1. Emphasis on More protein, Fewer Carbs Worries Nutritionists
Author Barry Sears, Ph.D. developed the Zone Diet as a means to manage body weight, heart disease of controlling the body's production of insulin. His formula is to ingest calories in the following proportions of macronutrients: 30 percent protein, 30 percent fat and 40 percent carbohydrates. For most people, this means shifting consumption away from carbohydrates over to protein. Nutritionists worry that this takes away from beneficial nutrients and fibers such as those found in fruits, vegetables and whole grains, while increasing consumption of saturated fats found in animal proteins.
2. Claims and Expectation Overreach, Without Validation
Unfortunately, much of the weight loss and health benefit claims for the Zone Diet are theoretical, not validated in scientifically controlled studies. Plenty of testimonials are provided by the book, and some independent research has shown that adherence to The Zone produces positive weight loss and health benefits. But virtually all diets that effect better eating habits are effective to some degree, say critics.
3. Some Nutritionists Give it Cautionary Approval
Despite a lack of clinical research data, leading nutrition experts see benefits in the Zone Diet. For example, Bonnie Leibman, MS and nutrition director for the venerable Center for Science in the Public Interest (CSPI) says, "If you ignore the scientific rhetoric, the diet isn't bad."
Susan Roberts, a Ph.D. at Tufts University's Weight Regulation Program, says the Zone Diet's approach to blood glucose (sugar) levels has merit, but fails to account for the importance of fiber and caloric density.
4. Recommendations may be out of Date
Since the book was written in the 1990s, consumers and products made for them have evolved to better choices. Instead of referring to fats as a single, broad entity, we now know to distinguish between good (unsaturated, from plants and fish) and bad (saturated, from beef, chicken, pork and dairy) fats. Carbohydrate products made with whole grains--breads, pastas, even pizza crusts--present an entirely different nutritional profile than the refined flour versions popularized in the 20th century. The effect of these newer products on blood sugar is less troublesome.
5. May Work for Some
The nature of dieting suggests a short-term effort, something one does to achieve a weight loss goal. Getting "into the Zone" for many represents just such a task. And what works for one may not work for another. Robert H. Eckel, MD, from the University of Colorado/Denver speaks to the unknowns of dieting and obesity: "The right diet needs to be matched with the right patient. Physicians and other health care professions should teach obese patients that both quality and quantity of the diet are important." He further emphasizes the importance of exercise and a "low fad" approach to continued caloric restriction.
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