The Zone Diet Phenomenon: A Closer Look at the Science behind the Claims

Abstract

The purported health benefits of low-carbohydrate diets have been advocated intermittently over the last century and have enjoyed increasing popularity over the last decade. Although most revolve around the emphatic theme that carbohydrates are to blame for many chronic diseases, their specific ideologies are more variable and in some cases quite sophisticated. The Zone Diet phenomenon represents a new generation of modern low carbohydrate food fad with sales placing it among the most popular diet books in recent history. The Zone is a 40% carbohydrate, 30% protein and 30% fat eating plan that advocates only sparing use of grains and starches. The precise 0.75 protein to carbohydrate ratio required with each meal is promoted to reduce the insulin to glucagon ratio, which purportedly affects eicosanoid metabolism and ultimately produces a cascade of biological events leading to a reduction in chronic disease risk, enhanced immunity, maximal physical and mental performance, increased longevity and permanent weight loss. There is presently little scientific support for the connections made between diet, endocrinology and eicosanoid metabolism. In fact, a review of the literature suggests that there are scientific contradictions in the Zone Diet hypothesis that cast unquestionable doubt on its potential efficacy. The purpose of this review is to evaluate the scientific merit of the Zone Diet and its health claims in an effort to help delineate what is and what is not sound nutrition science.

• low carbohydrate diet
• 40/30/30 diet
• protein-carbohydrate ratio
• insulin-glucagon ratio
• eicosanoids

Key teaching points:

• The Zone Diet is a carbohydrate-restricted diet that postulates a connection between diet, hormones and eicosanoids that ultimately leads to improved health.

• There is no evidence that a 0.75 protein to carbohydrate ratio (40/30/30), whether eaten as a small test meal or in the form of a complete mixed diet, reduces the insulin response when compared to traditional dietary guideline meal/food intakes and may even potentially produce a larger area under the insulin curve.

• The Zone classification of eicosanoids as “bad” or “good” based on receptor binding or on gross physiological functions is oversimplified, but the recommendation to supplement the diet with omega-3 fatty acids or progenitors of series-1 eicosanoids has some documented health merit.

• Although carbohydrate, protein, insulin and glucagon can impact delta destaurase enzyme activity, those activities reported by the Zone clearly and selectively ignore the known effects of macronutrients and hormones that contradict the Zone theory.

• The scientific literature is in opposition to the purported benefits of adopting a Zone Diet for improved health.

Key teaching points:

• The Zone Diet is a carbohydrate-restricted diet that postulates a connection between diet, hormones and eicosanoids that ultimately leads to improved health.

• There is no evidence that a 0.75 protein to carbohydrate ratio (40/30/30), whether eaten as a small test meal or in the form of a complete mixed diet, reduces the insulin response when compared to traditional dietary guideline meal/food intakes and may even potentially produce a larger area under the insulin curve.

• The Zone classification of eicosanoids as “bad” or “good” based on receptor binding or on gross physiological functions is oversimplified, but the recommendation to supplement the diet with omega-3 fatty acids or progenitors of series-1 eicosanoids has some documented health merit.

• Although carbohydrate, protein, insulin and glucagon can impact delta destaurase enzyme activity, those activities reported by the Zone clearly and selectively ignore the known effects of macronutrients and hormones that contradict the Zone theory.

• The scientific literature is in opposition to the purported benefits of adopting a Zone Diet for improved health.

The author gratefully acknowledges the significant research assistance of Scott B. Robinson and the expert editorial assistance of Dr. Andrew J. Young, Chief, Military Nutrition Division, USARIEM.

The views and findings in this report are those of the author and should not be construed as an official Department of the Army position, policy, or decision unless designated by other official documentation. This work was approved for public release; distribution is unlimited.