During the week (Monday - Friday), you eat (by calories) about 55..60% fat, 30..35% protein, and no more than 30g of carbohydrates.

The plentiful supply of fat causes a metabolic shift from primarily burning carbs to primarily burning fats. Insulin levels remains low (which increases GH release). Increased dietary fat is also linked to increased testosterone levels.

Despite popular belief, the human body can run pretty well without carbs (otherwise Eskimos wouldn't be doing too well). During the weekend (Saturday - Sunday, about 24 to 48 hours), you eat a high carb, medium fat (30..40%), low protein (10..15%) diet. This causes an insulin spike. While this can increase fat deposits, it moves more nutrients into your muscles, and has an anabolic effect. The important thing is to switch back to the high fat / low carb mode before you put on too much fat.

What are the benefits ?

Increased lean body mass without the use of illegal substances.

Maximize the effects of your own hormones.

Reduced cortisol levels resulting in reduced catabolism.

Increased energy level compared to low-fat diets.

Decrease body fat without increasing lean mass, e.g. lose 90% fat, 10% muscle instead of 60% fat
40% muscle on most other diets.

Burning fat is less efficient -> increased metabolic rate.

Plentiful supply of protein.

What about Cholesterol ?

If you keep your fat intake somewhat balanced, i.e. not exclusively saturated fats, you should have no problem. For example, eggs tend to increase your HDL level (good Cholesterol). Your actual mileage may vary - test your Cholesterol level before you start.

Getting started / tips

Eat 5 to 6 meals daily.

Eat something when you are hungry - don't wait.

Keep sodium intake reasonable, some meat products can be pretty high.

Drink enough water !

This diet doesn't work if your fat intake goes too low (below about 40%).

Start at around 3000 calories per day (or 18*bw), then adjust up or down depending on your results and goals.

You may need to use a fiber supplement (watch out for hidden carbs).

First week can be rough - stick with it.

Regularly check bodyfat percentage (for example using calipers).

During the weekend, be careful with foods with high glycemic index - they can wreak havoc on your insulin level, and switch you into fat storage mode more quickly.

Low carb foods

Try to get as much natural fiber as possible from salad or vegetables, while staying within the 30g carb target.

The usual suspects:
Beef, Chicken etc. Fish Cheese Butter Any kind of oil

Almonds (1oz = 5..6g), Asparagus, Avocado (1/2 = 6g), Broccoli, Cauliflower, Eggplant, Green beans, Lettuce, Mushrooms, Olives, Peanuts (1oz = 6g), Red / Green peppers, Spinach, Sprouts, Tofu, soy milk, Zucchini

Caesar salad dressing, Oil and vinegar salad dressing, Mustard (e.g. Dijon), Pickles, Sour cream

For the sweet tooth:
Dole or Welsh no sugar added fruit pops (6g each) Sugar free Jell-O + whipped cream (within reason) Caffeine can help burn fat (but only on a low carb / high fat diet).
Ephedrine is questionable.