X-Message-Number: 12270 Date: Tue, 17 Aug 1999 03:16:10 -0700 (PDT) From: Doug Skrecky <> Subject: zone diet and athletic performance "The Zone Diet and Athletic Performance" Sports Medicine 27(4): 213-228 April 1999 Samuel N. Cheuvont Department of Nutrition, Food, and Exercise Sciences, Florida State University, Tallahassee, Florida, USA Abstract: The Zone diet is the latest eating regimen marketed to improve athletic performance by opposing traditional high carbohydrate sports diets. The 40/30/30 diet is centered primarily on protein intake (1.8 to 2.2 g/kg fat free mass; i.e. total bodyweight - fat weight) and promises a change in the body's insulin to glucagon ratio through its macronutrient alterations. Changes in the existing hormonal milieu are said to result in the production of more vasoactive eicosanoids, thus allowing greater oxygen delivery to exercising muscle. This favourable condition, known as the Zone, is anecdotally reported to benefit even the most elite endurance athletes. Applying the Zone's suggested protein needs and macronutrient distributions in practice, it is clear that it is a low carbohydrate diet by both relative and absolute standards, as well as calorie deficient by any standard. Reliable and abundant peer reviewed literature is in opposition to the suggestion that such a diet can support competitive athletic endeavours, much less improve them. The notion that a 40/30/30 diet can alter the pancreatic hormone response in favour of glucagon is also unfounded. The Zone is a mixed diet and not likely to affect pancreatic hormone release in the same way individual nutrients can. Although the postprandial insulin response is reduced when comparing a 40% with a 60% carbohydrate diet, it is still a sufficient stimulus to offset the lipolytic effects of glucagon. Many of the promised benefits of the Zone are based on selective information regarding hormonal influences on eicosanoid biology. Contradictory information is conveniently left out. The principle of vasodilating muscle arterioles by altering eicosanoid production is notably correct in theory. However, what little human evidence is available does not support any significant contribution of eicosanoids to active muscle vasodilation. In fact, the key eicosanoid reportedly produced in the Zone and responsible for improved muscle oxygenation is not found in skeletal muscle. Based on the best available scientific evidence, the Zone diet should be considered more ergolytic than ergogenic to performance. Further exerpt from the text of the review: Conclusion "The claim that competitive and elite endurance athletes can improve performance by consuming a diet of 40% carbohydrates within the confines of less than 2000 daily calories is not substantiated by reliable scientific evidence. After nearly 60 years of corroborative findings, it is instead quite clear that measurable improvements in endurance can only be achieved by following a high carbohydrate diet. It therefore remains fundamental to the training programme of endurance athletes to follow the recommended high carbohydrate diet which profoundly opposes the Zone. Although endurance athletes who neglect protein in order to maximise low fat, carbohydrate rich food choices can benefit from consuming more dietary protein, the Zone diet recommendations (1.8 to 2.2 g/kg/day) exceed even the highest reported needs (1.2 to 1.4 g/kg/day) suggested in the literature. In addition, any benefit of added protein would certainly be offset by the severe calorie and carbohydrate restrictions of the diet. While the lipid biochemistry related to the Zone diet is factual, the connections made between nutrition, endocrinology, lipid metabolism, and exercise physiology are extremely oversimplified and sometimes paradoxical. Although the best available research profoundly disputes any performance benefit in adopting such a diet, its popularity continues to grow under a cloud of seemingly scientific 'facts'. When it comes to improving performance through diet, athletes would be well advised to steer clear of the zone." Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=12270