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Health Advantages and Disadvantages of Weight-Reducing Diets: A Computer Analysis and Critical Review

Metabolic Research Group, Veterans Affairs Medical Center; Department of Internal Medicine, College of Medicine, and Graduate Center for Nutritional Sciences, University of Kentucky, Lexington, Kentucky (J.W.A., E.C.K.)
Clinical Nutrition & Risk Factor Modification Center, St. Michael’s Hospital, Department of Nutritional Sciences, Faculty of Medicine, University of Toronto, Toronto, Ontario, CANADA, (D.J.A.J.)

Address reprint requests to: James W. Anderson, MD, B402, VA Medical Center, Medical Service 111C, 2250 Leestown Road, Lexington, KY 40511. E-mail: jwandersmd{at}aol.com

	ABSTRACT

TOP ABSTRACT INTRODUCTION METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
Background: Some weight-loss diets are nutritionally sound and consistent with recommendations for healthy eating while others are "fad" diets encouraging irrational and, sometimes, unsafe practices.

Objective: The purpose of the study was to compare several weight loss diets and assess their potential long-term effects.

Design: Eight popular weight-loss diets were selected (Atkins, Protein Power, Sugar Busters, Zone, ADA Exchange, High-Fiber Fitness, Pritikin and Ornish) to be non-clinically analyzed by means of a computer to predict their relative benefits/potential harm. A summary description, menu plan and recommended snacks were developed for each diet. The nutrient composition of each diet was determined using computer software, and a Food Pyramid Score was calculated to compare diets. The Mensink, Hegsted and other formulae were applied to estimate coronary heart disease risk factors.

Results: Higher fat diets are higher in saturated fats and cholesterol than current dietary guidelines and their long-term use would increase serum cholesterol levels and risk for CHD. Diets restricted in sugar intake would lower serum cholesterol levels and long-term risk for CHD; however, higher carbohydrate, higher fiber, lower fat diets would have the greatest effect in decreasing serum cholesterol concentrations and risk of CHD.

Conclusions: While high fat diets may promote short-term weight loss, the potential hazards for worsening risk for progression of atherosclerosis override the short-term benefits. Individuals derive the greatest health benefits from diets low in saturated fat and high in carbohydrate and fiber; these increase sensitivity to insulin and lower risk for CHD.

Key words: diet fads, diet, weight loss, obesity, cardiovascular disease, coronary disease

	INTRODUCTION

TOP ABSTRACT INTRODUCTION METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
Overweight and obesity are rapidly increasing in prevalence and are becoming major health problems in the US [1,2]. Over 50% of Americans are overweight [1], and the preventable deaths attributed to obesity exceed 300,000 per year [3]. The economic burden in the US approximates $100 billion [4]. Current treatment approaches are not very effective and many overweight and obese individuals attempt to achieve healthier weights with a wide variety of diets [5]. Of the many available diet approaches, some are nutritionally sound and consistent with recommendations for healthy eating for most adults while others are "fad" diets endorsing irrational and, sometimes, unsafe practices. Since the energy provided by any diet is the predominant determinant of body fat losses, we compared some of the potential health advantages and potential health risks of popular diets used for weight-reduction.

Popular diets today include these: "Dr. Atkins’ New Diet Revolution" [6], "Protein Power" [7], "Sugar Busters!" [8] and "The Zone" [9]. Moderate diets consistent with consensus nutrition recommendations of many expert panels [10–20] are "Dr. Anderson’s High-Fiber Fitness Plan" [21] and the American Diabetes Association/American Dietetic Association (ADA) Exchange Diet [22]. The consensus recommendation of most expert panels is to consume a diet consisting of <30% of total energy from fat, <10% from saturated fat, and to consume <300 mg cholesterol daily [10–20]. Popular low-fat diets are the "Pritikin Diet" [23] and the "Ornish Diet" [24]. Since all of these diets can be used for weight reduction, we calculated the nutrient content of all diets using energy-restricted menu plans providing the same energy intake and, also, assessed potential effects of their long-term use with weight-maintaining energy intakes.

