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Adult Weight Management

VN: Therapeutic Vegetarian Diets and Attrition (2009)

Citation:

Dansinger ML, Gleason JA, Griffith JL, Selker HP, Schaefer EJ. Comparison of the Atkins, Ornish, Weight Watchers, and Zone diets for weight loss and heart disease risk reduction. JAMA 2005; 293: 43-53.

PubMed ID: 15632335
 
Study Design:
Randomized controlled trial
Class:
A - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:

To assess adherence rates and the effectiveness of four popular diets (Atkins, Zone, Weight Watchers and Ornish) for weight loss and cardiac risk factor reduction.

Inclusion Criteria:
  • Overweight or obese adults with BMI 27 to 42
  • Aged 22 to 72 years
  • Known hypertension, dyslipidemia or fasting hyperglycemia
  • Defined as having at least one of the following risk factors:
    • Fasting glucose of at least 110mg per dL
    • Total cholesterol of at least 200mg per dL
    • LDL cholesterol of at least 130mg per dL
    • HDL cholesterol of at least 40mg per dL
    • Triglycerides of at least 150mg per dL
    • Systolic blood pressure of at least 90mmHg
    • Current use of oral medication to treat hypertension, diabetes mellitus or dyslipidemia.
Exclusion Criteria:
  • Unstable chronic illness
  • Insulin therapy
  • Urinary micro-albumin of more than two times normal
  • Serum creatinine of at least 1.4mg per dL
  • Clinically-significant abnormalities of liver or thyroid test results
  • Weight-loss medication
  • Pregnancy.
Description of Study Protocol:
  • Recruitment: Recruited using newspaper advertisements and television publicity
  • Design: Single-center randomized controlled trial. Randomized according to computer-generated Latin square sequence.
  • Blinding used: Study personnel blinded to dietary assignments until after each class roster was finalized. Participants blinded to timing of assessments until two weeks before each visit. Nurses and lab personnel blinded to subject assignment.
  • Intervention: Assignment to Atkins, Zone, Weight Watchers or Ornish diets for one year. Subjects met in small groups with intervention team (a physician and a dietitian) four times during the first two months. In the first meeting, subjects were provided with written materials, and official diet cookbook. Subsequent meetings aimed to maximize adherence by reinforcing positive dietary changes and addressing barriers to adherence.

Statistical Analysis

  • Using T-tests and two-sided type I error of 0.05, 40 participants in each group would be necessary to achieve 80% power to detect a weight change of 2% from baseline or 3% between diets
  • ANOVA used to assess differences in baseline variables and independent T-tests used to compare baseline variables between study participants who discontinued study
  • Absolute changes for each outcome variable at two, six and 12 months were normally distributed for weight loss and cardiac risk variables, but not for dietary variables
  • One-sample T-test for normally-distributed variables and Wilcoxon rank sum test for skewed variables
  • Missing data replaced with baseline data for primary intent-to-treat analysis or excluded for a secondary completers analysis
  • To compare adherence data, Pearson correlation co-efficients were used in a single analysis, pairing the two mean scores for each diet across five time-points
  • Linear regression was used to assess the relationship between changes in weight, dietary adherence variables and cardiac risk factors and to assess the independent effects of potentially confounding variables, including baseline characteristics and changes in exercise and medication use.
Data Collection Summary:

Timing of Measurements

  • Two months of maximal dietary intervention effort
  • Outcome measures assessed at baseline, two, six and 12 months.

Dependent Variables

  • Body weight measured on a single calibrated scale; subjects wearing light clothing and no shoes
  • Waist size as the mean of two readings at umbilicus, using spring-calibrated tape measure
  • Blood pressure measured as mean of one reading in each arm while subject was sitting
  • Cardiac risk factors
  • Fasting blood samples analyzed for total and HDL cholesterol, triglycerides, glucose, insulin, C-reactive protein and creatinine
  • LDL-cholesterol calculated using Friedewald equation
  • Urinalysis of total protein, nitrogen and creatinine levels.

Independent Variables

  • Atkins (under 20g per day carbohydrate restriction, gradual increase to 50g per day), Zone (40% kcal from carbohydrate, 30% from protein, 30% from fat), Weight Watchers (calorie restriction) or Ornish (10% fat, emphasizing vegetarian diets). After two months of maximal effort (RD and MD one-hour group meetings four times during the first two months), subjects chose own level of adherence. Three-day food records completed at baseline, one, two, six and 12 months. Telephoned participants monthly for self-rated adherence level.
  • All groups given standard recommendations for exercise (60 minutes per week), external support and supplements.
Description of Actual Data Sample:
  • Initial N: 1,010 telephone inquiries, 247 screened in person. 160 participants randomly assigned to four groups, 81 were women.
  • Attrition (final N): 93 completers after one year (58% overall completion)
  • Age: Mean, 49±11 years (range 22 to 72 years) 
  • Ethnicity: Not mentioned
  • Anthropometrics: No significant differences between groups at baseline
  • Location: Boston, Massachusetts.
Summary of Results:

Attrition Rate

Even though a large proportion of subjects had discontinued the diets by 12 months, the differences between the diet groups did not reach statistical significance.

