The analysis of 68 studies found that almost one-quarter of obesity surgery candidates had a mood-related disorder, usually depression. Another 17 percent had binge-eating disorder, researchers report Jan. 12 in the Journal of the American Medical Association.
Obesity surgery, known medically as bariatric surgery, can be an option for people who are severely overweight -- typically 100 pounds or more.
And while doctors have known that patients often have mental health symptoms as well, it has not been clear just how common that is, said study author Dr. Aaron Dawes.
"What was striking to us is that depression and binge-eating disorder were both more than twice as common as they are in the general U.S. population," said Dawes, a general surgery resident at the University of California, Los Angeles.
The good news was that the review found no clear evidence that mental health conditions hindered patients' weight loss after surgery.
That's reassuring, Dawes said, because there have been some concerns about that possibility.
There are different forms of obesity surgery, but all generally alter the digestive tract to limit the amount of food a person can eat. Surgery candidates, Dawes noted, have to commit to a new way of eating, both to lose weight and stay healthy -- and there have been questions about whether people in poorer mental health can manage the post-surgery changes.
"This analysis does not support the notion that these patients do worse," Dawes said.
On the other hand, he added, the findings show how important it is to consider obesity surgery candidates' mental health.
"Doctors need to be aware that mental health conditions are common among these patients, and refer them for treatment if necessary," Dawes said.
It is standard for patients to have some sort of mental health screening before undergoing weight-loss surgery.
That's typically done by a mental health professional, who would then advise the surgery team on how to move ahead if the patient does have a psychiatric condition, said Dr. Bruce Wolfe, a bariatric surgeon at Oregon Health & Science University, in Portland.
"Mental health disorders are definitely prevalent among individuals with severe obesity, so that evaluation is important," said Wolfe, who was not involved in the study.
But, he stressed, a mental health diagnosis does not automatically disqualify someone from having surgery, as patients sometimes fear.
A person with moderate depression would be managed differently from someone having suicidal thoughts, for example, Wolfe said. The suicidal patient would not be a candidate for surgery; the depressed patient might have the procedure and receive depression therapy -- though there's still the question of whether that should happen before or after surgery, he noted.
As for binge-eating disorder, he said, it might seem like the condition would preclude people from obesity surgery, since they have to limit their food intake strictly.
But, as the current review shows, studies have found that people with the disorder fare as well as other patients, Wolfe said.
That might be partly because some get therapy for their binge-eating, Wolfe said. But he said the surgery also has effects on the nervous and hormonal systems that may help ease bingeing.
Based on the review, people with depression can also improve after surgery. Across seven studies, prevalence of depression dropped by anywhere from 8 percent to 74 percent after surgery. The severity of patients' depressive symptoms also fell -- by 40 percent to 70 percent.
"We're not suggesting that anyone have bariatric surgery to treat their depression," Dawes said. But, he added, it's encouraging that depression became less common post-surgery.
According to Dawes, the fact that mental health conditions were so common in this study might help lift some of the "stigma" patients can feel.
"You're not alone," he said.
Wolfe agreed. "Mental health conditions should be considered another potential comorbidity of severe obesity, just like diabetes or high blood pressure," he said.