Low carb diets keep your glucose level from spiking, unlike a high carb diet. High levels of glucose in the blood can lead to insulin resistance, also known as Syndrome X. Syndrome X, in turn, can lead to Type 2 diabetes and Type 2 untreated leads to Type 1 diabetes.
One of the big misconceptions of dietary science is that fat consumption makes you fat. It doesn't. Carbs are high energy foods, which is why they are included in emergency rations. In emergency situations, you burn more calories, thus you need more caloric intake. If you are in a regular lifestyle or a sedentary lifestyle, the extra glucose in your system is converted via insulin into fat. That is why exercise is so important to maintaining your weight. Couple that with a low carb diet and you don't experience the spikes in glucose level that cause your body to secrete insulin, which converts that excess glucose into fat.