The majority of obese individuals suffer from an assortment of metabolic disorders, including diabetes. However, a subset of obese people are surprisingly healthy despite being extremely overweight. In particular, some morbidly obese people are not insulin-resistant. Nuria Barbarroja led a team of scientists from Spain and Cambridge in discovering why not.
The researchers studied two groups of morbidly obese patients, one that was insulin-resistant and the other that was insulin-sensitive, like non-diabetic normal weight people. Although they had many similarities, where the groups of obese patients differed was in the expression of interleukin 1 alpha and interleukin 16, cytokines involved in immune response and in inflammation. The insulin-resistant individuals had much higher expression of both of these factors.
The researchers postulate that it is the inflammatory response that causes people to become diabetic. Most people suffer increased inflammation as they gain weight, but apparently some people don’t follow this normal pathway, and thus can remain relatively healthy, even while obese. Of course, there are other health issues associated with obesity besides diabetes, so it's still not recommended.