Unformatted text preview: ORIGINAL CONTRIBUTION Comparison of the Atkins, Zone, Ornish, and LEARN Diets for Change in Weight and Related Risk Factors Among Overweight Premenopausal Women
The A TO Z Weight Loss Study: A Randomized Trial
Christopher D. Gardner, PhD Alexandre Kiazand, MD Sofiya Alhassan, PhD Soowon Kim, PhD Randall S. Stafford, MD, PhD Raymond R. Balise, PhD Helena C. Kraemer, PhD Abby C. King, PhD
HE ONGOING OBESITY EPI demic,1 along with its health costs and consequences2 and the health benefits of weight loss,3-6 have been well established. National dietary weight loss guidelines (ie, energy-restricted, low in fat, high in carbohydrate)7 have been challenged, particularly by proponents of lowcarbohydrate diets.8,9 However, limited evidence has been available to effectively evaluate other diets.10,11 Several recent trials compared lowcarbohydrate vs traditional low-fat, high-carbohydrate weight-loss diets.12-16 A meta-analysis that pooled the results of these early trials concluded that low-carbohydrate, non– energy-restricted diets were at least as effective as low-fat, high-carbohydrate diets in inducing weight loss for up to 1 year.17 However, most of these trials were limited by combinations of small sample sizes, high rates of attrition, short durations, or limited diet assessment. For the A TO Z (Atkins, Traditional, Ornish, Zone) Weight Loss Study, we Context Popular diets, particularly those low in carbohydrates, have challenged current recommendations advising a low-fat, high-carbohydrate diet for weight loss. Potential benefits and risks have not been tested adequately. Objective To compare 4 weight-loss diets representing a spectrum of low to high carbohydrate intake for effects on weight loss and related metabolic variables. Design, Setting, and Participants Twelve-month randomized trial conducted in the United States from February 2003 to October 2005 among 311 free-living, overweight/obese (body mass index, 27-40) nondiabetic, premenopausal women. Intervention Participants were randomly assigned to follow the Atkins (n=77), Zone (n = 79), LEARN (n=79), or Ornish (n=76) diets and received weekly instruction for 2 months, then an additional 10-month follow-up. Main Outcome Measures Weight loss at 12 months was the primary outcome. Secondary outcomes included lipid profile (low-density lipoprotein, high-density lipoprotein, and non–high-density lipoprotein cholesterol, and triglyceride levels), percentage of body fat, waist-hip ratio, fasting insulin and glucose levels, and blood pressure. Outcomes were assessed at months 0, 2, 6, and 12. The Tukey studentized range test was used to adjust for multiple testing. Results Weight loss was greater for women in the Atkins diet group compared with the other diet groups at 12 months, and mean 12-month weight loss was significantly different between the Atkins and Zone diets (P .05). Mean 12-month weight loss was as follows: Atkins, −4.7 kg (95% confidence interval [CI], −6.3 to −3.1 kg), Zone, −1.6 kg (95% CI, −2.8 to −0.4 kg), LEARN, −2.6 kg (−3.8 to −1.3 kg), and Ornish, −2.2 kg (−3.6 to −0.8 kg). Weight loss was not statistically different among the Zone, LEARN, and Ornish groups. At 12 months, secondary outcomes for the Atkins group were comparable with or more favorable than the other diet groups. Conclusions In this study, premenopausal overweight and obese women assigned to follow the Atkins diet, which had the lowest carbohydrate intake, lost more weight and experienced more favorable overall metabolic effects at 12 months than women assigned to follow the Zone, Ornish, or LEARN diets. While questions remain about long-term effects and mechanisms, a low-carbohydrate, high-protein, high-fat diet may be considered a feasible alternative recommendation for weight loss. Trial Registration clinicaltrials.gov Identifier: NCT00079573
JAMA. 2007;297:969-977 www.jama.com Author Affiliations: Stanford Prevention Research Center and the Department of Medicine, Stanford University Medical School, Stanford, Calif. Corresponding Author: Christopher D. Gardner, PhD, Hoover Pavilion, N229, 211 Quarry Rd, Stanford, CA 94305-5705 ([email protected] .edu). 969 T selected 4 diets—3 popular and substantially different diets and 1 diet based on national guidelines—representing a spectrum of carbohydrate intake: Atkins8 (very low in carbohydrate), Zone9 ©2007 American Medical Association. All rights reserved. (Reprinted) JAMA, March 7, 2007—Vol 297, No. 9 Downloaded from www.jama.com at Univ of California -Davis, on March 6, 2007 ONE-YEAR EFFECT OF WEIGHT-LOSS DIETS (low in carbohydrate), LEARN18 (Lifestyle, Exercise, Attitudes, Relationships, and Nutrition; low in fat, high in carbohydrate, based on national guidelines), and Ornish19 (very high in carbohydrate). The primary study objective was to examine the effects of diets and gradations of carbohydrate intake on weight loss and related metabolic variables in overweight and obese premenopausal women. METHODS
Participants Participants were recruited from the local community, primarily through media advertisements. Premenopausal women aged 25 to 50 years were invited to enroll if their body mass index (calculated as weight in kilograms divided by height in meters squared) was 27 to 40, body weight was stable over the previous 2 months, and medications were stable for at least 3 months. Women were excluded if they self-reported hypertension (except for those whose blood pressure was stable using antihypertension medications); type 1 or 2 diabetes mellitus; heart, renal, or liver disease; cancer or active neoplasms; hyperthyroidism unless treated and under control; any medication use known to affect weight/energy expenditure; alcohol intake of at least 3 drinks/d; or pregnancy, lactation, no menstrual period in the previous 12 months, or plans to become pregnant within the next year. Race/ethnicity data were collected by self-report to be used for descriptive purposes and possible ancillary analyses of subgroups. All study participants provided written informed consent. The study was approved annually by the Stanford University Human Subjects Committee.
