As you now know, the Atkins plan begins by restricting carbohydrates. When your body is not given fuel in the form of carbohydrates, it uses fuel in other ways. So, let's say you've just started following the Atkins plan and are consuming a modest 20 grams of carbohydrates or less. Here is what's happening inside your body:
The liver stores glucose by converting it to glycogen. It holds perhaps a 12-hour supply of glucose in its glycogen. Once you finish digesting all of the carbohydrates that you last ate, the liver starts converting its stored glycogen back into glucose and releases it to maintain glucose in the blood. Lipolysis also starts breaking down fat in the fat cells and releasing fatty acids into the bloodstream. Tissues that do not need to use glucose for energy (for example, muscle cells) start burning the fatty acids. This reduces the glucose demand so that nerve cells get the glucose. Once the liver runs out of glycogen, the liver converts to a process called gluconeogenesis. Gluconeogenesis turns amino acids into glucose. The liver then begins producing ketone bodies from fatty acids being made available in the blood by lipolysis. Brain and nerve cells convert over from being pure consumers of glucose to partial consumers of ketone bodies for energy. This process is called ketosis -- which is why the Atkins plan is also known as a ketogenic diet.
So, what does this mean in simple terms? In theory, the Atkins diet enables your body to switch from a machine that uses carbohydrates for fuel to one that uses fat for fuel. Therefore, a diet with little or no carbs forces the body's storage of fat to become its main energy source.
To further understand the way your body loses weight on the Atkins diet, you must consider the way the body uses sugar as fuel. To turn sugars into fuel, your body uses the hormone insulin. Insulin enables our cells to turn carbohydrates into glucose by controlling the amount of sugar in our blood. The body secretes insulin to keep blood sugar from getting too high. Insulin is a storage hormone, meaning that it causes sugar we don't use for fuel to be stored as fat. It also keeps the body from burning stored fat. The Atkins diet suggests that it is this "insulin response" that continues to add fat to our bodies. This function is an asset when food is scarce, but an abundance of sugar-filled and high-carbohydrate foods will promote the accumulation of body fat.
On the contrary, a low-carbohydrate diet allows your body to release less insulin. According to the Atkins plan, when insulin levels are normal, your body will begin to burn its own fat as fuel; thereby resulting in weight loss. By keeping insulin levels stable, not only does your body burn fat, but it may also lead to less hunger and fewer cravings. Simply put, according to the Atkins folks, their diet attempts to control insulin levels by controlling the amount of carbohydrates you eat.