There are no available studies of any kind that have looked at the Zone diet and its safety. Although all components of the diet have related literature that provides some insight into the potential risks and benefits of the diet, none have been studied well enough to provide firm recommendations.
Foods rich in vitamins and minerals, like calcium, iron, vitamins A, D, E and folic acid have limits set on them in the Zone diet. Foods rich in fiber, like whole grains and starches, are also limited. The Zone diet is considered a low carbohydrate diet plan. A qualified healthcare provider and nutritionist should be consulted before making decisions about diets.
Caution is advised in people with heart disease or high cholesterol due to the fat content of this diet.
Caution is advised in athletes in training due to the restriction in calories recommended by the Zone.
Recent research seems to indicate that a low total caloric intake is associated with longer life expectancy. Based on animal studies, animals eating calorie-restricted diets may live 1.5 to 2 times as long as animals eating high-calorie diets. Theoretically, similar effects may occur in humans. The caloric restriction recommended by the Zone diet is below that of the average American and may be of benefit in weight loss and if maintained over decades in increasing life expectancy. On the other hand, athletes in training will likely suffer from decreased performance if restricted to the low calorie diet recommended by the Zone.
Despite proposed benefits, currently there are no high quality clinical trials available about the Zone diet or similar diets consisting of the recommended 40% carbohydrates, 30% fat, and 30% protein. The Zone diet is quite complex in terms of caloric restriction, ratio of carbohydrates/protein//fat, spacing of meals, preferential intake of certain fats, and avoidance or inclusion of a few specific foods.