Many published studies on bariatric surgery are retrospective, short-term analyses with insufficient follow-up. “Obesity is a chronic illness that is linked to important comorbidities,” says Nancy Puzziferri, MD, MS. “Obesity treatments need to be assessed in long-term studies, particularly for invasive procedures like bariatric surgery.”

There is plenty of short-term evidence about the benefits and risks of bariatric surgery for up to 1 year after the procedure, but few data are available about long-term outcomes. Some short-term reports may reach optimistic conclusions regarding the effect of bariatric surgery because follow-up is incomplete. This can lead to over-estimating the beneficial effects of these operations.

A Systematic Review of Bariatric Surgery

In a systematic review published in JAMA, Dr. Puzziferri and colleagues sought to determine the association of bariatric surgery with outcomes of weight loss, diabetes, hypertension, and hyperlipidemia. The analysis involved studies that lasted at least 2 years in duration and with at least 80% follow-up of patients. Of the more than 7,000 clinical studies reviewed in the analysis, less than 1% met inclusion criteria.


Studies of the long-term outcomes of bariatric surgery demonstrated substantial and sustained weight loss for gastric bypass procedures that exceed outcomes from gastric banding. “Despite the increasing popularity of gastric sleeve operations, there were few long-term studies with reliable follow-up for these procedures,” says Dr. Puzziferri. The review in JAMA also found that just 16% of the studies reviewed reported outcomes at more than 2 years after bariatric surgery, and less than 3% reported weight loss outcomes for more than 80% of the original cohort.

In addition, few studies measured comorbidity improvement after the completion of bariatric surgery. For type 2 diabetes, remission rates were 66.7% for gastric bypass surgery and 28.6% for gastric banding procedures. For hypertension, remission rates were 38.2% for gastric bypass and 17.4% for gastric banding. For hyperlipidemia, remission rates were 60.4% and 22.7% for gastric bypass and for gastric banding, respectively. Improvements in these obesity-related comorbidities were mostly reported as secondary outcomes.

More Research Needed on Long-Term Outcomes

To reliably assess how bariatric surgery performs over time, Dr. Puzziferri says that researchers should follow up the majority of patients in studies for longer durations. “Ideally,” she says, “long-term outcomes studies should report results for at least 80% of initial cohorts and with follow-up going beyond 2 years so that we can fully characterize the efficacy of bariatric surgery.” She notes that study designers should work toward developing and adopting protocols for handling missing data and dropouts in the future.