Intervention Participants were enrolled in 4 cohorts, with the first cohort starting in February 2003 and the last cohort starting in September 2004. Randomization was conducted in blocks of 24 (6 per treatment group) and occurred by having a blinded research technician select folded pieces of paper with group assignments from an opaque enve- lope. Participants were assigned 1 of 4 diet books: Dr Atkins’ New Diet Revolution,8 Enter the Zone,9 The LEARN Manual for Weight Management,18 or Eat More, Weigh Less by Ornish.19 Each diet group attended 1-hour classes led by a registered dietitian once per week for 8 weeks and covered approximately one eighth of their respective books per class. The same dietitian taught all classes to all groups in all 4 cohorts and was rated by participants at the end of the 8-week sessions for enthusiasm and knowledge of the material (rating scale of 1-5, from “strongly disagree” to “strongly agree,” respectively). The LEARN program is intended to be a 16-week program and, therefore, the 8 weeks of guidance through this book reflected an accelerated time frame, which was necessary to match the time frame given for the other 3 diet groups. Efforts to maximize retention in the study included e-mail and telephone reminders for appointments, e-mail or telephone contact from staff between the 2- and 6-month and between the 6- and 12month data collection points, and incentive payments of $25, $50, and $75 for completing the 2-, 6-, and 12month data collection, respectively. Each group received specific target goals according to the emphasis of the assigned diet. The Atkins group aimed for 20 g/d or less of carbohydrate for “induction” (usually 2-3 months) and 50 g/d or less of carbohydrate for the subsequent “ongoing weight loss” phase. The Zone group’s primary emphasis was a 40%-30%-30% distribution of carbohydrate, protein, and fat, respectively. The LEARN group was instructed to follow a prudent diet that included 55% to 60% energy from carbohydrate and less than 10% energy from saturated fat, caloric restriction, increased exercise, and behavior modification strategies. The primary emphasis for the Ornish group was no more than 10% of energy from fat. Additional recommendations given for physical activity, nutritional supplements, and behavioral strategies were consistent with those presented in each diet book.8,9,18,19 The guidelines for the Zone and LEARN diets incorporated specific goals for energy restriction, while for the Atkins and Ornish diets, there were no specific energy restriction goals. A range of behavior modification techniques were discussed during the 2-month classes. The Ornish and Zone books suggest some stimulus-control strategies but on the whole do not emphasize behavior modification, whereas both the Atkins and LEARN books suggest multiple strategies, such as relapse preparation and planning strategies and goal setting. Overall, the LEARN manual has the greatest emphasis on behavior modification strategies.
Process and Outcome Measures All data were collected at baseline, 2, 6, and 12 months. Diet and Physical Activity Data. Dietary intake data were collected by telephone-administered, 3-day, unannounced, 24-hour dietary recalls using Nutrition Data System for Research software, versions 4.05.33, 4.06.34, and 5.0.35 (Nutrition Coordinating Center, University of Minnesota, Minneapolis). Data collectors were trained and certified by the Nutrition Coordinating Center. The recalls occurred on 2 weekdays and 1 weekend day per time point, on nonconsecutive days whenever possible. Local foods not found in the comprehensive database were added to the database manually. A “food amounts booklet” was used to assist participants with portion size estimation. Energy expenditure was assessed using the well-established Stanford 7-day physical activity recall.20 Anthropometric Data. Height was measured to the nearest millimeter using a standard wall-mounted stadiometer. Body weight was measured to the nearest 0.1 kg on a calibrated clinical scale. Waist and hip circumference were measured to the nearest millimeter by standard procedures using a 150-cm anthropometric measuring tape.21 Whole-body fat (percentage of body mass) was determined by dualenergy x-ray absorptiometry using pencil-beam mode on the Hologic QDR2000 (first 3 cohorts) and, later, the 970 JAMA, March 7, 2007—Vol 297, No. 9 (Reprinted) ©2007 American Medical Association. All rights reserved. Downloaded from www.jama.com at Univ of California -Davis, on March 6, 2007 ONE-YEAR EFFECT OF WEIGHT-LOSS DIETS array mode on a Hologic QDR 4500 densitometer (last cohort) (Hologic Inc, Waltham, Mass). Metabolic Measures. Blood samples were collected after a 10-hour or longer fast. Plasma total cholesterol and triglycerides (free glycerol blank subtracted) were measured enzymatically using Stanford Clinical Chemistry Laboratory– established methods.22,23 High-density lipoprotein cholesterol (HDL-C) was measured by liquid selective detergent followed by enzymatic determination of cholesterol.24 Low-density lipoprotein cholesterol (LDL-C) was calculated according to the methods described by Friedewald et al.25 Lipid assays were monitored by the Lipid Standardization Program of the Centers for Disease Control and Prevention and were consistently within specified limits (monthly coefficients of variation were all 3.1%). The non–HDL-C measure was defined as total cholesterol value minus HDL-C value.26 Total plasma insulin in serum was measured by radioimmunoassay.27 Blood glucose was measured using a modification of the glucose oxidase/ peroxidase method.28,29 Resting blood pressure was measured 3 times at 2-minute intervals as described elsewhere30; the initial reading was discarded and the last 2 readings were averaged. Clinic and laboratory staff members were blinded to treatment assignment.