  • Atkins: 48%
  • Ornish (vegetarian): 50%
  • Zone: 35%
  • Weight Watchers: 35%.

Outcomes at 12 Months for All Subjects

The different diets showed significant changes from baseline values on many outcome variables, even when the baseline values were carried forward in the case of missing data. There were no statistically significant differences between diets in terms of the outcome variables at one year. HDL changes approached significance (P<0.06).

The results presented below are for all subjects. Baseline values of subjects who dropped out were carried forward. Dansinger and his colleagues also provide outcomes for subjects with no missing values only. As might be expected, when the missing values were dropped, the changes became more pronounced. The more conservative numbers are presented in the table below.


 

Atkins

Zone

Weight
Watchers

Ornish
(Vegetarian)

Between-
Group
Significance

Change in Blood Lipids from Baseline

Total Cholesterol, mg/dL

-4.3 (23)

-10.1 (35)

-8.2 (24)

-10.8 (21)

NS

LDL Cholesterol, mg/dL

-7.1 (24)

-11.8 (34)

-9.3 (27)

-12.6 (19)

NS

HDL Cholesterol, mg/dL

3.4 (7.1)

3.3 (10.3)

3.4 (9.9)

-0.5 (6.5)

NS (0.06)

Total-to-HDL Ratio -0.39 (0.69) -0.52 (1.04) -0.7 (1.67) -0.3 (0.96) NS
LDL-to-HDL Ratio -0.39 (0.81)  -0.4 (0.81) -0.55 (1.39)  -0.31 (0.68) NS

Triglycerides, mg/dL

-1.2 (84)

2.5 (147)

-12.7 (61)

5.6 (36)

NS

Body Composition

Weight, kg

-2.1 (4.8)

-3.2 (6.0)

-3.0 (4.9)

-3.3 (7.3)

NS

BMI

-0.7 (1.6)

-1.1 (2.0)

-1.1 (1.7)

-1.4 (2.5)

NS

Waist Circumference, cm

-2.5 (4.5)

-2.9 (5.3)

-3.3 (5.4)

-2.2 (5.5)

NS

Blood Pressure

Systolic BP, mmHg

0.2 (12)

1.4 (15)

-2.7 (13)

0.5 (7.7)

NS

Diastolic BP, mmHg

-1.4 (7.5)

-1.2 (9.5)

-1.7 (6.4)

0.2 (4.6)

NS

Other Outcomes

Glucose, mg/dL

1.4 (30)

-4.2 (18)

-4.7 (19)

-4.1 (30)

NS

Insulin, μIU/ml

-1.2 (6.7)

-5.4 (14)†

-2.6 (6.1)

-3.0 (6.3)

NS

C-reactive Protein, mg/L

-0.70 (2.1)

-0.58 (2.1)

-0.58 (1.3)

-0.88 (2.4)

NS

 indicates a statistically-significant decrease from baseline
 indicates a statistically-significant increase from baseline.

Other Findings

  • At one year, the mean caloric reductions from baseline were 138 for Atkins, 251 for Zone, 244 for Weight Watchers and 192 for Ornish (all P<0.05, P=0.70 between diets)
  • Assuming no change from baseline for participants who discontinued the study, mean weight loss at one year was 2.1±4.8kg for Atkins [21 of 40 (53%) participants completed, P=0.009]. 3.2±6.0kg for Zone [26 of 40 (65%) participants completed, P=0.002], 3.0±4.9kg for Weight Watchers [26 of 40 (65%) participants completed, P<0.001] and 3.3±7.3kg for Ornish [20 of 40 (50%) participants completed, P=0.007]. There were no statistically significant differences between diets.
  • Greater effects were observed in study completers
  • Each diet significantly reduced the LDL-to-HDL-cholesterol ratio by approximately 10% (all P<0.05), with no significant effects on blood pressure or glucose at one year
  • Amount of weight loss was associated with self-reported dietary adherence level (R=0.60, P<0.001), but not with diet type (R=0.07, P=0.40)
  • For each diet, decreasing levels of total and HDL cholesterol, C-reactive protein and insulin were significantly associated with weight loss (mean R=0.36, 0.37 and 0.39, respectively), with no significant difference between diets (P=0.48, P=0.57, P=0.31, respectively).
Author Conclusion:
  • In conclusion, poor sustainability and adherence rates resulted in modest weight loss and cardiac risk factor reduction for each diet group as a whole
  • Cardiac risk factor reductions were associated with weight loss, regardless of diet type, underscoring the concept that adherence level, rather than diet type, was the key determinant of clinical benefit
  • Cardiovascular outcomes studies would be appropriate to further investigate the potential health effects of these diets
  • More research is also needed to identify practical techniques to increase dietary adherence, including techniques to match individuals with the diets best suited to their food preferences, lifestyle and medical conditions.
Funding Source:
Government: NIH
Reviewer Comments:

High overall drop-out rate, but that was one of the study purposes.

