There are 2 different groups of Diabetes Mellitus (DM): Type 1 and Type 2. Type 1 are the "insulin dependent" diabetics, as their bodies no longer make insulin (the hormone that allows the cells of your body to bring sugar from the blood stream into the cell to use for energy). These patients usually have the illness
since childhood, and there is an autoimmune etiology. What happens is the bodies immune system for some reason identifies the islet cells (insulin secreting cells) within the pancreas as foreign, and attack and destroy them. Thus the individual is dependent on exogenous (external) insulin for the rest of their life. The other (more common) class of diabetes (Type 2) is the "insulin resistant" group. In this patient population, there is so much sugar in the blood stream chronically (typically from overeating, or eating sweets, etc), and there is so much insulin being secreted all the time, that the cells to which insulin binds to allow sugar to leave the bloodstream and go into cells become desensitized to the effects of insulin. Classically this group didn't develop DM2 until the later generations of life as they became less active (so they were burning up less sugar), more sedentary, and ate more (so there was more sugar in the blood stream). Unfortunately there seems to be an epidemic of childhood obesity, and there are more and more children being diagnosed with DM2. So to answer your question, it is usually a behavior pattern of overeating that leads to the development of DM2, which of course also leads to obesity. I hope this answers your questions. If you are worried that you may be getting DM, I would recommend making an appointment with your primary care physician
to discuss your concerns. There are a few easy blood tests that they can do to help determine if you are or not. Best of luck.