This Academy member benefit temporarily has been made public to allow all practitioners access to content that may assist in patient care during the national pandemic response. Click here for information on joining the Academy. 

Vegetarian Nutrition

VN: Therapeutic Vegetarian Diets and Attrition (2009)

Citation:

Barnard, ND, Scialli, AR et al. Effectiveness of a low-fat vegetarian diet in altering serum lipids in healthy premenopausal women. Am J of Cardiology. 2000 (Apr); 85: 969-972.

 

PubMed ID: 10760336
 
Study Design:
Randomized Crossover Trial
Class:
A - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:

To investigate whether following a low-fat vegetarian diet would lower total and LDL cholesterol concentrations in healthy pre-menopausal women.

Inclusion Criteria:
  • Pre-menopausal females
  • At least 18 years old
  • Exhibiting moderate to severe pain accompanying menstrual periods
  • Already participating in a study examining the effect of a low-fat vegetarian diet on serum sex-hormone-binding globulin concentration and dysmenorrhea.
Exclusion Criteria:
  • Irregular menstrual cycles
  • Menstrual cycles of either less than 25 days or more than 35 days
  • Physical illness affecting eating behavior or causing pain
  • History of hormone-related illness, e.g., diabetes or thyroid disease
  • History of mental illness
  • Alcohol or drug abuse
  • Use of oral contraceptives in previous six months
  • Use of drugs known to affect hormonal function in previous six months
  • Structural abnormality that could account for abdominal pain.
Description of Study Protocol:

Recruitment

  • Newspaper advertisements
  • Notices mailed to gynecologists
  • Washington, DC area
  • No monetary compensation provided.

Design RCT Crossover Design

  • Randomization done by computer-generated random number list
  • Two groups (N=24, N=27)
  • Received the same treatments, but in opposite order
    • Initial baseline period lasting one full menstrual cycle; no dietary changes
    • Two successive replications, each lasting two full menstrual cycles
      • Diet intervention phase using a low-fat vegetarian diet
      • Placebo "supplement" phase.

Special Diet Prescriptions or Modifications

Nutrients Intervention (Vegetarian or Vegan) Usual Diet with Placebo Supplement
Energy None None
Protein None None
Carbohydrates None None
Fat/fatty acids Approximately 10% None
Other

Grains, vegetables, legumes and fruits.

Avoid
Animal products, added oils, fried foods, avocados, olives, nuts, nut butters and seeds

None
Supplements B12 (2 micrograms) None

Length of Treatment

Two menstrual cycles (approximately eight weeks).

Follow-Up

None reported.

Behavioral Interventions

Weekly one-hour nutrition training and support meetings throughout study duration

  • Cooking demonstrations
  • Lectures
  • Grocery samples of vegetarian foods occasionally provided during diet intervention phase
  • Spouses or partners of subjects were invited.

Blinding Used

Subjects blinded to the nature of the supplement (B12 or placebo).

Intervention

  • Dietary intervention consisting of a low-fat (under 10% calories from fat) vegetarian diet
    • Foods allowed:
      • Grains
      • Vegetables
      • Legumes
      • Fruits.
    • Foods not allowed:
      • Animal products
      • Added oils
      • Fried foods
      • Avocados
      • Olives
      • Nuts
      • Nut butters
      • Seeds.

Statistical Analysis

  • Within-subjects analyses of variance to assess effect of the intervention diet
  • For each variable, analyses were conducted on the change scores obtained from:
    • Difference between baseline and intervention diet phase
    • Difference between baseline and supplement phase.
  • Significant difference indicated that change from baseline to intervention was different from change from baseline to supplement
  • Results reported as means±SD
  • Significance: P<0.05
  • Order effects of interventions tested also; method not described.
Data Collection Summary:

Timing of Measurements

  • Interventions
    • Initial baseline period with no dietary changes, lasting one full menstrual cycle
    • Two intervention phases, each lasting two full menstrual cycles.
  • Three-day dietary record
    • Two weekdays and one weekend day
    • Recorded by subject between Days Six and 14 of menstrual cycle.
  • Body weight measured
    • Measured on a single occasion
    • Between Days 14 and 21 of menstrual cycle
    • In street clothes
    • Measured to nearest 0.2kg
    • Same scale used during each study phase. 
  • Blood sample collection
    • On Day Six of each participant's menstrual cycle
    • Serum separated and frozen
    • Laboratory determinations for all participants during each replication were run in the same batch at the end of the study.

Dependent Variables

  • Serum lipids (total cholesterol, LDL, HDL), measured in mg per dL, were the primary dependent variables
  • The researchers also measured changes in body weight and BMI.

Independent Variables

Low-fat vegetarian diet with approximately 10% of calories derived from fat.

Description of Actual Data Sample:
  • Initial N: 51 pre-menopausal females
  • Attrition (final N): 31.

Reasons for Non-Completion

  • Onset of menopause: One
  • Pregnancy: One
  • Repeatedly missing meetings: Two
  • Non-compliance with intervention diet: Two
  • Extended travel or scheduling difficulties: Two
  • Death in the family: One
  • Major financial problems: One
  • Spouse objections to diet: One
  • Unknown reason: One
  • Exclusion from data analysis for not returning all data forms: Four.

