The Zone Diet is built upon the concepts of balance and moderation.  It was created by Barry Sears, a former biotechnology researcher at the Massachusetts Institute of Technology. 

The zone talked about by Sears refers to the physiological state in which the hormones affected by the food you consume are kept within zones that are neither too high nor too low.  These hormones are known as insulin and eicosanoids and can benefit greatly from being controlled. 

By maintaining insulin levels, you can increase fat loss, reduce your risk of cardiovascular disease, and improve both your physical and mental performance.  Likewise, by controlling eicosanoids, you can reduce inflammation, increase blood flow, and improve any chronic disease conditions that you might be suffering from.   

In the Zone Diet, then, you will be consistently controlling your insulin by balancing protein and carbohydrates at every meal.  You will be consuming a moderate level of carbohydrates, moderate protein, and moderate fats.  You should eat no more low-fat protein at each meal than a serving the size of the palm of your hand.   Most of your carbohydrates should come from vegetables and fruits, with starches such as bread, potatoes, rice, and pasta used as condiments.  The majority of the fat you consume should be monounsaturated fat. 

The ultimate goal of the Zone Diet is to maintain a hormonal balance between fat-storing insulin and the hormone glucagons, which is responsible for releasing stored glucose from the liver whenever it is needed.  In essence, the Zone is a hormonal control strategy you can follow your entire life. 

Under the Zone, you will eat a combination of low-fat protein, fats, and carbohydrates in the form of fiber-rich fruits and vegetables.  You’ll have to eat proteins with each meal and snack.  You should also consume twice as many carbohydrates as protein—this can mean eating anything from vegetables and beans to whole grains.  You should eat only small amounts of unfavorable carbohydrates such as brown rice, pasta, bananas, and bagels.  
The Zone operates under the principle that dietary fat alone does not make you fat.  Rather, it is based on the idea that an excessive amount of insulin can cause you to become fat and can thwart your efforts to lose weight. 

While followers of the Zone hail it as a breakthrough for weight loss, critics contend that much of that weight loss is the result of dehydration.  Also, the Zone can lead to a state known as ketosis, which can, in turn, lead to anorexia as well as dangerous feelings of euphoria.   The diet plan could also give rise to inadequate calcium consumption, which can lead to osteoporosis.  An individual’s fiber consumption level could also become dangerously low under the Zone strategy for weight loss.  

One of the positive aspects of the Zone is that it encourages you to eat throughout the day, which can keep your metabolism rate humming.  It eliminates junk food from your diet, and encourages you to eat healthy foods instead.  Still, critics contend that the short-term weight loss offered by the Zone is not worth the potential long-term health risks.