A low-carbohydrate diet is any kind of diet that restricts calories to below the level of national recommendations. These diets are built on the premise that humans never evolved to consume such a wide variety of synthesized carbohydrates, which became a main source of food at the time of the agricultural revolution. The science behind carbohydrates is constantly changing to reveal new insights into the way in which this nutrient affects us.
Restricting carbohydrates does not mean cutting out carbs from your diet altogether. In fact, carbs impart beneficial nutrients and play an important role in the production of usable energy molecules. But mounting evidence suggests that the human body can't deal with certain carbs. Fructose in particular is metabolized by the liver, where it becomes fat.
Some carbs cause rapid spikes in blood glucose levels, which forces insulin to store the extra glucose as fat. Physician Solomon Berson and Nobel Prize winner Rosalyn Yelow once called insulin "the principal regulator of fat metabolism." There is some controversy about the role that insulin actually plays in fat loss. Some stick to the calories in/calories out orthodoxy, but many physicians are beginning to see insulin as the key factor to weight gain and loss.
Most foods that elicit an insulin response typically contain refined carbs, fructose and other types of sugar. The Glycemic Index is the name given to a scale that measures the effect that carbs have on blood sugar. High GI foods such as potatoes and maltose have a GI of 70 and above. Low GI is 55 and below.
One 2008 study in the American Journal of Physiology found that chronic fructose consumption causes a leptin resistance. Leptin is an important hormone that regulates hunger and metabolism. A leptin resistance may cause an individual to eat more food without feeling satiated and gain weight in response. It is well established that low GI foods reduce hunger and keep you feeling full.
The argument is that a low-carb diet will naturally satiate hunger, negating the need to carefully count calories, and stimulate the use of stored fat tissue as a form of energy. If you are going to embark on a low-carb diet, it is important that you become stingy about the type of carbs you ultimately eat. In combination with moderate calorie intake, many people have found success restricting carbs.