The Zone Diet is being promoted as healthful in 2 books by Barry Sears. I have read both of them, and he has made some interesting observations regarding carbohydrates, insulin and weight gain. His diet, in my opinion, has some excellent components and some disturbing ones. However that does not mean they should give up eating carbohydrates.
Carbohydrates are the main source of fuel for our brains and muscles.
Without them, it is difficult to think clearly, or have strength or stamina. Not all carbohydrates are created equally. For example, a bowl of Special K and a bowl of oatmeal, both good sources of carbohydrates, have very different levels of fiber, especially water soluble fiber, which slows down the rate of digestion and absorption into the blood stream. The rate at which glucose enters the blood stream will affect the secretion of insulin. Carbohydrates tend to empty from the digestive system quickly if consumed alone.