	METHODS

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Selection of Diets for Evaluation
We selected popular low-carbohydrate, weight-loss diets based on book sales and general visibility in the media. The Atkins diet [6,25] has been popular for more than 25 years. Protein Power [7] has been the best-selling diet book at Joseph-Beth Booksellers in Lexington, KY. Sugar Busters! [8] has been on most best seller lists for non-fiction. Reported sales for The Zone exceed one million copies [9]. We compared these diets with the ADA Exchange diet [22] and Dr. Anderson’s High-Fiber Fitness Plan [21]. For contrast with high-fat, high-protein diets, we assessed the Pritikin [23] and Ornish diet [24].

Summary Description
We developed a summary description of the rationale for the diet. We used the authors’ terminology and descriptions, but did not include statements that are not generally accepted. We reserve the words "recommend" or "recommendation" for the guidelines endorsed by health authorities or expert panels [10–20] and sometimes use the word "consensus" to clarify these recommendations.

Menu-Plan Selection
We developed seven different daily menu plans for each diet to provide 1600 kcal per day. A 1600 kcal diet was chosen for comparison because several diets suggested energy intakes at this level. Since some diets did not provide serving sizes, we selected common portion sizes. Sample menus illustrate types of foods advocated.

Snacks, "Free Foods" and "Foods Not Suggested"
Commonly suggested snacks are outlined. "Free foods" refer to foods that can be eaten without concern for decreasing adherence to the diet. "Foods Not Suggested" indicate foods the authors suggest should be avoided or used in moderation.

Nutrient Composition
The approximate nutrient and fiber contents were calculated for each diet using Nutritionist IV (Nutritionist IV Diet Analysis, First Data Bank Division, Hearst Corp., San Bruno, CA). The nutrient composition of the seven daily menu plans for each diet was calculated and averaged to provide the daily values. Grams of nutrients per day were adjusted to achieve a daily intake of 1600 kcal. The percentage nutrients are the actual percentages for the seven-day menu.

Food Pyramid Score
Servings of grains, vegetables and fruits for each diet were compared to consensus recommendations [10–20] or consumption of these servings: grains (bread, breakfast cereal, rice and pasta) 6, vegetables 3 and fruits 2 [17]. We calculated the "Positive" score by adding number of servings from the bottom two tiers of the pyramid (grains, vegetables and fruits). Since the consensus recommends [10–20] limiting fat intake to two servings per day and meat consumption to three servings per day, we attributed negative points to intakes >2 servings of fat or >3 servings of meat. The "Negative" score is the sum of servings of fat and meat that exceeded recommended levels. The Food Pyramid Score is the sum of the Positive and Negative scores.

Effects of Weight-Maintaining Diets
We estimated the impact of maintaining these diet patterns for long-term periods using a weight-maintaining energy intake of 2000 kcal/day; we calculated nutrient content by multiplying values for the 1600-kcal diet by 1.25. As a reference diet we selected a previously constructed "typical American diet" [26]. Since data on the effects of most of these diets in a weight-maintenance mode are not available, we used formulae to estimate the impact on CHD risk factors. We selected a serum cholesterol value of 200 mg/dL as "baseline" and computed percentage changes from this value.

Dietary saturated fat [27], cholesterol [28] and soluble fiber [29–31] have the greatest impact on serum cholesterol concentrations. Keys and colleagues [32], Hegsted and colleagues [33] and Howell and colleagues [34] have developed equations to estimate the effect of dietary fatty acid intake on serum cholesterol concentrations. The equations of Keys et al. [32], Hegsted et al. [33], and Mensink and Katan [27] provide similar estimations, while the equation of Howell et al. [34] provides smaller estimated changes. We selected the equation of Mensink and Katan [27] to estimate the effects of fatty acids on the changes in serum cholesterol concentrations that would be associated with these dietary changes. This equation is:

cholesterol is change in serum cholesterol values in mg/dL, S is change in percentage of energy from saturated fatty acids, M is change in energy from monounsaturated fatty acids, and P is change in energy from polyunsaturated fatty acids. As also indicated by the authors [27], estimates using this equation are of similar magnitude to those of Keys [32] and Hegsted [33].

