What Is The Science Behind The Zone Diet?

When the book "The Zone" first hit the market in 1995, it became a "New York Times" best-seller. Dieters were eager to learn more about this new eating plan from Dr. Barry Sears, a former research scientist who shifted his focus from chronic disease to weight loss. The Zone Diet features protein-rich foods and considerable restriction of carbohydrates. As with many other diets that garner public attention, the science doesn't back up Sears' claims. Always speak with your doctor if you're considering starting any diet plan.

Zone Diet Basics

The Zone Diet is essentially a low-carb eating plan. Your daily food intake is made up of 40 percent carbs and 30 percent each of protein and fat. This is in contrast to normal guidelines for healthy eating, which recommend a diet of 55 percent carbohydrates, 15 percent protein and 30 percent fat. Lean protein sources -- including seafood, poultry and egg whites -- are key components of the Zone Diet. Nonstarchy vegetables are allowed, but most fruits and grains are restricted. Low-fat dairy is also permissible in small amounts.

Claims

Sears claims that hormones called eicosanoids have powerful effects on the body. These hormones are produced when you consume unsaturated fats. The premise behind the Zone Diet is that the eating plan helps maintain levels of these hormones, providing support for weight loss and immune function. Sears says that over time, cellular, or chronic, inflammation is responsible for obesity. The Zone Diet is aimed at halting this type of inflammation. Sears says the diet's ratio of carbs, protein and fat regulates insulin levels, thereby preventing the storage of body fat. Insulin is a hormone produced in the pancreas that helps keep blood sugar levels in check.

Research Findings

Research analyzing the Zone Diet has been unfavorable. Sears says the diet improves physical performance, making its effect on athletes of particular interest. One study, published in February 2002 in the "Journal of Strength and Conditioning Research," found that endurance athletes who followed the plan for a week actually became exhausted faster during activity than they did prior to starting the diet. The Zone Diet may perpetuate nutritional misinformation about carbohydrates. Sears' claims, according to Dr. Samuel N. Cheuvront, R.D., in a February 2003 "Journal of the American College College of Nutrition" article, are supported by poorly designed studies that rely heavily on anecdotal evidence.

Nutritional Concerns

Despite the focus on carbs and protein, the Zone Diet features a low-calorie eating plan of fewer than 1,500 calories a day. This is likely responsible for the weight loss that may occur while following the diet. The restrictive way of eating also raises nutritional concerns. Low carbohydrate consumption affects energy levels, because the macronutrient is the principal fuel source for the body. It may also lead to deficiencies in important nutrients such as iron, calcium and vitamin E. The strict diet is likely unsustainable, and may be unhealthy in the long term.

The Zone and Diabetes

No solid research suggests it could help control diabetes, but this low-carb diet may be effective for short-term weight loss -- up to one year -- in diabetics. The American Diabetes Association recommends, however, that those following such a diet have their cholesterol and triglyceride levels monitored regularly. The high protein intake could be a concern for patients with diabetic neuropathy, or kidney problems resulting from the disease. Medications used to treat diabetes may also need adjustment while following this type of diet, so working with a physician is vital.