The Zone diet is a diet popularized in books by Barry Sears.
It advocates balancing protein and carbohydrate ratios instead of caloric thinking as an approach to eating.
It is not primarily a weight-loss "diet" (though it can be used quite successfully for that purpose); rather it is a way of eating — the intake of food that produces the best results within the human body based on a hypothesis of how it has evolved to cope with varying food intake through the ages. "The Zone" is Sears's term for proper hormone balance.
When insulin levels are neither too high nor too low, and glucagon levels are not too high, then specific anti-inflammatory chemicals (types of eicosanoids) are released, which have similar effects to aspirin, but without downsides such as gastric bleeding.
Sears claims that a 30:40 ratio of protein to carbohydrates triggers this effect, and this is called 'The Zone.' Sears claims that these natural anti-inflammatories are heart and health friendly.