I think that depends on how you define diet selkirk.
Fundamentally a diet is the food and drink regularly consumed... basically we are all on a diet. Each of our diets is different as we consume different percentages of carbs, protein and fats on a daily basis.
The zone diet encourages a ratio of these three and then depending on your fitness/health goals allows you to scale it up or down depending on if you want to lose or gain weight.
The zone diet is more an approach to daily nutrition and healthy living and not a quick fix for body weight (though it turns out most people lose weight on it).