Vegetarian Nutrition

VN: Therapeutic Vegetarian Diets and Attrition (2009)

Citation:

Turner-McGrievy GM, Barnard ND, Scialli AR. A two-year randomized weight loss trial comparing a vegan diet to a more moderate low-fat diet. Obesity (Silver Spring). 2007 Sep; 15 (9): 2,276-2,281.

PubMed ID: 17890496
 
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 the effect of a low-fat, vegan diet compared with the National Cholesterol Education Program (NCEP) diet on weight-loss maintenance over one- and two-year periods.

Inclusion Criteria:
  • Female
  • Overweight or obese (BMI 26kg to 44 kg/m2)
  • Post-menopausal.

 

Exclusion Criteria:
  • Pre-menopausal
  • Unstable medical status
  • History of eating disorder
  • History of substance abuse
  • Severe mental illness
  • Previously diagnosed diabetes
  • Physical conditions affecting body weight (e.g., Cushing's disease)
  • Recent use of estrogens
  • Intake of medications affecting appetite
  • Intake of medications affecting body weight
  • Tobacco use
  • Already following a vegan diet.
Description of Study Protocol:

Recruitment

Newspaper advertisements in the Washington, DC area.

Design

RCT; Random number table used to assign participants to either vegan or NCEP diet.

Two replications

  • Replication number one (unsupported):
    • N=28
    • Initial 14-week dietary intervention
    • No support group meetings after the initial intervention.
  • Replication number two (supported):
    • N=34
    • Initial 14-week dietary intervention
    • Support group meetings for one hour every two weeks for one year after the initial intervention.

Blinding Used

NA.

Intervention

  • 14-week dietary intervention
  • No restriction on energy intake
  • Participants encouraged to eat to satiety
  • No meals were provided
  • Participants encouraged to maintain usual physical activity levels during 14-week intervention
  • Weekly group meeting of all participants with the physician and registered dietitian
    • Instruction in nutrition and meal preparation
    • Participants provided with:
      • Diet sheets listing allowed and disallowed foods
      • Recipes
      • Tips for following assigned diets at home, work, at restaurants and while traveling.
  • Two diet groups in each replication
    • Vegan
      • Low-fat
      • Fruits
      • Vegetables
      • Legumes
      • Grains
      • No animal products
      • Use of unrefined foods encouraged
      • Limited high-fat plant foods; e.g., avocados, nuts and seeds.
    • NCEP: Guidelines of the former NCEP Step II [similar to current Therapeutic Lifestyle Changes (TLC) diet]. 

Statistical Analysis

  • Analyses were done on an intention-to-treat basis by bringing the last value forward. Included all participants with baseline data:
    • 31 vegan (17 supported and 14 unsupported)
    • 31 NCEP (17 supported and 14 unsupported).
  • Change scores were calculated between baseline and one-year weights and baseline and two-year weights
  • Weight loss reported as median (interquartile range). Weight loss is the difference between weight at baseline and at one and two years.
  • Non-parametric statistical tests (α set at 0.05) were used because of skewed distributions for some data. Statistical tests:
    • Student T-test used for age
    • Χ2 used for other demographic data
    • Wilcoxon test used for weight and weight change
    • Weight changes were calculated within and between:
      • Vegan and NCEP diet groups
      • Supported and unsupported participants
      • Meeting attendees and non-attendees
      • Diet adherers and non-adherers.
  • Statistical significance: P<0.05.
Data Collection Summary:

Timing of Measurements

Baseline and at 14 weeks:

  • Body weight (light clothing, no shoes)
  • Dietary intake for two weekdays and one weekend day.

At one and two years:

  • Body weight (light clothing, no shoes)
  • Food Frequency Questionnaire (FFQ) was completed to measure diet adherence
    • Four food group categories were assessed for each diet
      • Vegan adherence criteria
        • Up to one dairy serving per week
        • Up to three ounces meat, fish, poultry per week
        • Up to one egg per week
        • Up to two servings of a high-fat item (e.g., mayonnaise, margarine, lard, oil, salad dressings, avocados, olives, nuts, high-fat pastry) per day.
      • NCEP adherence criteria
        • At least five servings of grains per day (one serving plus one slice bread or half-cup cooked grain)
        • At least five servings of fruits and vegetables per day
        • Up to six ounces of lean meat per day
        • Up to two servings of high-fat items (e.g., mayonnaise, margarine, lard, oil, salad dressings, avocados, olives, nuts, high-fat pastry) per day.
    • Participants were scored on the basis of food groups consumed or not consumed
      • Scale of zero to four
      • Four equals highest compliance
      • Scoring at least a three was considered compliant.

