Revealed! The truth about the Zone diet...

The Zone diet is the latest nutrition strategy that promises to improve athletic performance, reduce body fat and increase muscle mass. It recommends consuming 40% of your daily caloric intake in the form of carbohydrate, 30% as protein, with fat making up the other 30%.

The Zone diet
Despite its popularity, there is little evidence that the recommendations made in The Zone Diet can improve athletic performance. However, it is essentially a restricted calorie diet. For individuals wanting to lose body fat, there is no reason why the Zone diet would not prove effective.

This type of diet is nothing new. In fact, the Greek long-distance runner Stymphalos claimed that a meat based diet (rather than the vegetarian diet popular with most Greek Olympians) was responsible for his Olympic victories in the fifth century BC [2].

The Zone diet is based primarily on protein intake. Dr Barry Sears, the author of The Zone Diet, suggests consuming between 0.8 and 1.0 gram of protein per pound of lean body mass. For a hypothetical individual weighing 180 pounds, with a body fat percentage of 12%, daily protein intake would work out between 127 grams and 158 grams per day.

Because protein should represent 30% of daily caloric intake, daily fat consumption would be 70 grams, with carbohydrate intake at 211 grams. The daily energy requirement of the Zone diet for a 180 pound individual works out at approximately 2106 calories.

According to Dr Sears, this dietary regimen results in a greater delivery of oxygen to the working muscles, a condition known as "the Zone". However, Dr Sears has come in for a good deal of criticism from exercise scientists, mainly because the Zone diet directly challenges several long-standing assumptions.

Performance
Firstly, the Zone diet suggests a daily carbohydrate intake comprising 40% of total energy consumption. For a male weighing 180 pounds, this represents 211 grams of carbohydrate per day. Such a recommendation is in sharp contrast to the majority of scientific research, which shows that carbohydrate is essential for regular physical activity.

For example, a recent study compared the effects of different levels of carbohydrate intake on the performance of two Swedish ice hockey teams [1].

Both teams took part in two games separated by three days. During this three-day gap, the players were assigned to one of two groups. The first group consumed a normal mixed diet that provided around 40% of energy from carbohydrate. Group two had their diet supplemented with extra carbohydrate. Energy from carbohydrate in the second group represented 60% of total energy intake.

The study clearly showed an improvement in physical performance in the high carbohydrate group. Simply put, a diet containing only 40% of its calories from carbohydrate was insufficient to meet the energy needs of elite athletes.

Protein
The Zone diets' recommendations for daily protein intake are a little closer to the mark. The amount of protein required by those participating in regular exercise sessions remains a topic of considerable debate. Nevertheless, there is research to show that both endurance and strength exercise increase protein requirements.

For example, Dr. Peter Lemon and a team of researchers from Kent State University, Ohio, and McMaster University, Ontario, studied a group of 12 male subjects during two months of resistance training [3]. They found that a protein intake of 81 grams per day (1 gram per kilogram of bodyweight for a 180-pound male) results in a negative nitrogen balance.

Nitrogen balance is a measure of protein metabolism. A negative nitrogen balance indicates that the protein needs of the body are not being met. Over time, this may lead to reduced gains in muscle mass and strength.

However, Dr Lemon also reported that at higher protein intakes (2.6 grams per kilogram of bodyweight, which works out at 214 grams for a 180 pound male) nitrogen balance appeared to plateau. In other words, a protein intake of 2.6 grams per kilogram of bodyweight appears to represent nutritional overload.

Based on these findings, Dr. Lemon suggests 1.6-1.7 grams of protein per kilogram of bodyweight for individuals involved in strength training. For endurance athletes, the figure is a little lower — around 1.3 grams per kilogram of bodyweight.

For a 180-pound male, this gives a suggested protein intake of between 131 grams and 139 grams per day. This is not too different from the Zone diet recommendation of 127-158 grams per day.

Fat loss
The Zone diet does not provide enough energy to meet the needs of a competitive athlete. However, because it is essentially a restricted calorie diet, the recommendations made in The Zone Diet may prove useful for those wanting to lose weight. Its suggestions to consume high levels of protein may also serve to enhance fat loss.

A recent Danish study, published in the International Journal of Obesity, compared the effects of a high protein and a high carbohydrate diet on weight loss [4]. A group of 60 subjects followed a restricted calorie diet for six months.

The participants were assigned to either a high carbohydrate or high protein diet. Those on the high protein diet consumed approximately 29% of their calories from fat, 46% from carbohydrate, and 25% from protein. The diet for subjects on the high carbohydrate diet consisted of 29% from fat, 59% from carbohydrate, and 12% from protein. Scientists found that the high protein group lost almost twice as much fat as those on the high carbohydrate diet.

Notice the similarity between the nutrient distribution in the high protein diet (46/25/29) and the recommendations in the Zone diet (40/30/30). The group following the high protein diet consumed 11.3 calories for every pound of bodyweight each day — similar to the 11.7 calories per pound of bodyweight suggested by the Zone diet.

After analyzing the dietary intake of the groups, the research team realized those on the high protein diet had eaten less food. This accounted for the greater weight loss. There were several possible explanations for this reduction in food intake.

Protein has a higher "satiating effect" than carbohydrate. In other words, you feel less hungry when consuming a diet high in protein.

A high protein intake seems able to suppress the following day's energy intake to a greater extent than carbohydrate.

The digestion of protein requires far more energy than digesting carbohydrates. This may have slightly increased caloric expenditure in subjects on the high protein diet.

The bottom line
The Zone diet has come in for a good deal of criticism from exercise scientists. However, it is essentially a restricted calorie diet. For individuals wanting to lose body fat, there is no reason why the Zone diet would not prove effective.

It's unrealistic to expect that athletes will experience any significant improvements in performance as a result of the Zone diet. The recommendations for both carbohydrate and caloric intakes are not sufficient to meet the energy requirements of regular daily training.

In the words of Samuel Cheuvront, an exercise scientist at Florida State University, "When it comes to improving performance through diet, athletes would be well advised to steer clear of the Zone."

References
1. Akermark, C., Jacobs, I., Rasmusson, M., & Karlsson, J. (1996). Diet and muscle glycogen concentration in relation to physical performance in Swedish elite ice hockey players. International Journal of Sport Nutrition, 6, 272-284
2. Cheuvront, S.N. (1999). The zone diet and athletic performance. Sports Medicine, 27, 213-228
3. Lemon, P.R., Tarnopolsky, M.A., MacDougall, J.D., & Atkinson, S.A. (1992). Protein requirements and muscle mass/strength changes during intensive training in novice bodybuilders. Journal of Applied Physiology, 73, 767-775
4. Skov, A.R., Toubro, S., Ronn, B., Holm, L., & Astrup, A. (1999). Randomized trial on protein vs carbohydrate in ad libitum fat reduced diet for the treatment of obesity. International Journal of Obesity, 23, 528-533