If you have type 1 diabetes, the answer is simply no. Taking insulin is a necessity because your body may not make any, or may not make enough, of the hormone.
If you have type 2 diabetes, the answer is more complicated. The first treatment your health care provider may offer is a combination of meal planning, exercise, and weight loss. Such steps can lower blood glucose. Sometimes the drop is enough to bring glucose levels down near the normal range. In that case, the lifestyle changes alone may be enough to manage your diabetes.
Over time, however, that picture may change. When type 2 diabetes first starts, your pancreas is usually making plenty of insulin, but your body has trouble using it efficiently. As time goes on, your body may stop making enough insulin. At this point, medication may be required.
Many people with type 2 diabetes eventually need medicine to properly manage their disease. Maintaining a healthy lifestyle through diet, exercise, and weight loss is still very important and should be continued, even if you are taking medications to help manage your diabetes.