Hegsted and colleagues [28,33] and Howell and colleagues [34] have developed equations to estimate the effects of dietary cholesterol on serum cholesterol concentrations. In this analysis, the simple Hegsted formula [28] was used which indicates that every change in dietary cholesterol of 1 mg/1000 kcal would predict a change in serum cholesterol of 0.097 mg/dL. This formula was chosen because changes in serum cholesterol values were intermediate between those reported earlier by Hegsted et al. [33] and those reported by Howell et al. [34].

Soluble fiber intake also significantly decreases serum cholesterol values [29–31]. The recent report by Brown and colleagues [31] provides a conservative estimate of effects of changes in soluble fiber intake and serum cholesterol values. Since our previous studies [26] indicate the soluble fiber content of mixed diets across an array of different dietary patterns is approximately 30% of total fiber, we calculated the soluble fiber content of these diets as total dietary fiberx0.3. The Brown formula [31] indicates that changes in soluble fiber intake of 1 gram/day are associated with a 1.7 mg/dL change in serum cholesterol values.

Higher carbohydrate diets may increase serum triglyceride values. Mensink and Katan [27] developed a formula for calculating the effects on serum triglycerides produced by replacing fatty acids with carbohydrate. This formula is as follows:

in serum triglycerides in mg/dL with C=carbohydrate (% energy), S=saturated fat (% energy), M=monounsaturated fatty acids (% energy) and P=polyunsaturated fat (% energy).

	RESULTS

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Summary Descriptions and Menu Plans
All authors stress the importance of physical activity, smoking cessation and other healthy lifestyle changes. We limit this review to nutrition guidelines. After calculating the nutrient content for seven-day menu plans we, developed a "representative one-day menu plan" for each diet. This representative menu plan illustrates the types of foods suggested and provides approximately 1600 kcal per day (Table 1).

Protein Power, written by Michael R. Eades, MD, and Mary Dan Eades, MD, [7], closely resembles the Atkins diet in nutrient composition. They identify insulin as the culprit for obesity. They believe high levels of insulin cause metabolic disturbances in the body leading to elevated blood pressure, cholesterol and triglycerides, diabetes and obesity. They suggest restricting carbohydrate intake will overcome these metabolic disturbances and alleviate medical problems. Guidelines concentrate on the amount of protein rather than fat consumed. Their book outlines methods to determine the amount of protein to consume and gives instructions for planning meals around grams of protein with restriction of carbohydrates to 30 grams/day. They emphasize high-fat food choices but permit limited amounts of fruits and vegetables.

Sugar Busters!, written by H. Leighton Stewart, Morrison C. Bethea, MD, Sam S. Andrews, MD, and Luis A. Belart, MD, [8] states "sugar is toxic!" As do the authors of the previous diet books mentioned, they believe that insulin insensitivity causes obesity and non-insulin-dependent diabetes. The diet focuses on reducing high-glycemic carbohydrates (insulin-stimulating carbohydrates) to lower insulin levels and decrease insulin-resistance. They state "calories per se are not as important as the types of food we eat, how we eat them, and what metabolic processes control their assimilation." The concept is to consume foods with a low-glycemic index (high-fiber vegetables, fruits and whole grains), lean meats and fats in moderation. White bread, white rice, potatoes, corn, beets, carrots and many other root vegetables are not allowed. These authors advocate moderate alcohol consumption, primarily in the form of red wine, because "compared to many other carbohydrates, alcohol is less fattening" and "a glass of wine has fewer calories than a slice of white bread." These statements are inaccurate because alcohol provides 7 kcal/g compared to carbohydrate, which provides 4 kcal/g, and a 5 oz glass of wine provides 100 kcal, while a 1 oz slice of bread providing 70 kcal.

Barry Sears, Ph.D., wrote The Zone [9] to promote a high-protein, modestly restricted carbohydrate diet. He states "much of the current wisdom is dead wrong." He suggests "if you follow extremes of today’s fashionable, low-fat, low-protein, high-carbohydrate diets, you may actually be putting yourself in danger." He states that "eating fat does not make you fat," but "it’s your body’s response to excess carbohydrate in your diet that makes you fat." Sears encourages people to eat in such a manner that achieves a "metabolic state" which enables the body to work at peak efficiency and claims that important fundamental components of this "optimal metabolic state" are determined by specific eicosanoids produced in the body. He postulates that production of health-promoting eicosanoids results from consumption of the appropriate balance of macronutrients (30% protein, 40% carbohydrate and 30% fat) at each meal. The Zone diet focuses on lean meats and can include three servings of fowl per day but avoids high-fat animal products, most grain products, starchy vegetables and some fruits.

