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


  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

Further exerpt from the text of the review:


  "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."

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