I gained weight in the 1990s when I switched from animal insulin to modern day insulins. I was not doing anything different with my eating or exercise. My routine was the same, but I kept on gaining. By the end of the 1990s I had gained 57 pounds. I was using 40% more insulin than I was using at the beginning of that decade. I was diagnosed with insulin resistance. The weight gain caused that. I was a type 1 with insulin resistance. That is called "double diabetes". My doctor prescribed a type 2 med (Avandia) to reduce the insulin resistance. It has worked well for me for 11 years now.
Several years later I joined a few online diabetes support groups. Other type 1 diabetics had the same problem and told me it was the modern day insulins that caused the weight gain. I had reduced my insulin dosage to normal and I was no longer gaining weight, but I needed to lose the weight I had already gained. I cut my daily carb intake to 130g and increased my exercising each day. In the year that followed I lost almost all the extra weight. In 2007 I started using an insulin pump. Pumping gave me much better control and I now have very few bad lows and highs. Like type 2 diabetics, I will never be able to eliminate my insulin resistance, but with Avandia and losing weight it is not giving me any problems. I have very good control after 64 years of type 1 and I have no complications.
Type 2 diabetics can also become double diabetics. For some type 2 diabetics, their is less and less insulin production as time advances. The pancreas wears down in time and they become insulin dependant. A type 2 with very little insulin production, or none at all, is a double diabetic. I have type 2 friends who use an insulin pump. They are still type 2 though since they still have the insulin resistance that made them type 2 in the first place. I am still type 1, despite my insulin resistance, since my pancreas still does not produce insulin.
Double diabetes is being diagnosed more and more often, but many doctors do not realize a type 1 can develop insulin resistance.