While the immediate goal of bariatric surgery is to help obese patients shed significant weight, new research shows it may also reduce diabetes complications, including nerve damage.
Investigators followed 127 weight-loss surgery patients for two years. They found the surgery led to a sustained drop in previously high blood sugar (glucose) levels as well as in levels of certain lipids (fats).
But the procedure was also linked to marked improvements of peripheral neuropathy, a condition that undermines nerve fiber density throughout the body. It can cause weakness, numbness and pain, often in the hands and feet.
"We were not surprised to see that patient's neuropathy improved, because bariatric surgery improves obesity, diabetes, and cholesterol," explained study author Dr. Brian Callaghan, a neurologist at University of Michigan Health.
A strict diet alone -- absent surgery -- can also foster the kind of metabolic improvements that lower diabetes risk, Callaghan acknowledged. Diet alone can also lead to some neurological improvement, he noted.
But he stressed that his team found that "the metabolic and neuropathy improvements were both more impressive after bariatric surgery."
More than 100 million Americans are obese, the study authors pointed out. They also noted that obesity is the second leading risk factor for developing peripheral neuropathy, which affects in excess of 30 million Americans.
Callaghan said bariatric surgery is typically reserved for patients who "have tried to lose weight and have been unable to, especially those that have a very high body mass index [BMI]," a standard measure for obesity.
Study patients were 18 years old and up, with a BMI of 35 or more. Anyone with a BMI of 30 or higher is classified as obese. All underwent bariatric surgery at some point between 2015 and 2018.
To assess peripheral neuropathy status, skin biopsies were performed prior to surgery to measure nerve fiber density in the thigh and leg. Blood analyses were also conducted to gauge pre-operation blood sugar and lipid levels.
In addition, two years after surgery a little more than 60% of the patients underwent in-person follow-up testing, alongside roughly 20% who engaged in virtual follow-ups due to the onset of the COVID-19 pandemic.
On average, patients had lost more than 66 pounds (30 kg). The team found that nearly all metabolic risk factors --including blood sugar and blood lipid levels -- had "significantly improved," though no improvement was seen in terms of blood pressure or total cholesterol levels.
Improved metabolic profiles appeared to have a positive impact on both pre-diabetes and diabetes risk, with improvements seen among 54% of the patients and stabilization seen among roughly 44% of patients.
In terms of peripheral neuropathy, investigators found that surgery triggered improvements in nerve fiber density across the thigh, suggesting the intervention had encouraged damaged nerves to regenerate. Nerve fiber density in the leg was found to have stabilized.
Weight-loss surgery patients also experienced a significant drop in pain associated with prior nerve damage. In addition, they reported significant improvements in overall quality of life and quality of life related to neurological foot problems.
Callaghan said more research is needed to better understand precisely how weight-loss surgery triggers such neurological benefits.
"We think that weight loss is a major factor, especially since diet also seems to improve peripheral neuropathy, but it is also possible that surgical changes play a role that do not lead to weight loss," he said.
"This remains a very important thing to study going forward," Callaghan added. He noted that his team has already embarked on another investigation that will explore whether exercise, bariatric surgery or both help peripheral neuropathy the most.
Dr. John Morton is division chief of bariatric and minimally invasive surgery with the Yale School of Medicine.
Morton said it's not easy to assess the kinds of neurological changes the team observed -- because nerve regrowth tends to unfold very slowly. However, he, too, said he was "not surprised" by the findings.
"Surgery is unique," Morton said, in terms of its impact on hormones linked to weight loss and hunger and its impact on metabolism and brain-gut interactions. So when it comes to tackling diabetes risk factors and peripheral neuropathy, bariatric surgery appears to offer "many pathways to success," relative to diet alone.
His take: "Consider bariatric surgery strongly if you have diabetes and obesity. They can not only be managed, but put into remission."
Morton, who was not involved in this study, also chairs the American College of Surgeons' Committee for Metabolic and Bariatric Surgery.
The study findings were published recently in the journal Diabetologia.