The Zone Diet Explained

The Zone essentially recommends a diet comprised of 40 percent carbohydrates, 30 percent protein, and 30 percent fat. Since the majority of calories are derived from carbohydrates it cannot, by definition, be a low-carbohydrate diet.  It also can contain less protein than the ADA’s recommendation. Since it is a calorie-restricted diet we can use Ms. Daly’s example of 1600 calories instead of 2500 calories. Thirty percent of 1600 calories represents 480 calories or 120 grams of protein vs 20 percent of 2500 calories (according to the ADA guidelines), which would represent 500 calories or 125 grams.   

In 1950 the ADA recommended a 40:20:40 macronutrient ratio. This changed slightly to 45:20:35 in 1971, and in 1986 it changed radically to a recommendation of 50-60 percent of calories as carbohydrates, 10-20 percent as protein, and less than 30 percent as fat. 1 That same year an NIH conference convened to address the concerns that such a diet would increase triglycerides and lower HDL. 2 This spawned a body of research around reducing carbohydrates and replacing them with monounsaturated fats. These studies resulted in improved glycemic control and lipid profiles in patients with type 2 diabetes. 3 This is part of the reason why the recommendations were subsequently changed in 1994 to allow for 10-20% protein and make up the difference with some unspecified combination of carbohydrates and primarily monounsaturated fat. Arguably too broad, these recommendations allow for a relatively low carbohydrate diet. 

While it is true that there are a lack of long term studies to support lower carbohydrate diets, the implication that the status quo or current “official” dietary recommendations are supported by data is somewhat exaggerated. There are few long-term studies documenting any diet’s benefits, and, until recently, there has been little if any data regarding the USDA recommendations. After following the diets of tens of thousands of men and women for more than eight years, McCullough of the American Cancer Society and her colleagues at Harvard Medical School recently concluded that closely following the USDA recommendations provided only slight protection from heart disease and little benefit in preventing major chronic diseases such as cancer. 4, 5 The data suggest that the guidelines may need to be revised, and several of these Harvard researchers recommend reducing high GI (rapidly absorbed) and total amounts of carbohydrates, 6-8 and emphasizing the types of fat rather than total amount. 9, 10 This encourages the avoidance of trans fats or partially hydrogenated oils hidden in margarines, fried fast foods, and commercially prepared foods; incorporating monounsaturated fat into the diet; and increasing omega 3s. 9-11 Eating smaller, more frequent meals spreads out the “nutrient load,” slows absorption of carbohydrates, helps stabilize insulin and glucose levels, 12 may prevent overproduction of free radicals, 13-15 and can lower total and LDL cholesterol and CHD risk. 16-18 All of these principles are consistent with the Zone diet. Rather than an inflexible, one-size-fits-all approach the 40:30:30, low glycemic concept is meant to be a great starting point for most people. Current research suggests this balance promotes lean body mass (muscle) and body fat weight loss, 19-21 reduces hunger, 22, 23 stabilizes blood glucose, 21-23 lowers insulin levels, 21-23 improves lipid profiles, 20, 22 and reduces the risk factors for diabetes and heart disease. 22  

In the interest of time and space I will not review each of these studies, although a few bear some elaboration. A research team at the University of Illinois-Champaign-Urbana studied 24 middle-aged, overweight women. 19 Half ate a 1660 calories-a-day diet consistent with the USDA Food Guide Pyramid—51 percent carbohydrates, 14 percent protein, and 34 percent fat (51:14:34) compared to the other half who ate approximately a 40:30:30 diet of equal total calories. After ten weeks, the 40:30:30 group lost only slightly more total weight (16.5 vs 15 lbs), but their diet was much more effective. The women who followed the 40:30:30 regimen lost 18 percent more body fat and 27 percent less muscle compared to the group following the traditional USDA-recommended diet. They also maintained higher levels of thyroid hormone suggesting that they were now burning more calories even while resting.  