Quality Criteria Checklist: Primary Research
Relevance Questions
  1. Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies) Yes
  1. Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies) Yes
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? Yes
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? Yes
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice? Yes
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice? Yes
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) Yes
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) Yes
 
Validity Questions
  1. Was the research question clearly stated? Yes
1. Was the research question clearly stated? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? Yes
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? Yes
  1.3. Were the target population and setting specified? Yes
  2. Was the selection of study subjects/patients free from bias? Yes
2. Was the selection of study subjects/patients free from bias? Yes
  2.1. Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study? Yes
  2.1. Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study? Yes
  2.2. Were criteria applied equally to all study groups? Yes
  2.2. Were criteria applied equally to all study groups? Yes
  2.3. Were health, demographics, and other characteristics of subjects described? Yes
  2.3. Were health, demographics, and other characteristics of subjects described? Yes
  2.4. Were the subjects/patients a representative sample of the relevant population? Yes
  2.4. Were the subjects/patients a representative sample of the relevant population? Yes
  3. Were study groups comparable? Yes
3. Were study groups comparable? Yes
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) Yes
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) Yes
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? Yes
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? Yes
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) Yes
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) Yes
  3.4. If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis? N/A
  3.4. If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis? N/A
  3.5. If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.) N/A
  3.5. If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.) N/A
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? N/A
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? N/A
  4. Was method of handling withdrawals described? Yes
4. Was method of handling withdrawals described? Yes
  4.1. Were follow-up methods described and the same for all groups? N/A
  4.1. Were follow-up methods described and the same for all groups? N/A
  4.2. Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.) Yes
  4.2. Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.) Yes
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? Yes
  4.4. Were reasons for withdrawals similar across groups? Yes
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? N/A
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? N/A
  5. Was blinding used to prevent introduction of bias? Yes
5. Was blinding used to prevent introduction of bias? Yes
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? Yes
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? Yes
  5.2. Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.) Yes
  5.2. Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.) Yes
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? N/A
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? N/A
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? N/A
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? N/A
  5.5. In diagnostic study, were test results blinded to patient history and other test results? N/A
  5.5. In diagnostic study, were test results blinded to patient history and other test results? N/A
  6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? Yes
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? Yes
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? Yes
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? Yes
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? N/A
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? N/A
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? Yes
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? Yes
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? Yes
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? Yes
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? Yes
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? Yes
  6.6. Were extra or unplanned treatments described? Yes
  6.6. Were extra or unplanned treatments described? Yes
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? Yes
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? Yes
  6.8. In diagnostic study, were details of test administration and replication sufficient? N/A
  6.8. In diagnostic study, were details of test administration and replication sufficient? N/A
  7. Were outcomes clearly defined and the measurements valid and reliable? Yes
7. Were outcomes clearly defined and the measurements valid and reliable? Yes
  7.1. Were primary and secondary endpoints described and relevant to the question? Yes
  7.1. Were primary and secondary endpoints described and relevant to the question? Yes
  7.2. Were nutrition measures appropriate to question and outcomes of concern? Yes
  7.2. Were nutrition measures appropriate to question and outcomes of concern? Yes
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? Yes
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? Yes
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? Yes
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? Yes
  7.5. Was the measurement of effect at an appropriate level of precision? Yes
  7.5. Was the measurement of effect at an appropriate level of precision? Yes
  7.6. Were other factors accounted for (measured) that could affect outcomes? Yes
  7.6. Were other factors accounted for (measured) that could affect outcomes? Yes
  7.7. Were the measurements conducted consistently across groups? Yes
  7.7. Were the measurements conducted consistently across groups? Yes
  8. Was the statistical analysis appropriate for the study design and type of outcome indicators? Yes
8. Was the statistical analysis appropriate for the study design and type of outcome indicators? Yes
  8.1. Were statistical analyses adequately described and the results reported appropriately? Yes
  8.1. Were statistical analyses adequately described and the results reported appropriately? Yes
  8.2. Were correct statistical tests used and assumptions of test not violated? Yes
  8.2. Were correct statistical tests used and assumptions of test not violated? Yes
  8.3. Were statistics reported with levels of significance and/or confidence intervals? Yes
  8.3. Were statistics reported with levels of significance and/or confidence intervals? Yes
  8.4. Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)? Yes
  8.4. Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)? Yes
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? Yes
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? Yes
  8.6. Was clinical significance as well as statistical significance reported? Yes
  8.6. Was clinical significance as well as statistical significance reported? Yes
  8.7. If negative findings, was a power calculation reported to address type 2 error? Yes
  8.7. If negative findings, was a power calculation reported to address type 2 error? Yes
  9. Are conclusions supported by results with biases and limitations taken into consideration? Yes
9. Are conclusions supported by results with biases and limitations taken into consideration? Yes
  9.1. Is there a discussion of findings? Yes
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? Yes
  9.2. Are biases and study limitations identified and discussed? Yes
  10. Is bias due to study's funding or sponsorship unlikely? Yes
10. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? Yes
  10.2. Was the study free from apparent conflict of interest? Yes