Statistical Analyses to detect a 2.7-kg difference for 12month weight change between groups. Dietary composition data (energy intake; percentage carbohydrate, fat, and protein; and grams of saturated fat and fiber) were analyzed using raw, unadjusted means (SDs) (ie, no imputation for missing data). Between-group differences in dietary intake at each time point were tested by analysis of variance (ANOVA). For weight and for all secondary outcome measures, analyses were conducted using all time points and all diets and were tested for diet group time (log time 1) interactions in a mixed model using autoregressive covariance structure (SAS version 9.1.3 with Service Pack 3, SAS Institute Inc, Cary, NC). Triglyceride data were log-transformed to attain normal distributions for testing; for ease of interpretation, values presented in the text and figures are untransformed. Differences among diets for 12month changes from baseline were tested by ANOVA. For statistically sigFigure 1. Participant Flow Through the Trial nificant ANOVAs, all pairwise comparisons among the 4 diets were tested using the Tukey studentized range adjustment. Statistical testing of changes from baseline to 2 months and to 6 months using pairwise comparisons are presented for descriptive purposes. For exploratory purposes, ancillary analyses were conducted to determine the effect of diet group assignment on secondary outcomes at 12 months after adjusting for changes in weight loss using linear regression. Also for exploratory purposes, all analyses of weight and secondary outcome measures were tested using only available data, without using baseline values carried forward for missing data or other imputation methods. There were no substantive differences in any of these findings compared with the analyses with baseline values carried forward and, therefore, only the primary analyses are presented. Multiple regression was used to examine potential interactions between race/ethnicity and diet 1479 Individuals Screened 698 Ineligible or Not Interested 362 BMI Too Low 86 BMI Too High 103 Scheduling Problems 86 Medications/Medical Reasons 61 Dietary Issues 470 Declined to Participate or Other 311 Randomized The primary objective was to test whether any of the 4 diets, representing a spectrum of carbohydrate intake, was more effective than any other in 12-month weight loss. The selected minimal clinically significant betweengroup difference in weight change was 2.7 kg (6 lb, approximately 3% for a 180-lb individual). Based on previous trials, we projected a 6.3-kg SD of weight change.31,32 The primary analysis was conducted applying intentionto-treat methods with baseline values carried forward for missing values. Thus, with 4 treatment groups and a projected 75 participants per group, the study was designed to have 80% power 77 Assigned to Atkins Diet Group Withdrawals Prior to Data Collection 5 at 2 mo 1 at 6 mo 3 at 12 mo 9 Withdrew 1 Schedule 1 Pregnant 1 Personal/Family 0 Moved 2 Health 1 Did Not Enjoy 3 Other 68 Completed Protocol 77 Included in Primary Analysis 79 Assigned to Zone Diet Group Withdrawals Prior to Data Collection 7 at 2 mo 6 at 6 mo 5 at 12 mo 18 Withdrew 9 Schedule 2 Pregnant 2 Personal/Family 2 Moved 0 Health 0 Did Not Enjoy 3 Other 61 Completed Protocol 79 Included in Primary Analysis 79 Assigned to LEARN Diet Group Withdrawals Prior to Data Collection 7 at 2 mo 9 at 6 mo 2 at 12 mo 18 Withdrew 5 Schedule 3 Pregnant 2 Personal/Family 2 Moved 1 Health 1 Did Not Enjoy 4 Other 61 Completed Protocol 79 Included in Primary Analysis 76 Assigned to Ornish Diet Group Withdrawals Prior to Data Collection 5 at 2 mo 6 at 6 mo 6 at 12 mo 17 Withdrew 6 Schedule 1 Pregnant 1 Personal/Family 0 Moved 0 Health 1 Did Not Enjoy 8 Other 59 Completed Protocol 76 Included in Primary Analysis ©2007 American Medical Association. All rights reserved. (Reprinted) JAMA, March 7, 2007—Vol 297, No. 9 971 Downloaded from www.jama.com at Univ of California -Davis, on March 6, 2007 ONE-YEAR EFFECT OF WEIGHT-LOSS DIETS group for effects on weight loss; there were no significant interactions. All statistical tests were 2-tailed using a significance level of .05. RESULTS Participant enrollment began in February 2003, and the study ended in October 2005. FIGURE 1 shows participant flow; T ABLE 1 shows baseline characteristics. In all 4 diet groups, 85% to 89% of participants attended at least 75% of their assigned classes ( 6 of 8). Attendance was not different by diet group ( P = .68). Retention at 12 months was 88%, 77%, 76%, and 78% for the Atkins, Zone, LEARN, and Ornish groups, respectively, and was
Table 1. Baseline Participant Characteristics*
Characteristics Demographics Age, y Education, y Race/ethnicity, No. (%) White Black Hispanic Asian/Pacific Islander Other Smokers, No. (%) Physical activity, kcal/kg per d Anthropometrics Weight, kg Body fat, % Body mass index† Waist-hip ratio Cardiovascular disease risk factors LDL-C, mg/dL HDL-C, mg/dL Triglycerides, mg/dL Non–HDL-C, mg/dL Ratio of total cholesterol to HDL-C Fasting insulin, µU/mL Fasting glucose, mg/dL Blood pressure, mm Hg Systolic Diastolic Metabolic syndrome, No. (%)‡ Atkins (n = 77) 42 (5) 16 (2) 59 (76) 2 (3) 7 (9) 7 (9) 2 (3) 2 (3) 34 (6) 86 (13) 41 (6) 32 (4) 0.843 (0.067) 109 (29) 53 (14) 125 (78) 134 (33) 3.7 (1.0) 10 (7) 92 (9) 118 (11) 75 (8) 22 (29) not significantly different among groups (P = .30). Participant ratings for class instructor enthusiasm and knowledge of material were very high for both among all diet groups and were not significantly different among groups; average scores ranged from 4.4 to 4.7 on a scale of 1 to 5, with 5 as the highest rating.