The ADA Exchange Diet [22] is the recommendation for healthy eating from the American Diabetes Association (ADA) and the American Dietetic Association (ADA). Many dietitians and nutritionists use these diet principles as guidelines for weight-loss and weight-maintenance diets. The ADA recommends an intake of approximately 50% to 55% carbohydrate, 10% to 20% protein and fewer than 30% of calories from fat for most individuals [15]. Foods are categorized into exchanges of fruits, vegetables, meats, dairy, carbohydrates and fats. Individuals are encouraged to consume a specified number of items from each exchange depending on the person’s caloric intake and individualized needs. The ADA counsels avoidance of high fat animal products and limits intake of oils.

James W. Anderson, MD, and Nancy J. Gustafson, MS, RD, wrote Dr. Anderson’s High-Fiber Fitness Plan [21]. Subsequently, Anderson and Maury M. Breecher, PhD, wrote "Dr. Anderson’s Antioxidant, Antiaging Health Program" [37]. These authors advocate the generous intake of vegetables, fruits and high-fiber foods with a moderate restriction of fat intake. Unlike the four popular diet books summarized above, this book emerged from research experience indicating that high-carbohydrate, high-fiber, low-fat diets increase insulin sensitivity, lower insulin needs in diabetic individuals and improve serum lipids [38–40] and that high-fat diets lead to insulin resistance [39–41]. Anderson recommends a wide variety of vegetables, fruits, whole grain products and low-fat animal products.

Nathan Pritikin wrote The Pritikin Permanent Weight-Loss Manual [42] and, subsequently, Pritikin and Patrick M. McGrady, Jr., MD, wrote The Pritikin Program for Diet and Exercise [23]. This diet is low in fat, cholesterol, protein and highly refined carbohydrates, but high in complex carbohydrates and fiber. Nathan Pritikin visited one of us (J.W.A.) in 1974 and expressed the feeling that the "High-Carbohydrate, High-Fiber (HCF) Induction Diet" (70% of energy as carbohydrate, 70 grams of fiber per day [38]) closely resembled the Pritikin diet [43]. Pritikin advocated an intake of 5% to 10% of energy from fat, 10% to 15% from protein and the remaining 80% as carbohydrates (specifically, complex carbohydrates). He suggested that eating large amounts of fat causes damage to body tissues by depriving them of oxygen, raises serum cholesterol and uric acid levels and impedes carbohydrate metabolism causing insulin resistance. Meat and fish are limited to four ounces per day, and most foods selected are plant-based, high-fiber foods that are low in "energy density". Barnard and colleagues [44–46] reported on the short-term and long-term health benefits achieved by using the Pritikin diet, weight loss and increased physical activity.

Eat More, Weigh Less by Dean Ornish, MD, [24] stresses a plant-based, vegetarian diet that is low in fat and high in complex carbohydrates and fiber. Ornish advises individuals to consume <10% of their energy intake from fat. He suggests, accurately [47,48], that fat is the culprit for weight gain and reasons that the body converts dietary fat into body fat more efficiently. Ornish and colleagues [49] report that the Ornish diet, weight loss, regular exercise and meditation are associated with regression of coronary atherosclerotic disease.

Snacks
Authors made suggestions for snacks that they believed to be health promoting (Table 2). Atkins and the Eadeses endorse meats, cheeses and high fat foods as snacks. The Sugar Busters authors suggest snacks such as fruits and nuts. Sears approves snacks consisting of cottage cheese with fruit and plain low-fat yogurt or milk. The ADA, Anderson, Pritikin, and Ornish all suggest fresh fruits, vegetables, nonfat yogurt and whole grains and breads for snacks.

