Carb calories may contain a higher volume, but for many they can spike the blood-sugar level, which causes a chain reaction leading to a feeling of hunger much sooner than if they'd eaten a more balanced meal. The low-carb thing works on a principle known as ketosis, which is a seperate issue. If you eat few enough carbs (which is to say, virtually none) your body will stop getting its source for glycogen, its primary & preferred fuel, which is a form of sugar - and use ketones (hence ketosis) instead. They're protein breakdown products, and they stink - being in ketosis is known to cause bad breath, among other things (weight loss being one of them - but glycogen binds to water and so when you don't have it, a lot of the weight loss is really just water loss. This is why people going on Atkins can lose 10+ pounds the first week). As for sodium, while it's true it doesn't have calories, it causes water retention. As I understand it, proper cycling of water (drinking, utilizing, urinating) is an important factor in weight loss & health, so it can have less than ideal effects.. however if you drink a lot of water, it should minimize them.