Dietary Intake and Energy Expenditure Total energy intake was not different among diet groups at baseline or any subsequent time point ( P . 40 for all) (TABLE 2). However, relative to baseline, there was a significant mean decrease in reported energy intake at all postrandomization time points Zone (n = 79) 40 (6) 16 (2) 52 (66) 7 (9) 8 (10) 9 (11) 3 (4) 4 (5) 34 (6) 84 (12) 40 (6) 31 (3) 0.841 (0.068) 114 (32) 52 (11) 123 (98) 139 (39) 3.8 (1.1) 10 (7) 94 (20) 115 (13) 74 (9) 20 (25) LEARN (n = 79) 40 (7) 16 (2) 59 (75) 6 (7) 7 (9) 6 (8) 1 (1) 4 (5) 34 (5) 85 (14) 38 (6) 31 (4) 0.839 (0.066) 104 (29) 51 (11) 119 (73) 127 (34) 3.6 (1.0) 10 (8) 96 (17) 116 (12) 75 (9) 29 (37) Ornish (n = 76) 42 (6) 16 (2) 52 (69) 4 (5) 11 (14) 8 (10) 1 (1) 3 (4) 35 (7) 86 (10) 40 (6) 32 (3) 0.840 (0.060) 111 (27) 50 (11) 118 (62) 135 (33) 3.8 (1.0) 10 (5) 93 (13) 116 (10) 75 (8) 27 (36) All Diets (n = 311) 41 (6) 16 (2) 71 6 11 10 2 4 34 (6) 85 (12) 40 (6) 32 (4) 0.841 (0.065) 110 (29) 52 (12) 121 (78) 134 (35) 3.7 (1.0) 10 (6) 94 (15) 116 (11) 75 (8) 99 (32) (P .001): −497 (SD, 496), −387 (SD, 498), and −351 (SD, 576) kcal/d at 2, 6, and 12 months, respectively, for all groups combined. There were no significant group differences at baseline in percentage of energy from carbohydrate, fat, or protein or in grams of saturated fat or fiber, except for a borderline significant difference in percentage of energy from fat between Atkins and LEARN (P = .05) (Table 2). At subsequent time points the diets were statistically different in carbohydrate content, progressing from low to high across the Atkins, Zone, LEARN, and Ornish groups. This same pattern was observed for fiber intake. The reverse pattern, higher to lower intakes, was statistically significant for protein, fat, and saturated fat at all time points. Between-group differences in patterns of nutrient intake were largest at 2 months. At 12 months, the patterns of nutrient differences between groups were still present, but the magnitude of differences was diminished. Total energy expenditure was slightly higher for the Ornish group vs the other 3 groups at baseline but was not significantly different among groups at any subsequent time point (Table 1). Relative to baseline, there was a modest and significant mean increase (P .05) in energy expenditure at all time points for all groups combined: 0.5 (SD, 2.8), 0.4 (SD, 2.7), and 1.0 (SD, 3.0) kcal/kg per day at 2, 6, and 12 months, respectively.
Weight and Anthropometric Outcomes Abbreviations: HDL-C, high-density lipoprotein cholesterol; LDL-C, low-density lipoprotein cholesterol. SI conversions: To convert LDL-C, HDL-C, and total cholesterol to mmol/L, multiply by 0.0259. To convert triglycerides to mmol/L, multiply by 0.0113. To convert glucose to mmol/L, multiply by 0.0555. *Data are expressed as mean (SD) unless otherwise indicated. †Calculated as weight in kilograms divided by height in meters squared. ‡Determined by criteria of ATP III.33 Mean 12-month weight change was −4.7 kg (95% confidence interval [CI], −6.3 to −3.1 kg) for Atkins, −1.6 kg (95% CI, −2.8 to −0.4 kg) for Zone, −2.2 kg (95% CI, −3.6 to −0.8 kg) for LEARN, and −2.6 kg (95% CI, −3.8 to −1.3 kg) for Ornish and was significantly different for Atkins vs Zone (FIGURE 2). At the 2- and 6-month intermediate time points, the weight change for the Atkins group was significantly greater than for all other groups (P .05). Weight change among 972 JAMA, March 7, 2007—Vol 297, No. 9 (Reprinted) ©2007 American Medical Association. All rights reserved. Downloaded from www.jama.com at Univ of California -Davis, on March 6, 2007 ONE-YEAR EFFECT OF WEIGHT-LOSS DIETS the Zone, LEARN, and Ornish groups did not differ significantly at any time point. The pattern of changes in body mass index, percentage of body fat, and waist-hip ratio among groups paralleled the changes in weight, although the between-group differences at 12 months did not achieve statistical significance for percentage of body fat ( P = .07) or waist-hip ratio (P = .10) (TABLE 3).
Lipid Outcomes favored the Atkins over the Ornish group.
Ancillary Analyses of Diet Group Effects Independent of Changes in Weight For the 249 participants who completed the full 12-month protocol, we examined the independent effect of diet group on secondary outcomes after adjusting for 12-month changes in weight using linear regression. Each of the sta- tistically significant 12-month differences between diet groups (ie, triglycerides, HDL-C, and systolic and diastolic blood pressure; Table 3) remained statistically significant after including weight loss in the model; however, the level of significance was diminished. COMMENT Compared with women who were assigned to follow diets having higher car- Results generated by 84% of the study population (n = 262) with baseline blood samples (Atkins, n = 70; Zone, n = 65; LEARN, n = 63; and Ornish, n=64) were available for testing. Four of the LDL-C values could not be calculated because of triglyceride concentrations greater than 400 mg/dL (4.52 mmol/L) and were treated as missing data. At all time points, the statistically significant findings for HDL-C and triglycerides concentrations favored the Atkins group (Table 3). Changes in LDL-C concentrations at 2 months favored the LEARN and Ornish diets over the Atkins diet; however, these differences diminished and were no longer significant at 6 and 12 months. NonHDL-C differences among groups were not significant at any time point.
