Registry of 1.26 million bariatric patients finds higher risk above BMI 70, with absolute rates still low

A study of nearly 1.8 million operations in the main United States bariatric surgery registry has put numbers to a group surgeons see regularly but that research has largely skipped: people whose body mass index is 60 or higher.

Body mass index, or BMI, is weight divided by height squared. It is a blunt measure and says little about any one person's health, but it is the number most surgical programs use to sort risk. A BMI of 60 is roughly a person of average height carrying about 350 pounds.

The analysis drew on the Metabolic and Bariatric Surgery Accreditation and Quality Improvement Program, known as MBSAQIP, which collects standardized data from accredited surgical centers. Researchers examined cases from 2015 through 2023 and compared six BMI bands, from under 40 up through 80 and above.

Extreme obesity was 5.3% of the eligible surgical sample

Across 1,795,127 cases covering 1,262,454 patients, 5.3% met the study's definition of extreme obesity, a BMI of 60 or above. Patients at BMI 70 or higher were a smaller but steady presence, about 1.1% of cases every year, which came to 13,677 cases over the nine years.

That steadiness matters. It means the highest-BMI patients are not a rare event that a program encounters once. They are a small, consistent share of the operating schedule at accredited centers nationwide.

These patients arrived sicker. Compared with patients below BMI 40, those at BMI 70 or above more often had high blood pressure, 56.7% against 46.9%, and sleep apnea, 59.6% against 34.6%. Chronic obstructive pulmonary disease, a long-term lung condition, was present in 2.6% against 1.1%. Functional dependence, meaning a person needed help with daily activities such as dressing or bathing, was recorded in 4.5% against 0.5%.

Complications and deaths rose with BMI but stayed under 3%

Serious complications within 30 days of surgery occurred in 2.6% of patients at BMI 70 or higher, compared with 0.7% of patients below BMI 40. Deaths within 30 days were 0.35% against 0.05%. Both differences were statistically significant, meaning they are unlikely to be chance.

Read as a ratio, the risk looks steep. Read as a count, it looks different. At BMI 70 and above, roughly 97 of every 100 patients had no serious complication in the first month, and roughly 996 of every 1,000 were alive at 30 days.

The authors make that point directly. Their stated conclusion is that although greater BMI is associated with a progressively higher burden of illness and more complications, absolute events are low and do not contraindicate multidisciplinary obesity treatment. They also write that strategies to reduce BMI before surgery in the heaviest patients warrant evaluation, which is a call for more research rather than a recommendation any patient should act on alone.

A 30-day snapshot, not a long-term outcome study

This is a cross-sectional analysis of registry data. It describes who had surgery and what happened in the first 30 days. It does not report weight loss, diabetes remission, quality of life, or survival beyond one month, and it cannot say whether surgery left these patients better off than not having surgery.

Registry data also reflects who was selected for an operation. Surgeons at accredited centers decide which patients to schedule, and the healthiest candidates within any BMI band are the likeliest to reach the operating room. That selection almost certainly makes the reported complication rates lower than they would be if every person at these BMIs had surgery.

Finally, MBSAQIP covers accredited centers. Results from non-accredited settings are not captured here and may differ.