Originally Answered: Atkins diet?
Check out lowcarber.org, which has lots of information about various low carb diets.
The basic principle is that sugars and carbohydrates, which are chains of simple sugars cause changes in your body chemistry. When you eat those things your body produces insulin to help process them, but then the insulin is still floating around in your system. You get cravings for more carbohydrates to even out your insulin level. This causes overeating and insulin resistance.
If you cut down on the carbohydrates that don't provide much nutrition anyway, like white bread, pasta, potatoes, and sugar rich food, your body will not be burning those foods up for energy - or storing the excess as fat. Instead, your body will begin to burn its own fat.
So if you reduce your carbs you'll have less of the insulin resistance that causes overeating (and in my case, lethargy) and your body will begin burning fat.
It's important to do this the right way. It's not just eating tons of meat. I did the diet without increasing my meat intake at all. I just substituted healthy vegetables for starches. I never felt hungry because on that diet you can have cheese and salad dressing and butter - all the extras that give food flavor. The fat helps you to fill more full, so you don't feel starved.
It's a very hard diet to do if you have a craving for sweets.