Insulin, Glucose, and Blood Pressure Outcomes Table 2. Mean Dietary Intake and Energy Expenditure by Diet Group and Time Point*
Atkins Energy, kcal/d Baseline 2 mo 6 mo 12 mo Carbohydrate (% energy) Baseline 2 mo 6 mo 12 mo Protein (% energy) Baseline 2 mo 6 mo 12 mo Fat (% energy) Baseline 2 mo 6 mo 12 mo Saturated fat, g/d Baseline 2 mo 6 mo 12 mo Fiber, g/d Baseline 2 mo 6 mo 12 mo Energy expenditure, kcal/kg per d Baseline 2 mo 6 mo 12 mo 1888 (512) 1381 (345) 1538 (401) 1599 (494) 45.6 (10.5) 17.7 (11.8)a 29.5 (14.5)a 34.5 (14.4)a 16.6 (4.1) 27.7 (5.5)a 22.4 (6.3)a 20.6 (5.3)a 36.2 (7.8)a 54.7 (9.0)a 47.0 (11.9)a 44.3 (12.5)a 26.5 (11.1) 30.7 (9.8)a 28.1 (11.1)a 27.2 (13.3)a 17.4 (6.6) 11.0 (6.3)a 14.0 (6.3)a 15.2 (6.6)a 33.7 (1.8)a 34.6 (2.1) 34.3 (2.4) 34.8 (2.7) Zone 1975 (567) 1455 (464) 1503 (348) 1594 (523) 47.1 (9.0) 42.0 (8.5)b 43.7 (9.2)b 45.4 (11.1)b 15.6 (3.3) 23.7 (5.8)b 20.1 (5.2)a,b 20.0 (5.2)a,b 35.6 (6.5)a,b 34.8 (6.6)b 35.7 (7.3)b 34.5 (7.8)b 27.0 (10.9) 19.3 (10.3)b 20.5 (8.0)b 21.6 (11.2)b 17.8 (8.7) 16.9 (6.7)b 15.3 (7.6)a 16.7 (9.4)a,b 34.1 (2.6)a 34.5 (2.4) 34.4 (1.9) 35.4 (3.3) LEARN 1925 (553) 1476 (448) 1598 (418) 1654 (492) 48.3 (9.2) 49.3 (8.6)c 48.2 (8.6)b,c 47.2 (8.9)b,c 16.7 (3.9) 20.1 (4.8)c 18.4 (4.6)b 18.5 (4.6)a,b 33.2 (7.2)b 30.2 (7.3)c 31.3 (7.8)c 32.9 (7.1)b 24.3 (11.0) 16.8 (9.8)b 19.0 (8.9)b,c 20.1 (9.8)b 17.6 (7.5) 17.8 (7.1)b 16.7 (6.3)a,b 18.3 (7.8)a,b 33.9 (1.5)a 34.8 (2.4) 34.8 (2.0) 35.6 (2.2) Ornish 1850 (541) 1408 (453) 1553 (530) 1505 (437) 47.9 (8.6) 63.1 (11.0)d 53.4 (13.4)c 52.4 (12.3)c 16.3 (3.1) 16.9 (4.3)d 18.1 (4.8)b 18.3 (4.0)b 35.1 (7.0)a,b 21.1 (8.0)d 28.3 (10.7)c 29.8 (10.5)b 24.8 (10.3) 10.3 (7.8)c 16.2 (10.1)c 16.9 (11.4)b 16.6 (6.6) 22.1 (9.4)c 19.3 (11.1)b 19.3 (9.4)b 34.9 (3.2)b 34.7 (2.3) 34.6 (2.3) 35.8 (5.8) P Value† .52 .52 .64 .43 .31 .001 .001 .001 .21 .001 .001 .02 .05 .001 .001 .001 .34 .001 .001 .001 .79 .001 .001 .03 .007 .88 .65 .42 Insulin and glucose measurements were obtained from the same aforementioned 84% of the total sample for lipids. Neither the overall trajectory (ie, across all time points) nor the 12month differences were significantly different among groups for either fasting insulin or fasting glucose concentrations (Table 3). Parallel to the group changes in weight, the decrease in mean blood pressure levels was largest in the Atkins group at all time points. At 12 months, the decrease in systolic blood pressure was significantly greater for the Atkins group than for any other group. For diastolic pressure, the only significant pairwise difference at 12 months *Data presented are unadjusted raw data with no imputations for missing data. Standard deviations are presented in parentheses. Sample sizes for baseline and 2, 6, and 12 months, respectively, are: Atkins, n = 77, 73, 71, and 68; Zone, n = 79, 73, 67, and 57; LEARN, n = 79, 73, 66, and 60; and Ornish, n = 76, 72, 67, and 56. †By analysis of variance. a,b,c,d When the analysis of variance (last column) was statistically significant (P .05), all pairwise comparisons among diet groups were tested for statistical significance using the Tukey studentized range test. Pairwise comparisons that were significantly different from one another are indicated by superscripts as follows: when the values for 2 diet groups within a row do not share a common superscript, they are significantly different, whereas if the values do share a common superscript, they are not significantly different. ©2007 American Medical Association. All rights reserved. (Reprinted) JAMA, March 7, 2007—Vol 297, No. 9 973 Downloaded from www.jama.com at Univ of California -Davis, on March 6, 2007 ONE-YEAR EFFECT OF WEIGHT-LOSS DIETS Figure 2. Weight Change Relative to Baseline
Zone 0 LEARN Ornish Atkins –1 –2 –3 –4 –5 –6 –7 Baseline 2 6 12 Time, mo Baseline values were carried forward for any missing values. The overall diet group time interaction was significant (P .001). The analysis of variance test for differences among diet groups in weight change from baseline was significant at 2 and 6 months (P .001), and at 12 months (P = .01). Analyses of all pairwise differences by the Tukey standardized range test ( .05) indicate that the Atkins diet group was significantly different than all other diet groups at 2 and 6 months and that the Atkins diet group was significantly different than the Zone diet group at 12 months. There were no significant differences among the Zone, LEARN, or Ornish diet groups at any time point. Error bars indicate standard error of the mean. bohydrate content, women assigned to the diet with the lowest carbohydrate content had more weight loss and more favorable changes in related metabolic risk factors at 2 and 6 months. The finding of greater weight loss for the Atkins diet continued through 12 months, reaching statistical significance in comparison with the Zone diet. There were no significant differences in weight loss at any time point among the Zone, LEARN, and Ornish diets. Although the weight loss in the Atkins group was greater than that of other groups, the magnitude of weight loss was modest, with a mean 12-month weight loss of only 