That coworker who'll lay into you if they skipped breakfast? New research suggests his metabolism is partly to blame.
Researchers from the University of Guelph have shown that a sudden drop in glucose -- such as we experience when we're hungry -- can have a dramatic impact on our mood. The findings help explain why so many people bemoan getting "hangry".
Food fight
"We found evidence that a change in glucose level can have a lasting effect on mood," said coauthor Francesco Leri, a professor at the university's Department of Psychology.
"I was skeptical when people would tell me that they get grouchy if they don't eat, but now I believe it. Hypoglycemia is a strong physiological and psychological stressor."
For the study, the team worked with a group of lab rats, following their emotional behavior after inducing hypoglycemia (low blood-sugar levels). The group was injected with a glucose metabolism blocker -- which artificially induced hypoglycemia -- and was placed in a special chamber. The same rats later received an injection of water and were placed in a different chamber.
At the end of the trials, the rats were allowed to enter one of the chambers -- and actively avoided the one where they experienced hypoglycemia.
"This type of avoidance behaviour is an expression of stress and anxiety," said Leri. "The animals are avoiding that chamber because they had a stressful experience there. They don't want to experience it again."
The team took blood samples of the rats at various stages during the experiment and report that rats showed higher blood levels of corticosterone, an indicator of physiological stress, following the first step of the trial. In other words, they were likely experiencing acute stress while their blood-sugar levels were artificially lowered to mimic skipping a meal or two.
The rats also appeared more sluggish when given the glucose metabolism blocker. While it may be argued that this effect stems from a lack of glucose in the rats' systems -- muscles use glucose as fuel -- the team reports that this doesn't seem to be the case. When the sluggish rats were given antidepressant medication, "the sluggish behavior was not observed. The animals moved around normally,” Leri explained.
"This is interesting because their muscles still weren't getting the glucose, yet their behaviour changed."
"This is interesting because their muscles still weren't getting the glucose, yet their behaviour changed."
Overall, the findings support the idea that animals (us humans included) experience anxiety and a sour mood when going hungry for too long. The results may help flesh out our understanding of the treatment dynamic for those who experience anxiety or depression. They may also shed some light on the (still poorly-understood) link between depression and diseases such as obesity, diabetes, and eating disorders.
"When people think about negative mood states and stress, they think about the psychological factors, not necessarily the metabolic factors," said PhD student Thomas Horman, who led the study. "But we found poor eating behaviour can have an impact."
"The factors that lead someone to develop depression and anxiety can be different from one person to the next. Knowing that nutrition is a factor, we can include eating habits into possible treatment."
Next, the team plans to determine whether long-term hypoglycemia may be a risk factor for developing depression-like behavior. While a single missed meal may make us grumpy, doing so constantly may have a dramatic impact on our mood and quality of life:
"Poor mood and poor eating can become a vicious cycle in that if a person isn't eating properly, they can experience a drop in mood, and this drop in mood can make them not want to eat," Horman explains.
"If someone is constantly missing meals and constantly experiencing this stressor, the response could affect their emotional state on a more constant level."
The paper "An exploration of the aversive properties of 2-deoxy-D-glucose in rats" has been published in the journal Psychopharmacology.
