Well actually its the opposite. There is substantial clinical evidence that there is less chance of weight gain with Levemir than with other insulins.
However, Most patients with type 2 diabetes gain weight when treated with insulin. We see this when insulin is introduced after your orals have failed, but also when the doctor puts you on insulin shortly after an initial diagnosis of diabetes.
Also, many people see weight gain at the beginning of treatment with sulfonylureas (glucotrol, amaryl, etc), even though people usually gain less weight with sulfonyulreas than with insulin. The reasons of the excess of weight gain with insulin as compared with sulfonylureas is still a mystery.
People with type 2 diabetes treated with insulin gain weight only during the first 2-3 years after insulin introduction. The weight stabilizes thereafter. However, Type 2 diabetes usually remains unknown for years before diagnosis and patients may lose weight during this long period of time before being diagnosed. Many experts think that the weight gain observed after the introduction of insulin may simply correspond to the more complete metabolization of sugars.