A recent study finds that unhealthy eating behaviors at night can make people less helpful and more withdrawn the next day at work.

"For the first time, we have shown that healthy eating immediately affects our workplace behaviors and performance," says Seonghee "Sophia" Cho, corresponding author of the study and an assistant professor of psychology at North Carolina State University. "It is relatively well established that other health-related behaviors, such as sleep and exercise, affect our work. But nobody had looked at the short-term effects of unhealthy eating."

Fundamentally, the researchers had two questions: Does unhealthy eating behavior affect you at work the next day? And, if so, why?

For the study, researchers had 97 full-time employees in the United States answer a series of questions three times a day for 10 consecutive workdays. Before work on each day, study participants answered questions related to their physical and emotional well-being. At the end of each workday, participants answered questions about what they did at work. In the evening, before bed, participants answered questions about their eating and drinking behaviors after work.

In the context of the study, researchers defined "unhealthy eating" as instances when study participants felt they'd eaten too much junk food; when participants felt they'd had too much to eat or drink; or when participants reporting having too many late-night snacks.

The researchers found that, when people engaged in unhealthy eating behaviors, they were more likely to report having physical problems the next morning. Problems included headaches, stomachaches and diarrhea. In addition, when people reported unhealthy eating behaviors, they were also more likely to report emotional strains the next morning—such as feeling guilty or ashamed about their diet choices. Those physical and emotional strains associated with unhealthy eating were, in turn, related to changes in how people behaved at work throughout the day.

Essentially, when people reported physical or emotional strains associated with unhealthy eating, they were also more likely to report declines in "helping behavior" and increases in "withdrawal behavior." Helping behavior at work refers to helping colleagues and going the extra mile when you don't have to, such as assisting a co-worker with a task that is not your responsibility. Withdrawal behavior refers to avoiding work-related situations, even though you're at your workplace.

The researchers also found that people who were emotionally stable—meaning people who are better able to cope with stress because they're less emotionally volatile—suffered fewer adverse effects from unhealthy eating. Not only were emotionally stable people less likely to have physical or emotional strains after unhealthy eating, their workplace behaviors were also less likely to change even when they reported physical or emotional strains.

"The big takeaway here is that we now know unhealthy eating can have almost immediate effects on workplace performance," Cho says. "However, we can also say that there is no single 'healthy' diet, and healthy eating isn't just about nutritional content. It may be influenced by an individual's dietary needs, or even by when and how they're eating, instead of what they're eating.

"Companies can help to address healthy eating by paying more attention to the dietary needs and preferences of their employees and helping to address those needs, such as through on-site dining options. This can affect both the physical and mental health of their employees—and, by extension, their on-the-job performance."

The researchers also pointed to a variety of research questions that could be addressed moving forward.

"One confounding variable is that the way our questions were phrased, we may be capturing both unhealthy eating behaviors and unhealthy drinking behaviors related to alcohol," Cho says.

"That's something we will want to tease out moving forward. And while we focused on evening diet, it would be interesting to look at what people are eating at other times of day. Are there specific elements of diet that affect behavioral outcomes—such as sugar or caffeine content? Can there be positive effects of unhealthy eating, such as when people eat comfort foods to help cope with stress? This promises to be a rich field of study."

The study, "Does a Healthy Lifestyle Matter? A Daily Diary Study of Unhealthy Eating at Home and Behavioral Outcomes at Work," is published in the Journal of Applied Psychology.