First of all, let's see some of the philosophy behind these diets:

Carbs make your body secrete a lot of insulin. Insulin is a hormone that carries nutrients from the blood to the different parts of the body. Some insulin is good (we would die without it - diabetics need to take insulin shots for example). But too much insulin is not good because it tends to make us gain more fat (no need to analyse the biological process - just trust me, this happens).

Fat on the other hand tends to be absorbed much slower. This means that if you add fat to a food, the food will be absorbed more slowly and not that much insulin will be secreted.

So, eating more fat and less carbs helps keep your insulin levels steady throughout the day (eating 6 small meals instead of 3 big ones does the same thing). This means that you will not have so many "crashes" (like those afternoon urges for food). By the way, when you exercise (and especially when you weight train) your body becomes that much more efficient at dealing with insulin and tries to "push" the nutrients to your muscles - and not your fat reserves.

Now, in practical terms, does the "high-fat, low-carb" type of nutrition work? It depends on what we mean by "high" and "low". If you ask me, the name of the game is moderation. Do that and you should be fine. As I mentioned earlier, a typical diet, may look like this:

Carbohydrates: 60%

Protein: 10%

Fat: 30%

And I recommend something like:

Carbohydrates: 45%

Protein: 35%

Fat: 20%

So, should we take it to the extreme and do something like:

Carbohydrates: 10%

Protein: 35%

Fat: 55%

In my opinion, no. Although some people can respond well to this type of nutrition, most people won't. The main reason is that very low carb diets will tend to cannibalise your muscle tissue - because carb molecules and water molecules are stored in the muscle (again, no need to get technical - just show some blind faith here).

You lose the carbs, you lose the water - and you lose the muscle. And then you can't lose fat because your metabolism drops. Stick to the ratios I recommend (don't obsess over them - just try to approximate them) and you should be fine (more than fine actually).

Finally, let me say that an ultra low-carb diet is BRUTAL and no "normal person" will be able to stick with it and see results from. Unless they are a masochist of course. In order to succeed, you need to enjoy your program so you stick with it. This is crucial...