Considered strictly, the Zone is the optimum balance of calories from fat (30%), protein (30%) and carbohydrates (40%). It's possible to get there with a candy bar and bacon.

However, Dr. Sears and the rest of us recognize that is not an optimum diet even though it's better than letting insulin skyrocket out of control. This book on the benefits adds a new dimension to the Zone -- soy beans.

Yet, perhaps it should be said upfront, this book appears to be somewhat of an "orphan." Previous Zone books did not extol soy as a wonderful food source. That's easily explained by Dr. Sears' previous ignorance on the subject.

What may be more revealing is that subsequent Zone books also do not extol soy as a terrific food.

The problem may arise from the assertion by some alternative health experts that soy foods contain a substance called a phytoestrogen that mimics the hormone estrogen. It's not healthy for men (who need to keep estrogen lower than testosterone) and even for women to ingest substances that mimic estrogen.

Plus, there are other arguments against soy too numerous to go into here.

Dr. Sears on record that eating the amounts of soy he describes is not dangerous. Some disagree. And, to the best of my memory, none of the Zone books he wrote after this one advise readers to eat soy foods in particular. Compare this to how consistently he now writes about the benefits of fish oil.

The big argument for soy is that supposedly it's eaten by lots of Japanese -- and Japanese men have extremely low rates of prostate cancer, indicating the soy they eat is disturbing their testosterone/estrogen balance. The same argument holds for Japanese/American women and breast cancer.

Moreover, Okinawans live a lot longer than even mainstream Japanese, and eat more soy protein -- 100 grams per day on average.

Others say that the Japanese eat fermented soy products as a condiment, not as a substitute for meat.

Dr. Sears' argument in favor of eating soy is that it contains an amino acid that helps your body release more glucagon. Glucagon is the hormone which balances insulin to keep you in the Zone.

It's far easier to increase insulin through eating excess carbohydrates than it is to increase glucagon, so I can understand why he is in favor of that. But this is the only book where he advises the reader to get half of your protein calories from soy protein.

Much of this book contains recipes for Zone meals using various soy products.

If you want those recipes or you also believe that soy is a great food, then this book is a good one for you.

Personally, I just don't know what to think. I do know that I'm eating some soy protein because soy isoflavones are included as an ingredient in various Zone bars I eat. I'm not anxious to eat any more until the controversy is cleared up.