JAMA: Bariatric surgery decreases CV risk, but why?
“Weight loss improves diabetes and other intermediate risk factors for cardiovascular disease, suggesting that weight loss could also reduce the incidence of cardiovascular events,” Lars Sjostrom, MD, PhD, of the Institute of Medicine, Sahlgrenska University Hospital in Gothenburg, Sweden, and colleagues wrote. “However, weight loss has been paradoxically associated with an increased incidence of cardiovascular events in most epidemiological studies, even in participants who were overweight or obese at baseline.”
Because evidence is lacking as to whether weight loss can decrease cardiovascular events, Sjostrom and colleagues used the prospective, nonrandomized and ongoing Swedish Obese Subjects (SOS) study to evaluate 2,010 obese patients who underwent bariatric surgery between Sept. 1, 1987, and Jan. 31, 2001. The researchers also studied 2,037 subjects who were matched obese controls who received usual care.
The median follow-up period was 14.7 years and enrolled patients were age 37 to 60 years and had a body mass index of at least 34 in men and at least 38 in women. Of the patients who underwent surgery, 13.2 percent underwent gastric bypass, 18.7 percent underwent banding and 68.1 percent underwent vertical banded gastroplasty. The control group received usual care in the Swedish primary healthcare system.
At two, 10, 15 and 20-year follow-up, the mean change in body weight for patients in the surgery group decreased by 23 percent, 17 percent, 16 percent and 18 percent. These same figures for the control group decreased by 0 percent, 1 percent, 1 percent and 1 percent.
The authors reported that in the obese population, baseline BMI was not related to cardiovascular events during the follow-up period. Additionally, the researchers reported 49 cardiovascular deaths among the 2,037 patients in the control group compared with 28 CV deaths in the group who underwent surgery.
Overall, 234 CV events occurred among the 2,037 patients in the control group and 199 CV events occurred among the 2,010 patients in the surgery group. After the researchers performed a multivariable adjustment for baseline conditions, bariatric surgery was found to be associated with a reduced number of fatal CV deaths and a lower incidence of total CV events.
Batriatric surgery was also found to be associated with a reduced number of fatal MIs, 22 deaths in the surgery group vs. 37 deaths in the control group. An unadjusted analysis found that bariatric surgery was not related to fatal stroke incidence, but after adjustments, the researchers reported surgery to be associated with both reduced number of fatal stroke events and total stroke events.
Having a higher concentration of insulin at baseline was also linked to a more favorable outcome of bariatric surgery on CV events.
“The SOS study has shown that risk factor improvement over 10 years requires sustained and very large (10-40 kg) weight loss that typically cannot be achieved with lifestyle intervention,” the authors wrote. During the study, the researchers were unable to find an association between weight loss and reduction of CV events.
“Alternatively, following relatively modest weight loss induced by bariatric surgery, there is no further risk reduction attributable to greater, subsequent weight loss,” the researchers said. These results pinpoint the need to explore weight loss independent of bariatric surgery.
Post-hoc findings of the study showed that obese patients with higher BMIs may not benefit from bariatric surgery and that high insulin levels may be a better selection criterion for bariatric surgery compared with high BMI.
“These results—together with our previously reported associations between bariatric surgery and favorable outcomes regarding long-term changes of body weight, cardiovascular risk factors, quality of life, diabetes, cancer and mortality—demonstrate that there are many benefits to bariatric surgery and that some of these benefits are independent of the degree of the surgically induced weight loss,” the authors concluded.
“Some unidentified factor is associated with bariatric surgery operations resulting in fewer cardiovascular events and reductions in mortality that are not related to weight loss,” wrote Edward H. Livingston, MD, of the University of Texas Southwestern Medical Center in Dallas, in an accompanying editorial. Livingston speculated that patients willing to undergo bariatric surgery may be on a healthier diet or more adherent to medical treatments, which are factors not included in their BMI.
While bariatric surgery has shown to be advantageous, “the benefits from bariatric surgery operations are not related to weight loss, the main reason these operations are performed,” Livingston said.
“How, then, should physicians advise obese patients who seek bariatric surgery operations for weight loss?” Livingston asked. He offered that physicians must understand a patient's risk factor prior to sending him or her for surgery.
“In addition, given the advances in the understanding of the pathophysiological mechanisms underlying obesity, increasing evidence on the relationship between obesity and outcomes, and progress and refinements in surgical interventions for obesity, perhaps it is time for the National Institutes of Health to convene another expert panel to rigorously assess the available evidence and provide updated recommendations for bariatric procedures for the treatment of obesity,” Livingston concluded.