The zone diet: is it suitable for athletes?

Dieting to improve performance

Is this the latest offering from the sci-fi channel? No, Zone is one of the popular diets that has taken the world by storm and is targeted, among others, at athletes. But is it really suitable for active people? Dr Louise Burke, head of the Australian Institute of Sport Nutrition, has conducted a thorough investigation into the claims made by Dr Barry Sears, author of The Zone Diet.

So what is the zone anyway? According to Dr Sears, to enter the zone you have to eat a meal or snack at least every five hours that conforms to the following profile: 30% of energy from protein, 40% from carbohydrates (particularly those with a low glycaemic index) and 30% from fat (particularly monounsaturated fats). Although several companies in the USA manufacture ready-made ‘zone’ meals and nutrition bars, Dr Burke believes that it would be difficult to actually achieve the zone formula in everyday life.

If you can achieve the right balance, does it work? Most scientists are sceptical about the claims made for the diet, and Dr Burke is concerned that athletes trying to follow it strictly would be in a self-defeating state of energy deprivation. In simple terms, the diet is an energy-restricted one; Dr Burke calculates that a lean male endurance athlete weighing 64kg would have an energy intake of just 1,735 calories per day on the diet, while a female recreational athlete weighing 55kg would take in a mere 1,065 calories. The zone is not a magic formula, simply a low-calorie diet. It is true that some athletes may want to shed body fat, but there are better ways of doing so than this. And the book fails to mention how the diet would help athletes who don’t want to lose body fat and need to remain in energy balance.

Dr Burke points out that there are no published studies to support any benefits of the zone diet on athletic performance, and concludes that the 40:30:30 diet is a well-marketed nutrition craze.
Sports Coach, vol 24 (2) pp17-19

Nick Grantham