4.7 kg. Many concerns have been expressed that low-carbohydrate weightloss diets, high in total and saturated fat, will adversely affect blood lipid levels and cardiovascular risk.34-36 These concerns have not been substantiated in recent weight-loss diet trials. The recent trials, like the current study, have consistently reported that triglycerides, HDL-C, blood pressure, and measures of insulin resistance either were not significantly different or were more favorable for the very-low-carbohydrate groups.12-16 The exception to this pattern has been LDL-C concentrations. Two of the most consistent findings in recent trials of low-carbohydrate vs low-fat diets have been higher LDL-C concentrations and lower triglyceride concentrations in the low-carbohydrate diets.17 Although a higher LDL-C concentration would appear to be an adverse effect, this may not be the case under these study conditions. The triglyceridelowering effect of a low-carbohydrate diet leads to an increase in LDL particle size, which is known to decrease LDL atherogenicity.37-39 In the current study, at 2 months, mean LDL-C concentrations increased by 2% and mean triglyceride concentrations decreased by 30% in the Atkins group. These findings are consistent with a beneficial increase in LDL particle size, although LDL particle size was not assessed in our study. In addition, we examined non–HDL-C concentrations as an alternate indicator of atherogenic lipoproteins—a variable not substantially influenced by changes in triglyceride concentrations26—and observed no significant differences among groups at any time point. Therefore, we interpret these findings to suggest that there were no adverse effects on the lipid variables for women following the Atkins diet compared with the other diets and, furthermore, no adverse effects were observed on any weight-related variable measured in this study at any time point for the Atkins group. Further examination of the dietary effects on lipid variables would benefit from analyses of lipoprotein particle subfractions and follow-up of longer than 12 months. Our study and the study by Dansinger et al16 were similar in several design features, including similar number and types of treatment groups and the same duration. Despite the similarities in design, several conclusions differed between the trials. Dansinger et al reported that weight loss at 12 months did not differ by diet group but only by level of adherence, regardless of diet type. In addition, Dansinger et al reported improvements within groups over 12 months for cardiac risk factors but did not report any significant differences between groups. In contrast, we observed statistically significant differences among diet groups for both weight loss and risk factors at 12 months. These differences are likely attributable to at least 2 factors. One factor concerns the different study populations: our study was restricted to women aged 20 to 50 years who did not have diabetes and were not taking medications for cardiac risk factors, whereas the population in the study by Dansinger et al was much broader in its inclusion criteria. A second likely factor was differences in statistical power; in the study by Dansinger et al, 93 of 160 enrolled participants completed the trial (42% attrition at 12 months; ie, n=21-26 per treatment group); in the current study, 248 of 311 women completed the trial (20% attrition; ie, n=58-68 per treatment group). The current study examined whether risk factor responses to diets were independent of weight loss. After statistically adjusting for weight loss differentials among groups, the secondary outcome differences among groups at 12 months that were significant in the unadjusted model remained significant in the adjusted model, although the level of significance was diminished. This supports a combined effect of benefit for the very-low-carbohydrate Atkins diet attributable to both increased weight loss and dietary composition. However, our study was not designed to specifically address this ancillary question. Krauss et al38 recently addressed this issue directly in a study testing diets that ranged from low to high carbohydrate intake under conditions of weight stability followed by conditions of weight loss. Improvements in lipids and lipoproteins were greater for participants in the verylow-carbohydrate diet during the weight-stable phase but were greater for those in the high-carbohydrate diet Mean Weight Change, kg 974 JAMA, March 7, 2007—Vol 297, No. 9 (Reprinted) ©2007 American Medical Association. All rights reserved. Downloaded from www.jama.com at Univ of California -Davis, on March 6, 2007 ONE-YEAR EFFECT OF WEIGHT-LOSS DIETS Table 3. Mean Changes in Secondary Outcomes Relative to Baseline, by Diet Group and Time*
