With an elaborate series of pudding taste tests, a new Yale study brings doctors one step closer to understanding why patients with chronic pain are at a higher risk for obesity.

Researchers at the School of Medicine and Yale-affiliated John B. Pierce Laboratory found that for patients with chronic low back pain (CLBP), there was no link between how much they liked the pudding and how much they ate. While prior research has shown that CLBP affects select circuits of the brain important in pleasure, this study shows how these changes manifest in eating behavior. The findings may change the way doctors treat patients with CLBP, said Paul Geha, lead author and psychiatry resident at Yale School of Medicine.

“The study shows that both food preferences and satiety are abnormal in chronic pain patients,” said Vania Apkarian, pain researcher at Northwestern University who was not involved with the study. “This is the first psychophysical study showing that there is a real physiological basis regarding the propensity of these subjects to become obese.”

The study, comprised of patients with CLBP as well as healthy subjects, was divided into two sessions. During the first session, all subjects were asked to rate a set of puddings with different fat contents, judging various factors like creaminess, intensity, sweetness and fattiness, as well as how much they liked each pudding. To ensure that changing satiety levels would not affect the ratings, subjects were asked to taste, but not ingest, each sample.

The team found that ratings of creaminess, fattiness and other sensory attributes were indistinguishable among healthy and CLBP subjects. However, the CLBP patients consistently found the puddings less likable.

“Patients weren’t more or less sensitive to sweetness or fat content,” said Barry Green, director of the John B. Pierce Laboratory and one of the study authors. “[Instead], they didn’t seem to get the same hedonic satisfaction.”

In the second part of the experiment, researchers set out to determine whether the pudding’s perceived likability from session one would affect how much of it a subject ate. Subjects were instructed to eat as much pudding as they wanted, rating their hunger levels before and after.

In healthy subjects there was a strong correlation between how much they liked the pudding and how much of it they ate. As expected, those who ate more pudding also experienced a larger drop in hunger levels. In CLBP subjects, both of these relationships were missing. Neither subjective enjoyment of the pudding nor a change in hunger levels controlled how much the CLBP patients ultimately ate.

Researchers propose that this disruption is a risk factor for overeating and obesity, since pleasure typically dictates how much people eat. While this study did not probe brain mechanisms responsible for the uncoupling of pleasure and consumption, previous research suggested dysfunction in the ventral striatum and medial prefrontal cortex circuit, a loop central in processing reward.

While pain and feeding behavior seem unrelated at first glance, Geha said that recognizing this connection between CLBP and obesity is a key step for treating patients with recurring back pain. For instance, he suggested working with CLBP patients to determine their individual risks for obesity, and also stressed the importance of prevention.

“We should treat [CLBP] patients not simply as patients suffering from back pain, but as patients who have a predisposition to other morbidities, like obesity,” Geha said.

While the experiment only included patients with more than two years of CLBP, for future studies Geha plans to enroll newly diagnosed back pain patients. Researchers would then be able to monitor their feeding behavior, body weight and back pain over an extended period of time.

Chronic pain affects 116 million Americans each year and is the most common cause of long-term disability.