The hormone ghrelin, which has been described as the hunger hormone, has a large influence over eating behaviors, as it sends messages to the brain that signal feelings of hunger. Ghrelin levels rise when we haven’t had enough to eat, but new research from the latest issue of Nature Neuroscience indicates that this chemical also increases during times of stress. Using mice, researchers from the University of Texas Southwestern Medical Center found that in addition to stimulating appetite, ghrelin may also reduce the amount of symptoms brought on by stress.

The researchers experimented with ghrelin’s effect on mood and behavior using two groups of mice, one comprising normal mice and the other formed of mice genetically altered to not respond to ghrelin. First, they limited the amount of food the normal mice could eat, which, over the course of ten days, caused a four-fold increase in their ghrelin levels. Compared to control mice, these mice displayed fewer signs of depression and anxiety when exposed to mazes and other trials meant to induce these behaviors. The researchers then conducted the same experiment with the genetically altered mice, finding that these mice were not less anxious or depressed than controls. Next, they examined ghrelin’s relationship with chronic stress by putting both groups of mice in daily contact with highly aggressive mice. While this situation caused increases in the ghrelin levels of all of the mice, the genetically altered mice displayed more severe socially-inhibited behavior and also ate less food, an indication that ghrelin caused a reduction in the stress-related symptoms experienced by normal mice.

There may be many factors explaining the observed anti-depressant qualities of ghrelin, as the researchers explain. Taking an evolutionary viewpoint, they surmise that the ability to remain calm during times of hunger and famine would help early humans to hunt food and avoid predators. Although this effect may have originated as a survival strategy, in today's world, it could be the reason why some people overeat when anxious or depressed. Moreover, this study may point toward a new way of thinking about hunger and the biological processes that control this basic need. Ghrelin may impact more than just eating behavior, a fact that Dr. Michael Lutter, head author of the study, discussed in a press release: “Our findings support the idea that these hunger hormones don’t do just one thing; rather, they coordinate an entire behavioral response to stress and probably affect mood, stress and energy levels.”

Further study of ghrelin and other related factors could give crucial insights into eating behaviors, especially with regards to obesity, and will hopefully point toward effective ways to treat this condition. While past research has indicated that blocking ghrelin may aid weight loss, this study has shown that doing so could result in unintended effects on mood and behavior, and we must continue to focus on this hormone to better clarify its role. By learning of the mechanisms through which stress can harm the body and contribute to weight gain, we will have a better understanding of how to reduce its effects and improve the overall health of many individuals.