P Value Atkins (n = 77) Body mass index§ 2 mo 6 mo 12 mo Body fat, % 2 mo 6 mo 12 mo Waist-hip ratio 2 mo 6 mo 12 mo LDL-C, mg/dL 2 mo 6 mo 12 mo HDL-C, mg/dL 2 mo 6 mo 12 mo Triglycerides, mg/dL 2 mo 6 mo 12 mo Non–HDL-C, mg/dL 2 mo 6 mo 12 mo Insulin, µU/mL 2 mo 6 mo 12 mo Glucose, mg/dL 2 mo 6 mo 12 mo Systolic blood pressure, mm Hg 2 mo 6 mo 12 mo Diastolic blood pressure, mm Hg 2 mo 6 mo 12 mo –1.60 (0.98) –2.16 (2.14) –1.65 (2.54)a −2.1 (1.8) −3.6 (4.1) −2.9 (4.8) −0.019 (0.016) −0.021 (0.023) −0.019 (0.026) 2.3 (23.5) 1.7 (22.3) 0.8 (22.6) –0.4 (7.7) 5.1 (9.6) 4.9 (9.1)a –52.3 (66.8) –35.6 (64.4) –29.3 (59.0)a –8.0 (26.3) –4.7 (23.1) –5.1 (22.5) −3.0 (3.9) −2.8 (4.1) −1.8 (4.8) −0.4 (6.8) 0.2 (7.6) −1.8 (13.4) −6.8 (8.0) −6.4 (9.5) –7.6 (11.0)a −2.9 (6.2) −3.3 (6.9) –4.4 (8.4)a Zone (n = 79) –0.76 (0.99) –0.73 (0.90) –0.53 (2.00)b −1.8 (2.0) −1.7 (3.1) −1.3 (3.4) −0.012 (0.019) −0.014 (0.023) −0.013 (0.023) –5.3 (17.8) 0.5 (14.9) 0.0 (17.6) –0.5 (5.4) 3.3 (6.9) 2.2 (6.1)a,b –24.8 (53.1) –21.3 (58.9) –4.2 (48.5)b –10.2 (21.7) –3.7 (18.8) –0.5 (20.0) 1.0 (6.0) 0.1 (8.9) −1.5 (4.9) −1.6 (10.6) −1.7 (9.6) −1.6 (6.5) −3.2 (8.2) −3.6 (8.0) –3.3 (8.1)b −2.1 (5.6) −1.8 (5.6) –2.1 (5.8)a,b LEARN (n = 79) –0.99 (1.00) –1.13 (1.91) –0.92 (2.00)a,b −1.5 (1.8) −2.0 (3.2) −1.0 (3.4) −0.012 (0.022) −0.010 (0.022) −0.009 (0.024) –7.3 (20.8) –2.4 (19.4) 0.6 (17.0) –3.8 (6.1) 2.1 (6.7) 2.8 (7.7)a,b –17.4 (48.9) –16.1 (50.1) –14.6 (60.8)a,b –10.7 (19.0) –5.6 (18.6) –4.0 (19.7) −1.9 (4.7) −2.1 (5.4) −1.8 (5.1) −0.8 (8.3) −0.9 (9.9) 0.5 (9.2) −3.6 (6.9) −4.3 (7.6) –3.1 (9.3)b −1.4 (4.4) −2.5 (5.8) –2.2 (6.7)a,b Ornish (n = 76) –0.95 (0.90) –0.85 (1.60) –0.77 (2.14)a,b .01 −1.2 (1.5) −1.4 (2.7) −1.5 (4.0) .04 −0.009 (0.019) −0.010 (0.023) −0.012 (0.024) .26 –10.1 (19.8) –3.2 (19.9) –3.8 (19.0) .03 –5.3 (9.0) 0.0 (9.2) 0.0 (6.3)b .003 10.9 (55.0) –7.6 (54.4) –14.9 (46.2)a,b .92 –7.8 (17.8) –4.7 (22.1) –6.8 (20.3) .23 −1.1 (3.3) −0.1 (3.6) −0.2 (3.8) .77 −1.4 (6.9) −0.6 (7.3) −0.8 (7.9) .001 −1.6 (6.3) −1.7 (7.0) –1.9 (7.7)b .03 −0.4 (5.5) −1.0 (5.6) –0.7 (6.0)b Overall Diet Group Time† .001 12 Months‡ .01 .07 .10 .49 .002 .01 0.36 .17 .54 .001 .009 SI conversions: To convert LDL-C, HDL-C, and total cholesterol to mmol/L, multiply by 0.0259. To convert triglycerides to mmol/L, multiply by 0.0113. To convert glucose to mmol/L, multiply by 0.0555. *Intention-to-treat analysis, with baseline data carried forward for missing values. Standard deviations are presented in parentheses. For LDL-C, HDL-C, triglyceride, non−HDL-C, insulin, and glucose data, results are presented for those with available blood sample data (84% of full sample): Atkins, n = 70; Zone, n = 65; LEARN, n = 63; and Ornish, n = 64. †P value for diet group time interaction, determined using mixed-model and autoregressive covariance structure. ‡P values for 12-month change from baseline results, determined by analysis of variance. §Calculated as weight in kilograms divided by height in meters squared. a,b For a given outcome measure at the 12-month time point, when the analysis of variance (last column) was statistically significant (P .05), all pairwise comparisons among diet groups were tested for statistical significance using the Tukey studentized range test. Pairwise comparisons that were significantly different from one another are indicated by superscripts as follows: when the values for 2 diet groups within a row do not share a common superscript, they are significantly different, whereas if the values do share a common superscript, they are not significantly different. ©2007 American Medical Association. All rights reserved. (Reprinted) JAMA, March 7, 2007—Vol 297, No. 9 975 Downloaded from www.jama.com at Univ of California -Davis, on March 6, 2007 ONE-YEAR EFFECT OF WEIGHT-LOSS DIETS after weight loss and restabilization; overall the low-carbohydrate and weight-loss effects were reported to be equivalent but not additive under the tightly controlled conditions of this study. The 4 study diets used in our study differed significantly in composition beyond carbohydrate content. Protein, fat, and saturated fat followed a continuum across diets, inverse to carbohydrate content. In a series of recent weight-loss trials that substituted either protein for fat while holding carbohydrate constant40,41 or protein for carbohydrate while holding fat constant,38,42,43 the higher-protein diets led to improvements in weight loss, triglycerides, and HDL-C and increased satiety. In the OmniHeart study, under weight-stable conditions, blood pressure–lowering benefits were observed for a high-protein relative to a high-carbohydrate diet.44 Therefore, the reported effects of the current study should be interpreted as resulting from the combination of macronutrient changes that occur when following lowvs high-carbohydrate diets, not just changes in carbohydrates alone. For example, greater satiety from the higher protein content of the Atkins diet may have contributed to the benefits observed for that group, although satiety was not assessed. The amount of weight loss at 12 months relative to baseline among all groups was modest at 2% to 5%. However, even modest reductions in excess weight have clinically significant effects on risk factors such as triglycerides and blood pressure and, therefore, can have an important public health impact at the population level.4-6,45,46 Greater success with longterm weight loss is likely dependent on a number of factors beyond macronutrient composition, including improved