It’s a myth.

In order to lose fat you must lose weight and to lose weight you must eat fewer calories than you are expending. Cutting just carbohydrates is not the solution. Carbohydrates are needed so you can function properly and be able to sustain your exercise plan. Plus carbohydrates actually help you burn fat as you lose weight by transporting fat cells to be metabolized. So if you are lacking carbohydrates you may stop burning fat cells. Carbohydrates, such as whole grains, are rich in B vitamins which are key elements in helping your metabolism work, thus a diet low in whole grains negatively affects your metabolism. In addition, glucose in the blood (a simple carbohydrate) and glucose in muscle in the form of glycogen (a complex carbohydrate), are the primary sources of energy when you exercise. Therefore, if carbohydrates are either missing from your diet or are being eaten in insufficient amounts, your body will be forced to attain the glucose needed for energy from protein. Your body gets energy from protein by breaking down your muscles, which causes decreased muscle mass and can be very detrimental for the functioning of your body. Plus muscle drives your resting metabolic rate, so having a higher muscle mass helps burn more fat, even while you are at rest.