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The “Zone” Diet

The popular “Zone” program 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 for example 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. 56 That same year an NIH conference convened to address the concerns that such a diet would increase triglycerides and lower HDL. 130 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. 6 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. 185, 186 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, 11, 13, 15 and emphasizing the types of fat rather than total amount. 12, 187 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. 12, 154, 187 Eating smaller, more frequent meals spreads out the “nutrient load,” slows absorption of carbohydrates, helps stabilize insulin and glucose levels, 188 may prevent overproduction of free radicals, 112, 115, 189 and can lower total and LDL cholesterol and CHD risk. 190-192 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, 157, 158, 193 reduces hunger, 65, 194 stabilizes blood glucose, 65, 157, 194 lowers insulin levels, 65, 157, 194 improves lipid profiles, 65, 158 and reduces the risk factors for diabetes and heart disease. 65

A 1999 Harvard Medical School study led by David Ludwig demonstrated that diets with identical quantities of calories but different ratios of carbohydrates to protein to fat could affect how many calories are burned at rest. Subjects followed a high-glycemic index (high GI) diet (67:15:18) vs a low GI, approximately 40:30:30 (actually 43:27:30) diet. While they followed the high GI diet the subjects’ rate of burning calories while resting declined by 10.5 percent, but only by 4 percent during the low GI or 40:30:30. In other words, eating a high GI, low-calorie diet lowered the set point more than twice as a low-GI, 40:30:30 diet would. 195

Consistent with these findings, Donald Layman’s group from the University of Illinois, Urbana-Champaign, studied 24 middle-aged, overweight women. 193 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. 65 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. 194 ) 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. 65

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. 65

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. 196 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) 157, 158 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.

A recent study of 54 men and women with type 2 diabetes compared diets with a 40/30/30 vs. 60/15/25 ratio (carbohydrate/protein/fat) over a 12-week period. 197 For the first 8 weeks, each diet provided 1600 calories. They then continued for 4 weeks on the same diets but with a larger number of calories (the same for each group) to maintain their weight. The participants following each diet were given fixed menus and supplied key foods such as pre-weighed or fixed portions of beef and chicken for six meals per week. Overall, members of both groups lost about the same amount of total weight—about 11.5 lbs. However, women on the 40/30/30 diet lost twice as much total weight (approximately 12 vs 6 lbs) and twice as much abdominal fat (3 vs 1.5 lbs) compared with women following the lower protein-, lower fat-, and high carbohydrate-diet. Members of both groups experienced lower fasting blood glucose and insulin concentrations, reduced blood pressure, and lower levels of triglycerides. LDL cholesterol was reduced more on the 40/30/30 diet (5.7% vs 2.7%). Of the 30 participants who were taking oral medications and/or injecting insulin for their diabetes, 8 required lowering of their dosages at weeks 4 and 8 (5 from the 40/30/30 group vs 3 from the 60/15/25 group).

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. A review of the literature and clinical experiences support this approach.

Low Carbohydrate Diet—Atkins

The Atkins Diet is the most well-known reduced carbohydrate diet program that emphasizes a two-week induction phase designed to induce ketosis (not ketoacidosis) by limiting carbohydrates to no more than 20 grams per day. Gradually carbohydrates can be increased to up to 80 grams per day according to the individual’s needs. Currently, most of the studies that support the Atkins program have not yet been published. These include an independent study conducted by Gary Foster, a psychologist with the University of Pennsylvania’s Weight and Eating Disorders clinic. Compared to the USDA diet, the Atkins followers reportedly had greater long term compliance and lost more than twice as much weight as those who followed the USDA pyramid recommendations. Plasma HDL levels increased while triglycerides significantly decreased.

Results of a clinical trial of the Atkins diet led by Eric Westman, MD, MHS, assistant professor of medicine at Duke University, were presented at the recent Southern Regional Society of General Internal Medicine in New Orleans. Forty-one healthy, mildly obese male and female volunteers aged 18 to 65 completed the program. All were 20% to 50% above ideal body weight, had not followed another weight-loss program in the previous six months and were not taking any medication. Most of the subjects followed the “induction” phase of the Atkins program for the entire six-month period and received nutritional supplements. During the course of the study, blood pressure, heart rate, weight, waist size, percentage of body fat and urinary ketone level were among the measurements taken. All participants lost weight after 16 weeks, averaging an overall loss of approximately 1 to 3 pounds per week, leading to an average of 21 pounds lost over four months. There was also a significant 6.1% average drop in total cholesterol, a 39.9% average reduction in triglycerides, an 18.9% improvement in cholesterol/HDL ratio and a 7.2% average increase in HDL.

