Australasian Science Magazine

By Magdeline Lum

Lower levels of blood sugar make us more likely to lash out, and the people we lash out at are often those we hold closest to our hearts.

A study from Ohio State University has found that lower levels of blood sugar makes married people angrier at their spouse and are more likely to lash out aggressively. The good news is that blood glucose levels can be increased quickly by eating carbohydrates or sugary foods.

The 3-year study involved 107 married couples. Their general satisfaction for their relationship was assessed using a survey that asked each spouse how much they agreed with statements like “I feel satisfied with our relationship”. Over 21 days, each couple monitored their blood glucose levels in the morning and evening.

The couples were also given a voodoo doll each with 51 pins. Each spouse was instructed to stick the pins in the doll to represent their level of anger towards their partner. This activity was done away from the presence of their spouse.

The lower the participants’ evening blood glucose levels, the more pins they stuck in the voodoo doll representing their spouse. This association was present even after the researchers took into account the couples’ relationship satisfaction.

“When they had lower blood glucose, they felt angrier and took it out on the dolls representing their spouse,” Prof Brad Bushman said. “Even those who reported they had good relationships with their spouses were more likely to express anger if their blood glucose levels were lower.”

It was not just the dolls who took the brunt of the anger. After the 21 days, the couples came into the laboratory to take part in an experimental task. They were told they would compete with their spouse to see who could press a button faster when a target square turned red on the computer. The winner on each trial could blast his or her spouse with loud noise through headphones.

In reality, though, they weren’t playing against their spouse – they were playing against a computer that let them win about half the time. Each time they “won”, the participants decided how loud of a noise they would deliver to their spouse and how long it would last. Their spouses were in separate rooms during the experiment, so participants didn’t know they weren’t really delivering the noise blast.

“Within the ethical limits of the lab, we gave these participants a weapon that they could use to blast their spouse with unpleasant noise,” Bushman said.

The results showed that people with lower average levels of evening glucose sent louder and longer noise to their spouse, even after controlling for relationship satisfaction and differences between men and women. When these results were combined with the results from the voodoo doll task, those who stuck more pins in the voodoo doll were more likely to deliver louder and longer noise blasts.

“We found a clear link between aggressive impulses as seen with the dolls and actual aggressive behaviour,” Bushman said.

Bushman said that glucose is fuel for the brain. The self-control needed to deal with anger and aggressive impulses takes energy, and that energy is provided in part by glucose.

“Even though the brain is only 2% of our body weight, it consumes about 20% of our calories. It is a very demanding organ when it comes to energy,” he said.

Bushman has simple advice for anyone in a relationship about to have a difficult discussion: do not go in hungry.