Organ dysfunction identified at-risk bariatric candidates

Clinical takeaway: BMI may establish candidacy, but documented organ dysfunction is what distinguishes a patient being treated for active disease from one being treated to prevent it. That distinction can matter for how referrals are framed and how risk is discussed pre-op.

BMI was built to sort populations, not to describe the patient in front of you. It takes two measurements and returns a ratio, and that ratio carries no information about whether a patient's knees, liver, kidneys, or airway have already started to fail. Elsewhere in medicine, a diagnosis names damage. Obesity has been the exception, defined by body size with the rest implied.

But that gap now has formal criteria attached. A Lancet Diabetes and Endocrinology commission separated clinical obesity, where excess adiposity is already producing organ dysfunction or functional limitation, from preclinical obesity, where function is preserved. The stakes sit with the referral: BMI thresholds and a short list of qualifying conditions still determine who reaches a bariatric program and how urgently, so candidates get sorted by size while the disease that justifies the operation may go unmeasured.

Clinical obesity accounted for 1,709 of 2,316 bariatric patients, or 73.8%, and was the leading category at every site, from 62.7% to 79.3%. That left roughly one in four candidates with no documented adiposity-related organ dysfunction. Within each cohort, mean BMI in the two groups was statistically indistinguishable.

What did separate the groups was time and accumulated damage. Patients with clinical obesity were seven to 11 years older and scored higher on the American Society of Anesthesiologists (ASA) physical status classification in all four cohorts. The qualifying dysfunctions within the clinical obesity group were hypertension in 57.6%, metabolic dysfunction in 44.1%, sleep apnea requiring CPAP in 40.1%, and functional or musculoskeletal limitation in 20.1%.

Estimated long-term risk ran the same direction, with higher Charlson Comorbidity Index and Framingham coronary risk scores in every cohort where the measure was available. Observed harm offered a less consistent case. Major 30-day complications were higher in clinical obesity at one center, 4.0% versus 1.1%, with no separation at the two others where complication data existed.

The four centers were high-volume tertiary programs in the UK, Spain, France, and Brazil, with no US site. Investigators applied the commission criteria retrospectively to adults who underwent primary laparoscopic gastric bypass or sleeve gastrectomy between 2014 and 2025, adjudicating 18 organ dysfunction domains from existing chart data: diagnoses, labs, imaging, medication use, specialist follow-up, and documented functional limitation.

Preclinical obesity is not a weaker indication; those patients lost at least as much weight after surgery. What changes is the purpose of the operation, and therefore what counts as success. Treating established disease means watching organ function, medication burden, and events. Preventing it means watching whether disease arrives at all, on a horizon measured in years.

Senior author on this analysis, Francesco Rubino of King's College London, chaired the Lancet commission that produced the definition of clinical obesity applied here.

"Reliance on BMI thresholds and the traditional framing of MBS (metabolic bariatric surgery) as weight loss surgery have reinforced its indication as a preventive intervention rather than treatment for active disease, potentially contributing to persistent underuse despite strong evidence of efficacy, safety, and cost-effectiveness," the authors conclude.

Source: Cremona S, et al. (2026 Aug 11) JAMA Netw Open. New Obesity Definition and Clinical Obesity Prevalence for Global Metabolic Bariatric Surgery