Foods Not Suggested
Many diets proscribe certain foods (Table 2). Atkins advises that fruits, breads, grains, starchy vegetables and most dairy products (except heavy cream and certain cheeses) be avoided. The Sugar Busters authors advocate avoiding white rice, white bread, starchy vegetables and all refined sugar products. Sears advises that individuals avoid consuming fatty meats, some dairy products, starchy vegetables, some fruits, most grains and breads. The ADA, Anderson, Pritikin and Ornish, in contrast, advise that most "free foods" in the Atkins diet be avoided or limited. The low-fat diets do not advise foods such as fats, oils, refined sugars and whole-fat dairy products.

Nutrient Analysis
Seven-day menu plans from each diet were analyzed and summarized in Table 3. The Atkins diet provided the largest amount of total fat (104 grams/day providing 59% of energy), saturated fat (47 grams/day) and cholesterol (924 mg/day) and the lowest intake of carbohydrate (22 grams/day providing 5% of energy) and dietary fiber (4 grams/day). Atkins suggests that an individual consume <3 servings of vegetables per day and no fruit or milk. With >17 meat exchanges/day, the Atkins diet provides 35% of its energy from protein. The Protein Power diet advocates 53% of energy as fat. Although its proponents suggest <10 grams of carbohydrate per day, our analysis indicates the diet provides 33 grams of carbohydrate per day (8% of energy). They also approve more than 17 meat exchanges per day to provide >140 grams per day of protein (35% of energy). Their diet includes approximately 5 vegetable exchanges per day and no fruit or dairy products.

At 1600 calories the ADA Exchange diet includes 9 starch, 4 fruit, 4 vegetable, 5 meat (primarily lean meat), 2 milk (skim), and 6 fat exchanges. This diet provides 35 grams of fat per day (20% of energy) of which 11 grams were of saturated fat. The ADA diet provides 82 grams of protein (20% of energy) and 239 grams of carbohydrate per day (60% of energy). The macronutrient distribution of the High Fiber diet is similar to that of the ADA Exchange diet (63% carbohydrate, 16% protein and 21% fat). The major difference is that the High Fiber diet contained 58 mg of cholesterol and 29 grams of dietary fiber. Anderson advises consuming one high fiber cereal, five fruits, five vegetables and eight additional starches (primarily of whole grains). Meat is allowed but he favors the use of fish and shellfish at least twice a week and dried beans and legumes several times per week.

The Pritikin diet provides 292 grams of carbohydrate (73% of energy) and 17 grams of fat (9% of energy) daily. Pritikin endorses the daily intake of two or more kinds of whole grains, 2 raw vegetables, and 3 to 4 fresh fruit servings. He also suggests eating beans and peas one to three times a week, limiting protein from animal sources and avoiding sugar or honey. The Ornish diet provides less fat than any of the diets reviewed, with only 12 grams/day of fat (7% of energy). Ornish advocates unlimited quantities of low-fat, high-fiber, complex carbohydrate foods such as bean and legumes, fruits, grains and vegetables. He suggests using low-fat dairy products in moderation and avoiding all meats, oils, nuts and seed, alcohol, and high fat fruits and vegetables (avocados and olives).

Food Pyramid Score
The Atkins and Protein Power diets provide fewer servings of grains, vegetables and fruits than the minimum recommendations of 11 servings per day (Table 4). Sugar Busters and The Zone diets hover at the recommended level. ADA Exchange and the High-Fiber diets substantially exceed the recommendations and the Ornish and Pritikin diets most strongly encourage "eating at the bottom" of the food pyramid (Table 4). The Food Pyramid Scores for the various diets were as follows: Atkins, -23; Protein Power, -21; Sugar Busters, -3; Zone, -4; ADA, +9; High Fiber, +12; Pritikin, +26, and Ornish, +25 (Fig. 1).

View larger version (40K): [in this window] [in a new window]   Fig. 1. Assessment of diets comparing a calculated Food Pyramid Score. The Food Pyramid Score is determined for each diet by the number of servings of grain, fruit, vegetable, fat and meat to consensus recommendations.

The Brown formula estimates that soluble fiber from the diets would affect serum cholesterol values as follows: Atkins, +3 mg/dL (+2%); Protein Power, -1 mg/dL (-1%); Sugar Busters, -9 mg/dL (-5%); Zone, -6 mg/dL (-3%); ADA, -8 mg/dL (-4%); High Fiber, -12 mg/dL (-6%); Pritikin, -20 mg/dL (-10%); Ornish, -26mg/dL (-13%).

