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The zone diet plan addresses the problem of the majority of diets. Namely, that in the body, excess carbohydrates are turned into fat once the limited glycogen stores are full. (excess protein and excess fat are also turned into fat). When high levels of carbohydrates are consumed at once, blood glucose levels rise. The hormone insulin is then excreted to ensure the glucose is transferred from the blood to the cells. Because insulin is basically a storage hormone, not only does that mean that the excess carbohydrates are stored as fat, but the fat you already have in your fat-storing (adiose) cells will not be released. So you don't burn fat while you are secreting insulin.

So your diet shouldn't be too high in carbohydrates (think the Pritikin diet - which will not give you enough of the good fats your body needs, either). But then, neither should your diet be so low in carbs that it induces ketosis as a prolonged dietary experience (think atkins diet). That stresses the body - it causes a buildup of acids in the bloodstream.

The body's response to excess dietary acidity is to buffer the acids with blood bicarbonate. This only works for a little while, however. What happens next is the body's renal system kicks in - which means you will urinate a lot. Unless you have kidney problems, there's nothing wrong with that per se - however what it does mean is that the weight you are losing is mostly water. Not fat. You will dehydrate yourself, as well as ending up with metabolic alkalosis. Not to mention possible neural and mental effects.

The zone perfect diet uses the dietary principles 40,30,30 as a guide to preparing each zone diet meal or snack: 40% carbohydrates, 30% fat, 30% protein. The exact amount is different for each person depending on your activity levels etc. Each person will consume a different number of "blocks" per meal. 1 block of protein is 7g, 1 block of carb 9g, 1 block of fat is 1.5g. You will always consume equal numbers of blocks in a meal or snack (ie. 3 blocks carb, 3 blocks fat, 3 blocks of protein). But the amount of each nutrient won't be the same as the grams per block are different.

In the above example, you would have consumed 33g carbohydrates, 21g protein, and 4.5g fat. It is important to calculate how many blocks you should be consuming in each meal. You can do that by refering to the books or consulting with a zone nutritionist.