Weight loss diets: The Zone Diet

The Zone Diet popularized by Barry Sears, Ph.D is based on the idea of keeping the levels of the hormone insulin with a desirable range, but especially not too high. Insulin has a role in the metabolism of carbohydrates, proteins and fats and is released by the body in response to food. Excessive levels of insulin are known to be a factor (one of many) in weight gain (especially fat gain) and various diseases, such as heart disease, hypertension and diabetes.

The main trigger of insulin release is the raise of blood sugar levels, which typically occurs after a meal high in carbohydrates, particularly those easy to digest and absorb. The sharper the rise, the more insulin is released.

The approach of the Zone Diet overlaps with that of low-carbohydrate diets in aiming at reducing the body's production of insulin. However, the Zone Diet avoids dramatic restrictions in the consumption of carbohydrates. The Zone Diet includes several steps aimed at reducing the release of insulin:

Restricting the amount of carbohydrate in the diet to about 40% of total calories (less carbohydrates enters the bloodstream)

Eating carbohydrates together with significant amounts of protein and fat, each constituting about 30% of total calories. This reduces insulin release by slowing the rate of carbohydrate absorption, making the blood sugar levels rise more blunt.

Finally, the Zone Diet recommends to mainly consume complex, slow-to-digest carbohydrates in order to blunting the rise of blood sugar after a meal, thereby reducing insulin release.

Another pillar of Zone Diet is improving the so-called eicosanoid balance, which, in essence, is a balance between the body's pro and anti-inflammatory mechanisms. While Dr. Sears claims that the 40/30/30 carb/protein/fat ratio itself helps achieve the optimum eicosanoid balance, there is no reliable evidence to support that. Additionally, Dr. Sears does suggest a more direct way of improving eicosanoid balance: fish oil supplements rich in omega-3 fatty acids. Omega-s fatty acids indeed increase the levels of anti-inflammatory eicosanoids and produce a variety of health benefits. In particular, they reduce the risk of heart disease, hypertension, depression and so-forth. However, there is no evidence that omega-3 supplements promote weight loss. If you plan to take a fish oil supplement, make sure to get a brand certified by a respectable independent laboratory to be free of mercury, otherwise it may do more harm than good.

Like any highly structured diet, the Zone Diet has its drawbacks, including the following:

The Zone Diet prescribes a set number of calories per meal and a set ratio of macronutrients. This scheme is hard to follow, especially in the long run.

Dining out, traveling and snacking may be difficult to incorporate in the Zone regimen.

Above average amount of protein places extra load on liver and kidneys.

The Zone Diet restricts calories to the degree than may make some people feel perpetually hungry.

There have not been any well-designed direct studies of the Zone Diet. Its cousins, the low-carbohydrate diets and low-calorie diets have been clinically studied (see the index of diet studies).

Bottom line

The Zone Diet attempts to achieve its goal through a combination of reducing insulin excess and cutting caloric intake by carefully structuring macronutrient composition and caloric value of meals. It avoids the trap of severely restricting food choices. In those who adhere to it diligently, the Zone Diet may produce a sustained weight loss. However, adhering to the Zone Diet is cumbersome, tedious and hard to incorporate into many lifestyles, especially for people who frequently travel or eat out. Relatively few people manage to diligently follow the Zone Diet in the long term.

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