Eating Disorders and Chronic Pain: A Complicated Relationship

Chronic pain and eating disorders may occur together but too few clinicians are aware of the association, according to experts who have studied the comorbid conditions. Recognizing that both conditions may occur together, along with knowing which questions to ask, can go a long way toward providing better care, said those who have researched the relationship.

Central sensitization, wherein the CNS becomes provoked into a persistent state of heightened reactivity and lowers a person’s sensitivity threshold, is thought to be in involved in the development of chronic pain. And “having a chronic medical condition and, in particular, chronic pain, greatly increases your chance of developing an eating disorder,” said Dr. Sim.

In these instances, does the pain or the eating disorder come first? That’s difficult to say, Dr. Sim told PPM.

“It’s very common to avoid eating if it gives you pain,” she explained, such as having a gastrointestinal issue that flares if you eat certain foods. In other cases, an individual may be on a chronic pain medication known to be linked with weight gain, such as gabapentin and pregabalin.² With the weight gain can come disrupted eating patterns. If they gain a substantial amount of weight in a short time, many patients will restrict their eating.

Dr. Sim’s research and clinical experience, primarily focused on teens and young adults, suggest that of all adolescents and young adults with chronic pain, 20% have formal eating disorder diagnoses. And 80% of those with postural orthostatic tachycardia syndrome (POTS) have clinically significant disordered eating or weight loss.

Dr. Sim’s review of current research suggests those with chronic pain and those with eating disorders share some unique temperamental traits and demographics. For instance, both conditions are more common in females. Those with chronic pain and with restrictive eating issues share certain temperamental characteristics, such as anxiety and harm avoidance. People with chronic pain and eating disorders both tend to worry, self-criticize, and be emotionally negative.

Additional research by Paul Geha, MD, assistant professor of psychiatry at the University of Rochester Medical Center, has focused on back pain and eating disorders.³ His team found that the brain area responsible for motivation and pleasure — the nucleus accumbens — is impacted when someone experiences pain.

“Our research suggests that having low-back pain will increase the susceptibility to overeating,” he said. His team evaluated 43 people with chronic low back pain, 31 with subacute back pain, and 36 healthy controls. They looked at these subjects’ responses to sugar and fat. None of the subjects had eating behavior changes with sugar, but they did with fat. The individuals with chronic low back pain reported that foods high in fat became problematic for them over time. Dr. Geha said this is often unrelated to weight gain and presumably related to brain plasticity.

Dr. Geha’s team conducted brain scans to look at the volume of the nucleus accumbens in the subjects. The disrupted eating that set in after pain chronification was accompanied by structural changes in the nucleus accumbens. In previous research by Dr. Geha, his team found that people with chronic low back pain, compared to healthy controls, reported lower rating of food pleasure when eating fatty puddings but nevertheless continued to eat them.⁴ Dr. Geha concluded that the change in liking the food did not alter caloric intake, thus helping to explain the link between chronic low back pain and overeating.

Having conversations with patients with suspected eating disorders can be difficult, especially when it is not the physician’s specialty, as Dr. Sim noted. She suggests asking about body image and body weight with questions such as: “Are others concerned?” “Do others try to make you eat?” Do they get mad when you don’t?”

Another approach, she said, is simply to say (if a clinician is unsure): “I don’t know if you have an eating disorder, but I know your weight is too low.” Dr. Sim will often give a patient in this type of case a 3,000 calorie-a-day diet and instruct them to follow it for 1 month. She tells them: “If you can do that, we know you don’t have an eating disorder. If not, we need to get you help.”