Age

22 to 48 years old (mean, 36.1).

Ethnicity 

  • White, non-Hispanic: 21
  • Black, non-Hispanic: Nine
  • White, Hispanic: Four
  • Black, Hispanic: Zero
  • Asian: One.

Other Relevant Demographics

  • Single: 24
  • Married: Eight
  • Separated, divorced, widowed: Three
  • Mean age of menarche: 12.3 years
  • Pregnancies (median, range): Zero, zero to 13
  • Live births (median, range): Zero, zero to two
  • Living children (median, range): Zero, zero to two.

Anthropometrics

No significant differences on important measures.

Location

Washington, DC area.

Summary of Results:

 Summary

  • Total and LDL cholesterol decreased by 13.2% and 16.9%, respectively, from baseline to intervention (P<0.001)
  • Changes in cholesterol were not associated with baseline BMI or change in BMI
  • HDL decreased 16.5%
  • LDL-to-HDL ratio remained unchanged
    • Mean serum triacylglycerol concentration increased 18.7% (P<0.001) from baseline to intervention, but remained under one
    • One mmol per L throughout the study.
  • Intake of other nutrients during intervention diet phase:
    • Calcium intake decreased (P<0.001)
    • Sodium intake decreased (NS)
    • Protein intake decreased (P<0.01)
    • Due to decreased sodium and protein intake, renal losses were reduced, favoring improved calcium balance.

Intake Results

Nutrient

Baseline or Prescribed

Usual Diet with Placebo (Actual Intake)

Vegan/Vegetarian (Actual Intake)

Nutrients

Energy (mJ or kcal)

7.9 (1.8)

7.3 (2.0)

6.4 (1.6)*

Protein (g)

67 (20)

60 (17)

43 (11)+

Carbohydrates (g)

295 (76)

283 (91)

311 (89)

Total Sugar (g)

110 (42)

101 (45)

109 (38)+

Total Fiber (g)

26 (9)

23 (11)

31 (9)

Fat (g)

52 (24)

43 (23)

17 (10)+

Saturated Fat (g)

15(12)

12 (10)

3 (3)+

Polyunsaturated Fat (g)

9 (6)

9 (5)

4 (3)+

Cholesterol (mg)

132 (137)

132 (91)

6 (8)+

Micronutrients

Sodium (mg)

2,640 (880)

2,400 (790)

2,170 (770)

Calcium (mg)

750 (331)

658 (283)

466 (199)

Pyridoxine (mg)

2.5 (3.1)

2.5 (2.5)

4.9 (16.9)+

Foods

Caffeine

97 (107)

82 (104)

57 (70)

Outcomes

Variables

Baseline

Usual Diet with Placebo Supplement

Low-Fat Vegetarian Diet with B12 Supplement

Statistical Significance of Difference Between Baseline and Vegetarian Diet

Total Cholesterol (mg/dL)

163±30

162±36

141±36

P<0.001

HDL (mg/dL) 

49±11

52±15

41±13

P<0.001

LDL (mg/dL)

97±24

94±29

80±26

P<0.001

VLDL (mg/dL)

16±7.3

16±7.5

19±10.4

P<0.001

Triacylglycerol (mg/dL)

81±36

81±38

97±52

P<0.01

LDL/HDL

2.0±0.7

1.9±0.8

2.0±0.7

NS

Weight (kg)

69.4±12.9

68.5±13.0

66.9±12.5

P<0.001

BMI (kg/m2)

25.5 ± 5.2

25.2±5.2

24.6±4.9

P<0.001

Other Findings

  • Order of diet presentation influenced results: Weight lost during low-fat vegetarian diet phase not fully regained during subsequent usual diet plus placebo phase
  • Weight change during diet phase was associated with changes in energy intake
  • Significant correlation between initial BMI and subsequent weight loss during the diet intervention.

Initial BMI (kg/m2)

Weight Loss (kg)

Less than 22.0 1.4
22.0 to 26.5 3.3
More than 26.5 2.9

Author Conclusion:

Following a low-fat vegetarian diet results in significant reductions in serum total and LDL concentrations and significant weight-loss in the short term (within six months) in healthy, free-living pre-menopausal women.

Funding Source:
Government: NIDDK
Reviewer Comments:
  • This is a study within a larger study investigating the effect of a low-fat vegetarian diet on serum sex-hormone-binding globulin concentration and dysmenorrhea
  • The investigators reported limitations:
    • Study did not address long-term clinical effects of diet
    • Diet may not be sustainable long-term
    • Food consumption may have been under-reported
    • Participants' symptomatology may have increased their motivation
    • Participants may have been knowledgeable about nutrition.
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")? Yes
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? Yes
  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%.) No
  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%.) No
  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? 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? 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? Yes
  5.5. In diagnostic study, were test results blinded to patient history and other test results? Yes
  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? Yes
  6.8. In diagnostic study, were details of test administration and replication sufficient? Yes
  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? ???
  8.2. Were correct statistical tests used and assumptions of test not violated? ???
  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)? No
  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)? No
  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? 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? ???
  10.2. Was the study free from apparent conflict of interest? ???