About half of your diet should be meats and fats. The rest should be carbohydrates like fruit, potatoes and breads. That's the formula behind the Zone diet, based on the book by Barry Sears."He says if you eat your food in certain combinations you'll go into the zone," says nutrition expert Georganne Syler. The Zone is supposed to be that balance between mind and body where you'll lose weight. But the strict eating guidelines are so strict you practically have to use a calculator. The formula is 40% carbohydrates, 30% protein, 30% fat. "As a dietician we have to use calculations in prescribing diets for patients. It takes us 4 years to do this versus someone reading the book and knowing how to do some of these rules he describes," says nutrition expert Lori Pettet. But it's been a big success for Hollywood stars, like Jennifer Aniston, and it's growing in popularity in the Heartland. "We've heard of people loosing between 20-40 pounds in one month. It's a tremendous weight loss which can be very exciting," says Pettet. The pros of the Zone include the recommendation to drink lots of water, exercise and snack throughout the day, plus eating a varied diet. But nutrition expert Lori Pettet says it's not very safe. "One of the things with the Zone, is it's a very, very low calorie diet. Some menus he describes are only 800 calories and it's been proven that you have to eat 1200 minimum," says Pettet. Other Zone diet concerns include the strict guidelines that make it hard to follow. There's also a risk of heart disease from eating high protein meals and the loss of vitamins like calcium and potassium. The toughest part of the diet is tallying the right carb-protein-fat balance when you're making meal decisions. That can take lots of time and effort. Those are often the two things that make a diet tough to stick to.