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%.

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.

The Zone diet is based primarily on protein intake. Dr. Barry Sears, the author of The Zone Diet, suggests consuming between 0.8 and 1.0g of protein per pound of lean body mass. For a hypothetical individual weighing 180lb, with a body fat percentage of 12%, daily protein intake would work out between 127g and 158g per day. Because protein should represent 30% of daily caloric intake, daily fat consumption would be 70g, with carbohydrate intake at 211g. The daily energy requirement of the Zone diet for a 180lb 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.

A reduction in carbohydrate intake can harm your performance

Firstly, the Zone diet suggests a daily carbohydrate intake comprising 40% of total energy consumption. For a male weighing 180lb, this represents 211g 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 team. 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 intake

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.

The Zone diet can accelerate 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. 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 24% of their calories from fat, 46% from carbohydrate, and 29% from protein. The diet for subjects on the high carbohydrate diet consisted of 28% 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 (46/29/24) 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 (pronounced say-she-ate-ing) 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 days 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."