What the developer aimed while introducing the zone diet was the increase in the protein and fat consumption and reduction in that of carbohydrates. The funda that was cited dates back to evolution of species. He propounded the theory that homo sapiens (humans) were essentially meat eaters. Our ancestors' diets were mainly of meat, fruits and vegetables. Thus, our diets should be the same.
The imbalance in our systems are a result of modifications on that basic diet viz inclusion of more carbohydrates, less proteins and fat.
The zone diet is also called the 40-30-30 plan, since the proportion of carbohydrates, proteins and fat has to be in that ration. The formula is controversial, but studies over the past several years (including non-scientific study by Scientific American Frontiers) have shown it to produce rapid weight loss.