The Internet is abuzz with discussion of a recent study that showed that overweight people with type 2 diabetes lived longer than those who were normal weight.

Most of the news services as well as the New York Times recently had stories about the study.

The researchers had several theories for the effect.

First, doctors may treat normal-weight patients less aggressively than overweight patients, not pushing them as hard to modify their diets and get more exercise. And the patients themselves might not be as careful with their diet and exercise because they “may have a false sense of protection because they are not overweight or obese,” as stated in an editorial accompanying the article.

Second, many doctors don’t suspect type 2 diabetes in people who aren’t overweight, so the normal-weight patients might be diagnosed at later stages of the disease when it’s harder to control. One patient wrote that he suspected he had diabetes and begged his doctor for testing but the doctor just laughed at him because he wasn’t overweight.

Another factor, which I pointed out in the comments section of the Times article, is that the “type 2 patients” being studied might not all have been type 2 after all. Most of us know there are types of diabetes that aren’t type 1 or type 2, which is defined by having insulin resistance. They include LADA (latent autoimmune diabetes of adults), a slower moving form of type 1 diabetes found in older patients; MODY (maturity-onset diabetes of the young), a monogenic disease (meaning it’s caused by a mutation in just one gene, whereas type 2 is polygenic) that often appears in young people but sometimes is first found when they’re older; and “Flatbush diabetes,” also called ketosis-prone diabetes or diabetes type 1b, primarily found in people of sub-Saharan African descent but also sometimes found in other ethnic groups. There are other rarer types of diabetes and there may be types too that simply haven’t been discovered yet.

If someone has LADA and is treated with oral drugs for several years and the oral drugs don’t work, it means they’ve spent several more years with higher blood glucose levels than someone with real type 2, in which the orals usually help. I know someone whose A1c’s kept going up and up, and she begged to go on insulin, but the nurse practitioner she was assigned to kept telling her she was producing plenty of insulin but her body just wasn’t able to use it. She finally got to see an endocrinologist, who diagnosed type 1 and put her on insulin, and her A1c’s came down.

So too, so few medical people are familiar with MODY and Flatbush diabetes that they may not know the best way to treat them.

As I noted in the Times comments, being overweight may also trigger type 2 at a younger age, so you seem to live longer after diagnosis, just as early detection of an incurable form of cancer sometimes seems to show that people live longer with early detection even though they die at the same age as someone diagnosed at a later stage. There’s just a longer time between diagnosis and death.