The Zone Diet is one of the most popularized diet programs out there. The premise of the program is to eat 30% of your calories as protein, 30% as fat, and 40% as carbohydrate. This balance is distributed evenly over the course of the day, provided as 3 meals and 2 snacks. Portion control is emphasized.
In terms of the science, the Zone diet has been included in at least two clinical trials (links are here and here), neither of which showed it to be superior to the comparators (Atkins, Ornish, Weight Watchers, etc). As blogged previously, the efficacy of the diet seems to be related more to adhering to the program itself, rather than what the diet actually contains.
Is it a permanent lifestyle change? While it will always take time and attention to achieve the 30/30/40 breakdown, once you get into the rhythm of it, I think it can be continued over the long term. It’s really about whether it’s a balance that is right for you; in other words, whether this balance allows you to include the foods you enjoy, and whether you can stick to it for a lifetime.