I have heard that carbohydrates stimulate insulin release and insulin stores fat. Therefore, eating carbohydrates makes you fat. What is the truth?
Humans are periodic eaters but continual metabolizers. We eat more than we need at a sitting because we may have to go a period of time without food, even though the body’s energy needs are constant. This makes insulin and its storage functions necessary. Insulin takes the excess glucose to the muscle to be stored as glycogen. Insulin also takes excess glucose to the liver where it may be stored as liver glycogen, or converted to fatty acids and stored in adipose tissue. Without insulin, eating would have to be continuous, much like a hummingbird, because we would have no means of storing and retrieving energy.
This process of storing energy for later makes the serum glucose levels fall again. As a result, insulin levels drop (over approximately one hour) and glucagon is released from the pancreas. This hormone stimulates the release of glycogen and fatty acids into the blood. Thus, the energy that was stored is later retrieved. The net amount of fat in storage at the end of the day is dependent only on how many calories were eaten versus how many were burned. Proponents of this misconception are often those who believe in eating a high protein diet in an effort to either gain muscle or avoid/lose fat. The irony is that protein stimulates insulin secretion too (it just so happens that insulin is involved in protein synthesis, which requires amino acids to occur). Oddly, this fact is never mentioned by the anti-carbohydrate, high–protein hordes.