We have also summed these three changes to give an aggregate estimate of the effects of these diets on serum cholesterol values (Fig. 2). The effects of changes in fatty acid, cholesterol and soluble fiber intake on serum cholesterol values compared to the reference American diet for the diets are as follows: Atkins +51mg/dL (+26%); Protein Power, +18mg/dL (+9%); Sugar Busters, -24mg/dL (-9%); Zone, -26mg/dL (-13%); ADA, -35 mg/dL (-18%); High Fiber, -46mg/dL (-23%); Pritikin, -55mg/dL (-28%); Ornish -63mg/dL (-32%). (Fig. 2) These predicted changes in serum cholesterol values are in the range observed in three metabolic-ward feeding studies [38–40]. We compared control and high-carbohydrate (70% of energy), high-fiber (70 grams/day) diets and noted that serum cholesterol concentrations were 45 to 59 mg/dL (22 to 28%) lower on the high-carbohydrate, high-fiber diets than the control diets. The current Ornish and Pritikin diets resemble the high-carbohydrate, high-fiber diets used in our metabolic ward research. Although long-term data for the Ornish diet [49] and the Pritikin diet [44–46] are available, these interventions included increased physical activity and weight loss to enhance the diet effects; because of physical activity and weight changes, these reported data cannot be directly applied to our current analyses for weight-maintaining diets.

View larger version (32K): [in this window] [in a new window]   Fig. 2. Diet effects on serum cholesterol levels for weight loss diets. Shown by predicted % change in serum cholesterol levels as determined by the summation of values predicted by the equations of Keys et al. [32], Hegsted et al. [33] and Mensink and Katan [27].

	DISCUSSION

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An effective weight-reduction regimen includes a reduced-energy intake with adequate nutrition as well as an increase in physical activity. Loss of body fat is proportional to energy deficits, and no specific distribution of carbohydrate, protein and fat has been significantly related to more rapid weight loss than other distributions. Higher protein intakes may have greater satiating effects than higher carbohydrate intakes, but further research is required in this area [55,56]. However, this satiating effect of protein may contribute to the popularity of some of the popular high protein diets.

The protein content of the four diets (Atkins, Protein Power, Sugar Busters and The Zone) are almost double the Recommended Daily Allowances of 0.8 grams/kg or 56 to 80 grams for persons weighing 70 to 100 kg. High animal protein intakes have been linked to higher risks for CHD [57] and cancer [47,58]; however, these observations are questioned because appropriate adjustments for types of fat intake were not made [59]. High animal protein intakes also have been linked to higher risks for osteoporosis [60], and renal disease [61], but both of these areas are controversial [62,63]. Persons with diabetes or hypertension who have increased risk for renal disease may be especially vulnerable to the detrimental effects of large amounts of animal protein intake on renal function [63–65]. Thus, while we have concerns about long-term animal protein intakes exceeding 100 grams per day, at the present time we do not have documentation that this poses health hazards.

Low-carbohydrate diets may be accompanied by greater weight loss than other diets because of greater loss of water. Glycogen is hydrated with 2 to 3 grams of water per gram of glycogen, while fat stores contain only 0.5 grams of water per gram of fat [66]. Thus, high fat, low-carbohydrate diets deplete muscle and liver glycogen stores rapidly and facilitate rapid weight (water) loss. This rapid weight loss may contribute to the popularity of very low carbohydrate diets. Furthermore, initial weight loss on low carbohydrate diets may be enhanced by an exaggerated diuresis related to decreased postprandial serum insulin levels. Insulin promotes water retention through its antinatuiresis effects [67]. When individuals commit themselves to a weight-loss program, they commit themselves to paying attention to what they eat and avoiding unplanned eating episodes. Any diet that proscribes certain foods and focuses on intake of specific foods may enable motivated individuals to lose weight. When the diet has unusual features—such as having a bacon cheeseburger without a bun or steak without bread or potatoes—the diet may decrease energy intake because it alters usual patterns of eating. Less palatable diets may promote greater weight losses because individuals decide not to eat the full amount of food suggested.

