We’ve all known people who should have to wear a flashing red DANGER! sign if they miss lunch, though even without the warning we instinctively know to steer clear if someone is running on empty. A grumbling stomach means a drop in blood sugar, and through excruciating experience most of us realize that means trouble. But could the blood sugar-anger connection lurk behind more relationship conflicts than we realize?
A new study probed that question with a research methodology as painfully funny as it was effective. Researchers rounded up 107 married couples for a 21-day couples’ boot-camp to draw a direct line between blood glucose (aka circulating blood sugar) and aggression.
First they asked the couples to complete a relationship questionnaire that evaluated their level of satisfaction with their marriages, which allowed the research team to control for variables like how rocky the marriage was to begin with. They also measured all of the participants’ blood glucose levels to set a benchmark, and continued to measure the levels throughout the 21-day study.
The researchers predicted that drops in blood sugar would consistently correlate with heightened aggression between the spouses. Aggression was defined in two ways: aggressive impulse and aggressive behavior. The distinction was meant to identify aggression in thought versus action, because aggression rarely happens in a vacuum—there’s usually a thought impulse that precedes it, even if that impulse doesn’t occur immediately before the action but compounds over time.
To test aggressive impulse, the researchers gave participants a voodoo doll and 51 pins, with instructions to place as many pins in the doll every night as needed to show how angry they were with their spouse. A light conflict day might get just a couple pokes, while a “cover the kids' eyes and ears” day might warrant the full 51 to the head.
To test aggressive behavior, the researchers had the spouses wear headphones while they competed against each other in 25-part tasks. After each task, the winner decided how loudly and for how long to blast the loser with a noise through the headphones.
At the end of the 21 days, with riddled voodoo dolls and ringing ears aplenty, the hypothesis was proven out. The lower the level of blood glucose, the more pins the spouses poked, and the higher the intensity and longer the duration they blasted their partners through their headphones.
The study provides a couple of worthwhile takeaways. First, quoting Brad Bushman, professor of psychology and communication at Ohio State University and lead study author, “Before you have a difficult conversation with your spouse, make sure you're not hungry." Simple to say, harder to do.
Second, and the reason why that’s such good advice, is our brains are energy hogs. "Even though the brain is only two percent of our body weight, it consumes about 20 percent of our calories. It is a very demanding organ when it comes to energy," added Bushman. When the brain is short on energy, it’s also short on self-control, and the door is opened for aggressive impulses and behavior to take center stage. And if the study results are a true indication, we’re red lining our self-control more often than we realize.
I’d love to see a follow-up study that attempts to track these results against the blood sugar rollercoaster associated with fast food-laden diets. I have a suspicion that glucose-related aggression isn’t solely about how much or little food we eat, but also the sorts of food we eat. Just a hunch, but it stands to reason that shoveling in foods that cause our blood sugar levels to spike and crash day after day may also trigger spousal (and other) explosions. A little food for thought while you're sitting in the drive-thru.
The study was published in the Proceedings of the National Academy of Sciences.
You can find David DiSalvo on Twitter @neuronarrative, at his website The Daily Brain, and on YouTube at Your Brain Channel. His latest book is Brain Changer: How Harnessing Your Brain’s Power To Adapt Can Change Your Life.