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Counting Down to Surgery

For a diabetic to qualify for gastric bypass surgery, just how high does her body mass index need to be?

Fall 2008

The body mass index, developed by the Belgian scientist Lambert Adolphe Jacques Quetelet in the 1830s, is still the gold-standard weight index for medical organizations around the world. One of its chief advantages is simplicity: Anyone with a handheld calculator—or access to any number of online calculators—can learn her BMI within seconds. The formula is weight in pounds, divided by height in inches squared, with the result multiplied by 703.

As a measure of obesity, BMI is not without flaws. For example, the index does not consider what portion of a person’s weight is muscle or fat. Because muscle weighs more, many athletes have BMIs that would classify them as overweight. Also, BMIs don’t consider waist size or body shape, which clinicians increasingly deem important health indicators.

Still, the BMI remains the determinant of candidates for gastric bypass surgery. As benefits of the surgery in helping patients with type 2 diabetes have become clear, surgeons are rethinking just how high a patient’s BMI must be to                                                                              qualify for the procedure.

Consider Sarah, who is 5 ft. 3 in. tall and has type 2 diabetes, and her options at various BMIs...


Sarah weighs 250 pounds and is seriously obese, a natural candidate for gastric bypass surgery. The twin goals of reducing weight and helping her diabetes go hand in hand.


Sarah weighs 195 pounds, still well into the obese range. Yet this is the lowest weight at which the surgery might be considered necessary both for weight loss and diabetes.


Sarah weighs 170 pounds and still needs to lose at least 30 pounds to enter the range considered healthy by the National Institutes of Health. But she is far too slender to be considered for gastric bypass for weight alone. Still, advocates of diabetes surgery think her chronic diabetes could be helped by the procedure.


At 130 pounds, Sarah is well within normal range; surgery to lose weight would be unthinkable. Yet Brazilian surgeons operated on such a patient, with a BMI of 23.4 and type 2 diabetes. The patient, like the 38 others in the study, saw dramatic improvement in what had been a chronic condition.


As surgical techniques become less invasive and the diabetes benefits even clearer, some clinicians suggest that preventive surgery may one day be viable for those of any BMI who are at especially high risk for the disease.


Bypassing Diabetes

Who needs gastric bypass surgery?

As a cure for the disease, bariatric surgery is poorly understood. But it’s so effective that it’s now being done on patients who aren’t even obese.

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