephone call and they said 'We've never seen anyone spend $5,000 on voodoo dolls before so we were a little suspicious and though we might check it out," said Bushman, who won an Ig Nobel prize last year for a study that showed people think they are more attractive when drinking alcohol.
But the study, funded by the National Science Foundation, has a serious side.
"I think the implications are pretty broad," said Bushman.
"What we eat is related to our angry feelings and aggressive behaviors towards our most intimate partners."
Bushman's recommendation: "If I was going to have a serious discussion with my spouse, I'd make sure I wasn't hungry first."
This article originally appeared on ABC Science Online.