Studies have shown that very low calorie diets high in fat result in fat loss, whereas very low calorie diets high in carbohydrates and low in fat don't result in fat loss. A wonderful illustration of the power of our hormones. No, there are other reasons, and most relate to the general reasons why we eat too much. Obviously a big one is hunger. It's very hard not to eat when you're hungry.
Some people can do it for a little while, very few can do it all their lives.
And many of those with a serious weight problem have a genetic predisposition for an overactive appetite. Also there's boredom, just eating for something to do. Many people eat too much simply because it's pleasurable. For some the pleasure of eating provides an invaluable temporary escape from depression, anxiety, or stress. These reasons have strong psychological or genetic roots, and the Zone is not a cure for them.