Books: Enter the Zone, Mastering the Zone, and The Anti-Aging Zone

The Basic
Calories are distributed as 40% carbohydrate, 30% fat, and 30% protein at every meal and snack. In contrast, most "healthy diets" recommend calories be distributed as 55-60% carbohydrate, 12-20% protein and 20-30% fat.

How A Person Can Lose Weight On This Diet
Calories eaten must be below calories needed to maintain weight (i.e., low calorie). This is a low calorie diet. The higher protein level of the Zone Diet can also provide more satiety with meals and snacks. High carbohydrate food portions and sweets are restricted, so blood sugar surges after a high carbohydrate meal or sweet do not occur. This also helps control appetite.

Meal Plans
Protein needs are based on your lean muscle mass and physical activity level. Then you divide your protein into blocks, each block of protein equals 7 grams of protein. Once you know the required number of protein blocks you give yourself one carbohydrate and fat block for each protein block. Each meal has the same number of blocks for carbohydrate, protein, and fat. For example, lunch may include 3 blocks of protein, carbohydrates, and fat. You must keep this ratio for all meals and snacks. One block of carbohydrates is equal to 7 grams of carbohydrates while one block of fat is 1-½ grams.

Special Concerns
People who engage in endurance exercise are at risk for poor energy levels and muscular fatigue due to an inadequate carbohydrate intake.

Alcohol
The Zone recommends that alcohol may be good for you if taken in moderation (~1 drink per day) preferably red wine.

Claims

To be in the Zone you need a diet that is exactly 40% carbohydrate, 30% fat, and 30% protein at every meal and snack.
Insulin causes people to gain weight.
It is easy to lose weight on the Zone diet with "easy" rules.
A moderately active, 5-foot, 4-inch woman weighing 125 pounds with 23 percent body fat should eat just 775 calories per day.

Pros

Promotes eating fat and protein in the diet.
Addresses the importance of drinking plenty of water throughout the day.
Recommends exercise in combination with diet for weight loss.
Recommends snacking throughout the day.
Promotes low-fat protein foods.

Cons

Limits many grains (pastas, cereal, breads, potatoes), fruits (bananas and orange juice), and vegetables (carrots and sweet potatoes).
Complicated rules govern the diet. Dieters must calculate protein requirements based on complex charts and tables. Must also follow the "macronutrient block method" to determine how many "blocks" to eat per day and when to eat them.
Strict, controlled diet which does not work for the fast-paced lifestyles of today.
Recommends that for the average person a Zone-favorable diet should contain no more than 800 to 1,200 calories a day.
Food is treated like a medical prescription. "You must treat food as if it were a drug. You must eat food in a controlled fashion in the proper proportions- as if it were an intravenous drip."

Truth

Excess calories cause weight gain not specific carbohydrates.
Not one of the studies that Sears conducted to prove his diet works has been published.
Diets recommending less than 800 calories may be dangerous and should be medically supervised.
Anyone on a low-calorie diet is likely to lose weight.
May impair athletic performance.