How Does Chronic Pain Change Eating Behaviors?

Studies have shown that people often experience chronic pain and obesity together, though the exact reasons are still unclear. Evidence has suggested that obesity is common in chronic pain patients, while people affected by obesity tend to report higher levels of pain.

A team of neuroscientists examined this connection further in a recent study. They suggested that changes to the brain’s limbic system—an area associated with emotions and decision making—may contribute to obesity prevalence in chronic pain patients.

The nucleus accumbens, a structure in the brain that mediates between motivation and decision-making, could have major impact on the eating behaviors in chronic pain patients, according to Paul Geha, MD, an assistant professor of psychiatry at the University of Rochester and lead author of the study.

In 2014, Geha studied the role of nucleus accumbens in how patients with chronic lower back pain digest food. He found that the patients’ calorie intake were not guided by food pleasure or hunger. Some patients continued to eat high-fat foods and sugary drinks even if they weren’t enjoyable.

Geha and his team took those findings a step further for the new study. They examined the relationship between pleasure pathways and eating behaviors in patients before they developed chronic pain.

The researchers recruited 43 patients with chronic lower back pain, 51 patients with subacute back pain, and 36 patients who had no back pain.

“We’re interested in trying to determine whether we can find a biological marker for chronic pain before it sets in,” Ivan de Araujo, PhD, a professor of neuroscience at the Icahn School of Medicine at Mount Sinai and co-author of the study, told Verywell.

Participants were told to arrive neither hungry nor full on the first day. They were given a variety of pudding and Jell-O samples to taste and asked to rate how much they liked each sample. On the second day, participants came in hungry and were fed macaroni and cheese. Then they were given the pudding that had the highest rating and told to eat as much as they wanted.

Finally, the participants had an MRI scan so the researchers could further study the parts of the brain that are associated with pain and pleasure signals.

“We expected the patients who would be at risk, or become persistent at the end, to have the same picture as the patients who were chronic,” Geha said. He had a theory that since pathways in the brain that are important for pleasure perception and pain intersect, pain patients might develop disrupted eating behaviors early on.

“The picture was actually not like that,” he said. “What happened was a bit of both. In the subacute phase, only the patients who recovered later on showed disrupted eating behavior. They were exactly like the chronic pain patients.”

The data suggested that a change in nucleus accumbens only happened when the pain became chronic.

“The system that tells the brain you had enough food or enough calories changes because of pain. And we are trying to argue that these changes are related to the effect of pain on the reward circuitry,” de Araujo said. “The way things relate to each other is very complicated and it shows the problem is very complex.”

Limitations and Future Studies

Despite the findings, it might be too soon to draw any conclusion between chronic pain and obesity. This study had a relatively small sample and only focused on one type of chronic pain. The participants were asked to self-report their levels of hunger and fullness, which could have been misreported.

“There are a lot of cognitive factors that influence the way people communicate with the experimenter,” de Araujo said. “But all in all, we can still grab some significant differences between the groups assuming these biases are pervasive across subjects.”

Researchers are planning to focus future studies on patients with fibromyalgia, migraines, and knee arthritis.

"I would think that different chronic pain conditions might have different ways of experiencing foods and maybe different types of disruptions," Geha said.