Low carb diets aim at getting your body to use fat instead of sugar as energy source. Your body has only two sources of fuel, fat or sugar. While your body can only store limited amounts of sugar, your body has plenty of fat to burn. Note that this is true even if you are not overweight.
This was explained very well in Stu Mittleman’s book Slow Burn. Mittleman was an ultradistance running champion, he ran 1000 miles in less than 12 days and 577 miles in six days. He had trained his body to use the fat instead of sugar as energy source. This made it possible for him to run such incredible distances over several days. Mittleman consumed very little carbs, this was the main way how he to turn his body into a fat burning running machine.
Nowadays, the Paleo Diet is also aiming at getting your body to rely on fat as fuel instead of sugar. Fat and protein have been the main sources of nutrients for mankind until modern society changed us. Nowadays, most people rely on carbohydrates as their main source of nutrients. One problem with this is that your body can store only a limited amount of energy as sugar, which means that you need to keep on consuming carbs in order to avoid running out of energy. Or to put in a more scientific way, a high-carb diet leads to excess production of insulin, which is needed to decrease the glucose level. This leads to fatigue and cravings for quick energy from carbohydrates.
By cutting down on carbs, you can achieve low levels of insulin, which lets you enjoy stable energy levels. This allows you to reduce excess body fat and permanently lose weight. It is especially important to limit the intake of empty calories. They contribute to your energy intake but have little other value. But you need some carbs, preferably they should come from fibrous vegetables and fruits. Such carbs cause limited rises in your blood sugar and insulin levels.
Consuming too much carbs can also lead to health issues. If your body produces too much insulin over time a number of things can go wrong. Becoming overweight is just one of the problems. Glucose that your body does not need will become saturated and the excess will be converted to fat.
So have do you start burning fat instead of sugar? The answer is easy, limit your daily intake of carbohydrates to the minimum amount needed and make sure that the carbs comes from fibrous vegetables and fruits, don’t consume sugary foods or beverages. Make sure that most of your calories come from fat and protein.