While weight loss decreases serum cholesterol concentrations [68], the Atkins diet increases serum cholesterol despite weight loss [69]. Furthermore, long-term use of very high fat diets for weight maintenance would further increase serum cholesterol concentrations. Atkins suggests that lipid profiles improve with the use of low-carbohydrate, high-fat diets [6]; however, a study conducted by LaRosa and colleagues [69] examined the effect of lipid changes after following the Atkins low-carbohydrate, high-fat diet for four weeks. Despite a weight loss of 4.1kg, total cholesterol insignificantly increased 12.3mg/100mL. Significant changes in LDL cholesterol (+23mg/100mL) triglycerides (-45.0mg/100mL), free fatty acids (+426mEq/L) and uric acid (+1.8mg/100ml) were seen.

Recently Lichtenstein and Van Horn [70], for the Nutrition Committee of the American Heart Association, concluded: "There is overwhelming evidence that reductions in saturated fat, dietary cholesterol, and weight loss offer the most effective dietary strategies for reducing total cholesterol, LDL-cholesterol levels, and cardiovascular risk." Our calculations suggest that long-term use of the Atkins diet would increase serum cholesterol values by 25%, while long-term use of the Ornish diet would decrease serum cholesterol concentrations by 32%. Since every 1% change in serum cholesterol values are estimated to produce a 2% to 3% change in risk for CHD [71], long-term use of the Ornish diet might decrease risk for CHD by >60%, while long-term use of the Atkins diet might increase risk for CHD by >50%.

While LDL-cholesterol appears to be the most atherogenic lipoprotein particle [72], we did not have comprehensive formulae to estimate effects of fatty acids, dietary cholesterol and dietary fiber on serum LDL-cholesterol concentrations. The Mensink and Katan formula [27] suggests that changes in serum LDL-cholesterol closely parallel changes in total serum cholesterol values.

Interpreting the effects of diet on serum HDL-cholesterol concentrations is problematic. At least nine different HDL-particles have been identified [73]. The "HDL₂" particles are reported to be protective from atherosclerosis while the "HDL₃" particles are considered to be neutral [74]. The apolipoprotein "A-I only" particles are considered to be protective while the apolipoprotein "A-I/A-II" particles are considered to be neutral or even atherogenic [75,76]. High saturated fat diets clearly increase HDL-cholesterol concentrations [27,77], but the effects of these changes on risk for CHD are unclear. In contrast, increasing carbohydrate intake at the expense of fat intake decreases serum HDL-cholesterol values, but the effects on risk for CHD are unclear [27,75].

The diet effects on serum triglyceride levels are also complex. High fat diets readily decrease fasting serum triglycerides values [39,69]. High carbohydrate, low fiber diets increase fasting serum triglyceride values [38,39], as predicted by the Mensink and Katan equation [27]. However, high carbohydrate, high fiber diets either do not effect or decrease fasting serum triglyceride levels [38,39]. In one of our studies of free-living subjects [41], high-carbohydrate, high-fiber diets were associated with slight increases in fasting serum triglycerides. In our metabolic ward studies [38–40] and a long-term study of free-living subjects [78], high-carbohydrate, high-fiber diets were associated with stable or lower fasting serum triglyceride values (see Table 5). In other studies [51–53], especially those using traditional high-fiber, low-glycemic index foods, significant reductions in fasting serum triglyceride values were reported. Chandalia and colleagues [79] showed that high-fiber diets lower triglycercide values by 10.2% along with total cholesterol (decrease 6.7%), LDL cholesterol (decrease 6.3%) and plasma insulin concentrations (decrease 12%). The effects of modest changes in fasting serum triglycerides on CHD risk are unclear [27]. Long-term studies indicate that higher carbohydrate diets decrease risk for CHD events [80–82]. Of significance, the only diets that have been associated with documented regression of atherosclerosis are very low fat, high carbohydrate diets [49].

