The Zone diet is a diet popularized in books by Barry Sears. It advocates balancing protein and carbohydrate in 3:4 ratios. It is not primarily a weight-loss "diet", though it can be used quite successfully for that purpose.

The diet centers on a "40:30:30" ratio of calories obtained daily from carbohydrates, proteins, and fats, respectively. The exact formula is always under debate, but studies over the past several years (including a non-scientific study by the PBS documentary show Scientific American Frontiers) have shown that it can produce weight loss at reasonable rates.