The Zone Diet gets its fair share of jokes about its name, but it basically comes down to being a diet that take hormone balance as its starting point. The zone of The Zone Diet is an actual physiological state rather than some sort of state of mind; a state in the body's insulin is controlled with the eventual payoff being loss of fat and a general higher state of well being.
How is this zone achieved? How does one actually control a physiological occurrence such as the production of insulin? According to the creators of The Zone Diet, this is accomplished through balance. No, not balancing of the light and dark sides of the Force, but rather balancing one's ingestion of protein and carbohydrates.
Just as in Zen Buddhism, achieving the zone known as Enlightenment requires moderation in all things, so is moderation the goal of the Zone Diet. The diet tries for a moderate balance of consumption of protein, fat and carbs. There is even a ratio to define how much of each of these types of food should be consumed: 40% of your food intake should be carbs with the other 60% divided equally among fat and protein.
The Zone Diet is one of the big three new diet plans that considers carbohydrate control to be the key to weight loss rather than controlling one's ingestion of fat. Like the Atkins Diet and the South Beach Diet, the primary goal of the Zone Diet is to limit carbs from your diet. The criticism of the diet is similar to that of those two diets; that weight loss will be temporary and, worse, increase cholesterol and the risks of developing heart disease. The American Heart Association has been one of the most vocal critics of the Zone Diet.
Another criticism of the Zone Diet is that it requires far more effort than most others. In order to meet the ratio of the zone, you have to carefully measure every individual serving of food you eat. Many people simply don't have the time required to dedicate themselves to this aspect and winding up consulting a dietician which, while saving time, costs money.
On the other hand, if you enjoy your daily dose of carbohydrates and aren't in a big hurry to sacrifice them for the payoff of weight loss, the Zone Diet is probably a better choice for you than the Atkins or South Beach diets. With the Zone Diet you can actually consume more carbs per day than with those other two.
What this means is that those people who tend to give up on diets due to the psychological effects of feeling as if they are being unfairly deprived of the food they crave may be more successful with the Zone because it isn't quite as restrictive.
Needless to say, before embarking on the Zone Diet or any diet, it is wise to consult a doctor first.