Psychologist Brad Bushman holds a voodoo doll used in an experiment to see how blood sugar levels changed people’s view about their spouse. Volunteers with lower levels of blood sugar stuck more pins in voodoo dolls of their spouses than people with higher levels. (Jo McCulty/The Ohio State University)

Serious discussions between spouses shouldn’t take place on an empty stomach, a study suggests.

Husbands and wives reported being most unhappy with their spouses when their blood-sugar levels were lowest, usually at night, according to findings published last week in the Proceedings of the National Academy of Sciences. Missing a meal, dieting or just being hungry may be the reason, researchers said.

Sugar, or glucose, is used as fuel by the brain to help regulate self-control. Without the fuel, it is more difficult for people to control such emotions as anger and aggression, researchers said. The findings are among the first to show how low blood sugar levels may play a part in marital arguments, confrontations and even domestic violence, said the study’s lead author, Brad Bushman of Ohio State University,

In the study, 107 married couples tested their blood-sugar levels before breakfast and before bed. They were also given voodoo dolls representing their spouses and told to insert as many as 51 pins daily depending on how angry they were with their partner.

Those with the lowest nighttime blood-sugar levels inserted the most pins, the study found. Women tended to stick more pins into their voodoo dolls than men did, but the difference wasn’t significant.

After 21 days, the couples went into a laboratory, where they were told they would compete with their spouse to see who could press a button the fastest to test aggressive behavior. The winners could blast their spouse with a loud noise through headphones. In reality, the spouses were playing against a computer. Those with the lowest average nighttime blood-sugar levels sent louder and longer noises to their spouse.

“If couples have a sensitive topic to discuss, it would be really smart to do it over dinner or, better yet, after dinner,” Bushman said. “They should definitely not do it on an empty stomach.” Low blood sugar can trigger hormones that cause people to become more aggressive, anxious and irritable, said Timothy Graham, an assistant professor of medicine at the University of Utah, who wasn’t involved with the study.