High fat diets increase postprandial hypertriglyceridemia and increase the concentration of atherogenic chylomicron remnants [83,84]. The postprandial triglyceride rise is related to the amount of fat in the meal, indicating that high fat meals are followed by significantly higher triglyceride concentrations than low fat meals [85]. These postprandial triglyceride-rich particles and remnant particles appear to be substantially more atherogenic than fasting VLDL particles [83]. During the weight loss phase, these risks may be smaller; however, if one continues these diets in a weight-maintaining state, the risk of accelerated atherosclerosis and atherosclerotic events may be substantially increased. When selecting diets for long-term use, one should consider the effects on risk for other CHD risk factors. Most experts in the weight management area suggest that high fat diets are associated with higher rates of weight gain than high carbohydrate diets [47,48], but this is still being debated [86]. Diets higher in animal fats appear significantly related to higher risks for coronary heart disease [70,71,87,88]. High fiber intakes, especially whole grains, appear to protect from CHD [50,64,89] and from developing diabetes [90,91].

Animal studies [92–94] and human studies [54,95] indicate that high-fat diets are associated with insulin resistance. Our studies [38–40] and others [54] indicate that high-carbohydrate, high-fiber, low-fat diets decrease insulin resistance. While authors of popular books claim that their high fat diets decrease insulin resistance, the only proven weight-maintaining dietary interventions for improved sensitivity to insulin are higher carbohydrate, higher fiber, lower fat diets [41,54]. High-fat, low-carbohydrate diets form the basis for the ketogenic diets advocated by Atkins and the Eadeses. These diets mobilize fatty acids from fat and produce proportional increases in serum ketone and free fatty acid concentrations [69,96]. Deprivation of dietary carbohydrate results in impaired glucose tolerance due to insulin resistance [97]. Reduction in dietary carbohydrate also increases postprandial free fatty acid concentrations in association with impaired glucose tolerance [98,99]. Our studies [100] indicate that high-carbohydrate, high-fiber, low-fat diets are accompanied by lower FFA values than low-carbohydrate, low-fiber, high-fat diets. Since FFA concentrations are a strong predictor of insulin sensitivity [101], higher FFA levels with high fat diets [69] would be associated with less insulin sensitivity than lower fat diets.

Many government agencies, expert advisory boards and disease panels have recommended higher carbohydrate, higher fiber, lower fat -especially saturated fat—diets in many Western countries [10–20]. There is a growing consensus around the recommendation for 6 to 11 servings of cereals—breads, breakfast cereals, rice, and pasta including three servings of whole grain foods—3 to 5 serving of vegetables and 2 to 4 servings of fruits per day. We have concerns about making alternative recommendations for overweight or obese individuals who already have increased risk for CHD, diabetes, hypertension and certain forms of cancer. Whole grains, fruits and vegetables are rich sources of fiber, antioxidants, phytoestrogens and other phytochemicals [50]. Generous intake of these foods is associated with a significant reduction in risk for CHD [50,102–104], cancer [50,103,105,106] and diabetes [50,90,91].

Finally, through the evolution of the ancestors of man, plant-based, high fiber, low animal fat diets were consumed. Stone tools and cooking methods sufficiently advanced to allow significant meat intake did not become available until the Paleolithic period. For 5 to 15 million years of the Miocene before the present time, consumption of high-fiber plant foods and exercise shaped the human genome. Such diets provide very little stimulus for cholesterol synthesis and greatly increase fecal bile acid losses compared to contemporary diets. The simian-like diets [107] demonstrate a 30% decrease in serum LDL-cholesterol concentrations similar to those predicted for the Ornish diet. The evolutionary argument therefore provides a further reason for favoring high-fiber, low-animal fat diets.

	CONCLUSIONS

TOP ABSTRACT INTRODUCTION METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
The Atkins and Protein Power diets are very high in total and saturated fat compared to current dietary guidelines. Long-term use of these diets for weight maintenance are likely to significantly increase serum cholesterol concentrations and risk for CHD. The Sugar Busters and Zone diets would lower serum cholesterol concentrations and likely reduce risk for CHD. Higher carbohydrate, higher fiber, lower fat diets would have the greatest effect in decreasing serum cholesterol concentrations and, thus, the risk for CHD. While high fat diets may promote short-term weight loss, the potential hazards for worsening risk for progression of atherosclerosis or atherosclerotic events override the short-term benefits.

	FOOTNOTES

 
Supported, in part, by Health Management Resources (HMR), HCF Nutrition Research Foundation, and the Natural Sciences and Engineering Research Council, Canada.

Received January 31, 2000. Accepted June 5, 2000.

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