behavioral strategies, longerterm structured guidance, greater emphasis on increasing energy expenditure (ie, regular physical activity), and addressing societal and environmental factors, such as portion sizes of restaurant meals.45,47-49 Strengths of the current study relative to previous trials include a larger sample size, a 12-month duration, lower attrition rates, the contrast of 4 rather than 2 diets differing in carbohydrate content, and the significant differences in macronutrient intake achieved by the diet groups. Although adherence to the 4 sets of dietary guidelines varied within each treatment group and waned over time, especially for the Atkins and Ornish diets, we believe that the adherence levels obtained are a fair representation of studying the diets and variations in macronutrient intake under realistic conditions and, therefore, increase the external validity of the findings. Other strengths include the extensive dietary assessment and the comprehensive health and risk factor data collected. The restriction of our study to premenopausal women allowed us to avoid possible interactions of effects with sex and menopausal status, but because of our focus on this population, generalizations of findings to other populations should be made with caution. This study also has several limitations. Menstrual cycle timing was not taken into consideration for blood sampling for lipid analyses, which likely increased within-person variability and diminished the ability to detect between-group differences. Moreover, weight-loss trajectories for each group had not stabilized at 12 months; the trajectories of weight change between 6 and 12 months suggest that longer follow-up would likely have resulted in progressively diminished group differences. Other limitations included the lack of a valid and comparable assessment of individual adherence to the 4 different diets, the lack of data on whether participants had familiarity using any of the specific study diets prior to enrolling in the trial, and the lack of assessment of satiety. CONCLUSIONS In this study of overweight and obese premenopausal women, those assigned to follow the Atkins diet had more weight loss and more favorable outcomes for metabolic effects at 1 year than women assigned to the Zone, Ornish, or LEARN diets. Concerns about adverse metabolic effects of the Atkins diet were not substantiated within the 12-month study period. It could not be determined whether the benefits were attributable specifically to the low carbohydrate intake vs other aspects of the diet (eg, high protein intake). While questions remain about longterm effects and mechanisms, these findings have important implications for clinical practice and health care policy. Physicians whose patients initiate a low-carbohydrate diet can be reassured that weight loss is likely to be at least as large as for any other dietary pattern and that the lipid effects are unlikely to be of immediate concern. As with any diet, physicians should caution patients that long-term success requires permanent alterations in energy intake and energy expenditure, regardless of macronutrient content.
Author Contributions: Drs Gardner and Balise had full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis. Study concept and design: Gardner, Kraemer, King. Acquisition of data: Gardner. Analysis and interpretation of data: Gardner, Kiazand, Alhassan, Kim, Stafford, Balise, Kraemer, King. Drafting of the manuscript: Gardner, Kiazand, Balise, Kraemer, King. Critical revision of the manuscript for important intellectual content: Gardner, Kiazand, Alhassan, Kim, Stafford, Kraemer, King. Statistical analysis: Gardner, Alhassan, Stafford, Balise, Kraemer. Obtained funding: Gardner, King. Administrative, technical, or material support: Kiazand. Study supervision: Gardner. Financial Disclosures: None reported. Funding/Support: This investigation was supported by National Institutes of Health grant R21AT1098, by a grant from the Community Foundation of Southeastern Michigan, and by Human Health Service grant M01-RR00070, General Clinical Research Centers, National Center for Research Resources, National Institutes of Health. Role of the Sponsor: None of the funding agencies played any role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; or preparation, review, and approval of the manuscript. Acknowledgment: We gratefully acknowledge the work of the study staff who worked with participants in recruitment, intervention, and data collection, including Rise Cherin, MS, RD, Kathryn Newell, MS, Suzanne Olson, MS, Jennifer Morris, PhD, Jane Borchers, MS, RD, Laurie Ausserer, MS, Ellen DiNucci, MA, Kelly Boyington, Jana Stone, Andrea Vaccarella, RD, Noel Segali, RD, and Gretchen George, MS, RD, all of Stanford University, as well as the staff of the Stanford University Hospital General Clinical Research Center. 976 JAMA, March 7, 2007—Vol 297, No. 9 (Reprinted) ©2007 American Medical Association. All rights reserved. Downloaded from www.jama.com at Univ of California -Davis, on March 6, 2007 ONE-YEAR EFFECT OF WEIGHT-LOSS DIETS
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