Despres and his colleagues at the Quebec Heart Institute, recently compared the effects of a low GI—low fat—higher protein diet with the widely prescribed American Heart Association (AHA) phase 1 diet in overweight, otherwise healthy men. 22 The ratio of carbohydrate: protein: fat for the AHA diet was 55:15:30 compared to 37:31:32 for the low GI diet which was consistent with the Zone diet. When allowed to eat snacks, those following the low GI diet ate less (about 25 percent fewer calories) than when they were following the AHA diet. (Ludwig et al. also reported similar satiety and 81 percent fewer calories consumed after a single low-GI, 40:30:30 meal compared to a high-GI meal. 23 ) The low GI diet profoundly decreased triglycerides by an impressive 35 percent, increased the size of LDL particles, and reduced plasma insulin levels—all consistent with a reduction in the risk for CHD and diabetes. 22  

In contrast, while following the AHA diet but allowed to choose how much they ate, the subjects were hungrier, less satisfied, ate more, and their triglycerides rose 28% while their HDL-C decreased 10%, thereby increasing their risk factors for heart disease.  When the two diets were kept equal in the number of calories, and subjects were not allowed to eat snacks, the AHA diet performed poorly—it again lowered HDL and raised total cholesterol: HDL ratio, which are associated with greater CHD risk. Under these circumstances too, the AHA diet made people hungrier and less satisfied. Regarding the low GI, approximately 40:30:30 diet, the researchers noted that, to their knowledge, a reduction in consuming calories of that magnitude without inducing hunger was believed to be impossible without drugs, and that chronic hunger is a major barrier to compliance when patients are asked to follow a reduced-calorie diet. In addition to allowing people to eat fewer calories without hunger, after only six days, the low-GI diet improved the risk factors for CHD, diabetes, and obesity while the AHA diet worsened them. 22 

Ludwig’s group followed a total of 107 obese, but otherwise healthy children for four months. Sixty-four patients received a low GI diet (fewer total and fewer rapidly absorbed, highly refined carbohydrates) and 43 patients received a standard reduced-fat, higher carbohydrate diet. 24 After four months, patients in the low-glycemic group experienced a threefold greater decrease in body mass index (BMI) compared to the low fat group.  The low GI group had lost a mean of 4.5 lbs compared to a mean gain of body weight of nearly 3 lbs for the group following the reduced fat diet. 

Regarding the effects of a Zone-like diet specifically in patients with type 2 diabetes, Markovic et al had obese patients with mild type 2 diabetes follow a calorie-restricted diet (approximately 1100 to 1200 calories per day) with a macronutrient ratio (carbohydrate:protein:fat) close to approximately 40:30:30 (actually 38:33:29) 20, 21 These patients improved insulin sensitivity, glucose control, reduced triglycerides, and improved their cholesterol profiles.  By only the fourth day subjects improved their blood glucose and reduced their body fat, which the researchers attributed to the reduced consumption of carbohydrates. The increase in fat consumption also helped apparently by slowing the absorption of carbohydrates. 

For another time, we could debate the issues regarding truly high protein, low-carbohydrate diets, but let this article focus on the Zone diet—a calorie-restricted program consisting of moderate amounts of mostly low glycemic carbohydrates; adequate amounts of protein mostly from lean sources; and adequate to low fat emphasizing monounsaturates, omega 3s, and avoiding trans fatty acids. My review of the literature and personal experiences with patients support this approach, and I am happy to examine data to the contrary. 

Eric S. Freedland, MD graduated from University of Rochester School of Medicine in 1982, trained in internal medicine at Mt. Auburn Hospital in Cambridge, MA, and emergency medicine at Harbor-UCLA Medical Center in Torrance, CA, and  has held faculty positions at Harvard Medical School (1990-1991) and Boston University School of Medicine (1992-1997). Dr. Freedland has developed a nutrition-centered model of disease with a special emphasis on diabetes. A staunch advocate for prescribing lifestyle changes before drugs, Dr. Freedland has written and lectured extensively on this subject.    

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