Participant attendance was recorded at all meetings.

Follow-up data

  • One-year follow-up data were available for:
    • 26 vegan (17 supported and nine unsupported) participants
    • 27 NCEP (14 supported and 13 unsupported) participants.
  • Two-year follow-up data were available for:
    • 23 vegan (15 supported and 8 unsupported) participants
    • 25 NCEP (17 supported and 11 unsupported) participants.

Dependent Variable

Weight loss (measured in kg).

Independent Variables

  • Two low-fat diets: Vegan and NCEP
  • Social support (group meetings)
  • Diet adherence
  • Meeting attendance.

Control Variables

Group nutrition education sessions during 14-week dietary intervention period.

Description of Actual Data Sample:
  • Initial N
    • 64 females recruited
    • 62 females began the study (N=31 in vegan group; N=31 in NCEP group).
  • Attrition (final N): 59 females completed the study
  • Age
    • Vegan group: 57.4±4.7 years (47 to 71 years)
    • NCEP group: 55.7±6.4 years (44 to 73 years).

Ethnicity

  Vegan Group   NCEP Group  
N Percentage N Percentage
White, Non-Hispanic
20
65
18
58
Black, Non-Hispanic
9
29
12
39
White, Hispanic
0
0
1
3
Other
2
6
0
0

Other Relevant Demographics

  • No significant differences between the diet intervention groups
  • 78% of vegan group and 64% of NCEP group had college or advanced degrees.

Anthropometrics

  • Information on weight was the only anthropometric measure provided
  • Median weight for supported group was higher than for the unsupported group (93.3 vs. 79.5 kg).

Location

Washington, DC area.

Summary of Results:

 Major findings

  • Participants in the vegan group lost more weight than those in the NCEP group at one year (-4.9 kg vs. -1.8 kg; P=0.021) and two years (-3.1 kg vs. -0.8 kg; P=0.022)
  • Vegan group had significant weight loss at both one and two years
  • Supported groups lost more weight than unsupported at one year (-5.5 kg vs. -1.4 kg; P=0.0001) and two years (-3.9 kg vs. -0.4 kg; P=0.016).

Other Findings

  • NCEP group had significant weight loss at one year but not at two years
  • Supported vegans lost more weight than unsupported vegans at both one year and two years
  • Supported NCEP participants lost significantly more weight than unsupported NCEP at one year but not at two years
  • Meeting attendees (attending more than one half of meetings) lost more weight than non-attendees at one year (-6.7 kg vs. -3.3 kg; P=0.001) and two years (-5.8 kg vs. -3.1 kg; P=0.011)
  • No significant difference in weight loss between vegan attendees and non-attendees at either one year or two years
  • No significant difference in weight loss between diet adherers and non-adherers at either one year or two years for both groups combined
  • Within the vegan group there was no significant difference in weight loss between diet adherers and non-adherers at one year but there was a difference at two years (P<0.05).
Author Conclusion:

A low-fat vegan diet is associated with significantly greater weight loss compared with the NCEP diet at both one and two years of follow-up. Group support via meeting attendance assists in sustained weight loss.

Funding Source:
Other: No outside funding or support
Reviewer Comments:
  • Use of a three-day diet record versus FFQ may not provide accurate assessment of dietary intake
  • Body weight, rather than BMI or body composition, was measured.
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? No
  2.4. Were the subjects/patients a representative sample of the relevant population? No
  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? Yes
  4.1. Were follow-up methods described and the same for all groups? 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
  4.2. 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? ???
  4.4. Were reasons for withdrawals similar across groups? ???
  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? No
5. Was blinding used to prevent introduction of bias? No
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? No
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? No
  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? No
  7.6. Were other factors accounted for (measured) that could affect outcomes? No
  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)? No
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? No
  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? N/A
  8.7. If negative findings, was a power calculation reported to address type 2 error? N/A
  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