Keeping in mind that most Atkins followers restrict the ketosis stage for only the first two weeks or so, this phase often comes under attack by critics who deem ketosis harmful. Yet there is little to support that notion. In his recent New York Times Magazine article (July 7, 2002), Gary Taubes quotes NIH researcher and ketosis expert Richard Veech, “They’re (doctors) are always worried about diabetic ketoacidosis. But ketosis is a normal physiologic state. I would argue it is the normal state of man.” Veech goes on to call ketones “magic” and, per Taubes, has shown that “both the heart and brain run 25 percent more efficiently on ketones than on blood sugar.”

Sharman et al recently became the first to publish a study documenting the effects of a high-fat, low-carb, ketogenic diet on fasting and postprandial CVD biomarkers independent of weight loss. Eight healthy control subjects followed their habitual diet (47% carbs :17% protein :32% fat), while twelve switched from their habitual diet to a ketogenic diet (8% carbs: 30% protein: 61% fat). After six weeks, compared to the control group, those following the ketogenic diet had significant decreases in fasting serum triglycerides (-33%), postprandial lipemia after a fat-rich meal (-29%), and fasting serum insulin concentrations (-34%). There were significant increases in LDL particle size, and no change in the oxidative LDL concentrations. While HDL cholesterol increased, total and LDL cholesterol did not change significantly. Collectively, these responses in serum lipids, insulin and lipid subclasses to the ketogenic diet were favorable in terms of overall CVD risk profile. 198 This study is limited by its small size and simple design, however its findings are intriguing and worth considering.

While a recent diet advisory from the American Heart Association criticizes the Atkins approach by suggesting that the diet may not be ideal because it is high in saturated fat, animal protein, and cholesterol, 199 which has been discussed above. The advisory falls short of condemnation and admits that, “Although these diets may not be harmful for most healthy people for a short period of time, there are no long-term scientific studies to support their overall efficacy and safety.” 199 While this statement is correct, to my knowledge, the American Heart Association has not addressed a number of studies that show its dietary recommendations may worsen CVD risk by lowering HDL and raising triglycerides, total cholesterol, and insulin levels. 65, 125 One study cited to discredit the Atkins diet is no more than a computer generated, biased analysis that begins with the premise that a diet that is high in saturated fat and deviates from the USDA recommendations increases risk for CVD. 200 Clearly more long-term studies are needed to evaluate the long term effects of any diet, and, for the first time, NIH is funding a multi-center 5-year trial of the Atkins diet with 360 obese individuals. This standard should also apply to the USDA and AHA recommendations.

Food Provision

Providing food has been shown to reduce CHD risk 201-203 and may be a useful strategy for promoting weight loss. 204 In an 18 month study, food provision was associated with increased behavior compliance, increased nutrition knowledge, more regular meals and fewer snacks, reduced barriers to weight loss, and improved quality of foods in participants’ homes. 204

Alcohol

Several large prospective studies have demonstrated a reduced incidence of type 2 diabetes with moderate alcohol consumption but in the postprandial state, alcohol can result in reduced glucose disposal and increased blood glucose levels. 205, 206 A recent, large 12-year prospective study showed that frequent, low to moderate alcohol consumption reduced the risk of type 2 diabetes regardless of the type of beverage chosen or the total amount of alcohol consumed per week. Compared with zero alcohol consumption, consumption of 15–29 g/day of alcohol was associated with a 36% lower risk of diabetes 207 However, consistent with the literature, the evidence suggests a U- or J-shaped association between alcohol consumption and diabetes suggesting a delicate balance between beneficial and harmful effects of alcohol. 207

While epidemiologic data demonstrate that moderate alcohol intake is associated with improved insulin sensitivity in individuals without diabetes, only recently has there been a controlled-diet study addressing the effects of daily moderate alcohol consumption on fasting insulin and glucose concentrations and insulin sensitivity. 208 Nondiabetic postmenopausal women who consumed 30 g/d of alcohol (2 drinks per day) compared with 0 g/d reduced fasting insulin concentration by 19.2%, and triglyceride concentration by 10.3%, and increased insulin sensitivity by 7.2%.

Imhof et al. found a U-shaped association between alcohol consumption and concentrations of C-reactive protein (CRP) and leukocyte count as well as negative acute-phase reactants albumin and transferring 209 Consider that non-drinkers and heavy drinkers had higher CRP concentrations than moderate drinkers and the robust association between markers of inflammation, especially CRP, with endothelial dysfunction 210-212 and risk of CHD 110, 210 and type 2 diabetes. 111, 213 Perhaps an anti-inflammatory action of alcohol could contribute the link between moderate consumption and lower cardiovascular mortality and risk of diabetes. One must also weigh the dangers of potential abuse in recommending alcohol.

Next time we will examine current dietary trends and programs.

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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