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If you heard of a treatment that effectively cured 40 percent of people with a devastating common disease — cancer, say, or Alzheimer’s — that would be front-page news, right? People would be gathering around water coolers across the world to gush about the progress of medical science.

We actually do have one such success story, though most people don’t think of it in such glowing terms: weight-loss surgery. A clinical trial published in 2012 studied obese people with diabetes after receiving either intensive medical therapy (which included lifestyle coaching, home glucose monitoring, diabetes medications, and a push to join Weight Watchers) or intensive medical therapy and weight-loss surgery. About 40 percent of those who got the surgery no longer