Does insulin cause weight gain?

There is no question that insulin causes weight gain. Insulin is a hormone secreted by the pancreas in response to sugar intake. Its role is to drive sugar into the cells of the body, where it is used as a source of energy (measured in calories). Insulin, therefore, pumps calories into cells. If this energy is not used by the cells or is more than is needed, it is converted into an energy storage form known as fat.

Because of these actions, insulin is called an "anabolic" hormone. The word "anabolic" means "building up tissue." If a person is using his or her muscles and is physically active, the extra energy is converted into new (larger and/or stronger) muscles rather than fat. In a sense, a person who is sedentary, not using his muscles, getting more calories than he needs, and taking insulin is in the midst of a "perfect metabolic storm" that will result in weight gain.

The issue of insulin causing weight gain has long been a troubling aspect of the treatment for type 2 diabetes. It is not a problem in type 1 diabetes, where patients have virtually no circulating insulin and need to receive it from an external source. But in type 2 diabetes, the physiology is quite different. Here the body does make insulin, but the tissues are "resistant" to its effects.

In fact, in the early stages of type 2 diabetes, insulin levels can actually be high. This occurs because the tissues are resistant to insulin, and higher insulin levels become necessary to drive sugar (glucose) into the cells and thereby drop the sugar level in the blood.

Obviously, then, using insulin to treat type 2 diabetes is problematic. Individuals with type 2 diabetes are usually overweight, and circulating insulin levels may already be high. Adding additional insulin will certainly cause weight gain - and this can actually make the insulin resistance worse. The usual justification is that using insulin will protect the remaining insulin-producing beta cells in the pancreas from having to work overtime.

Recently, this issue was reviewed by one of the leading diabetes authorities in the world, Dr. Ralph DeFronzo. In DeFronzo's prestigious Banting Lecture, which was published in the April 2009 issue of Diabetes, he suggests that the American Diabetes Association guidelines for treatment of type 2 diabetes may be misguided and in need of revision. DeFronzo argues against the use of insulin to treat type 2 diabetes.

Yes, insulin does cause weight gain. Moreover, there are several other hormones that cause weight gain in women. Estrogen, progesterone, and testosterone typically cause weight gain when production levels are low or decreased due to menopause. Cortisol (in high levels) is another hormone that causes the body to store fat and gain weight. This hormone is produced in excess during stressful situations which increases blood sugar and the unused glucose is stored as body fat.