Well even on Atkins, when you reach pre-maintenance and maintenance, you will be upping your carbs. Eat a piece of cake and the results will be the same, whether your on the Zone or Atkins diet. Basically, the Zone is Atkins at pre-maintenance, only more specific in the amount of protein, carbs and fat you eat and they are eaten together at each meal and snack.

I am not sure that is absolutely correct (the part about gaining the same weight on the Zone or Atkins).

Here is why. My science is a bit rusty, but I believe the math is that every glucose molecule in your system is attached to 3 water molecules. So, when you go from <20g of carbs per day (constantly being burned, no time for storage) to enough carbs to fill up your liver with glycogen (strings of glucose molecules), you will add lots of water. Many Atkins dieters assume that they just gained three pounds. You cannot take 4 oz of food and gain 3 pounds of fat from it. You can however gain 3 pounds of water. This is also why everyone on Atkins loses 4-7lbs in 48 hours. Anyone on this board can tell you that fat can come off very quickly, but not that quickly. At that rate, we could all lose 15lbs per week, 60 lbs per month and a 275 lb person could weight 120 in 10 weeks.

Anyways, on the Zone, if you are eating 40% carbs in a 1500 calorie diet, that is 600 calories per day, and that leads to 150 grams of carbs which keeps your water levels pretty even. A piece of cake will probably not do much to your weight if you compensate somewhere else with less carbs. However, you should always try to mix protein and fat with your carbs to slow your insulin release. Cake by itself could drive you into a binge if you are not careful. For most low carbers, sugar and flour together is very dangerous.

Also, I don't think that Atkins will ever become the Zone even at Lifetime Maintenance because he seems to think that very few of his followers will ever get up past 80-90g of carbs per day (unless they do vigorous exercise 5 days per week for at least 45 minutes). The Zone will have just about anyone getting almost half of their calories from carbs (200 g per day on a 2000 calorie diet) which is a heck of alot more that Atkins.