Vegetarian Nutrition

VN: Types and Diversity of Vegetarian Diets (2009)

Citation:

Greene-Finestone LS, Campbell MK, Gutmanis IA, Evers SE. Dietary intake among young adolescents in Ontario: associations with vegetarian status and attitude toward health. Prev Med. 2005 Jan; 40 (1): 105-111.

PubMed ID: 15530587
 
Study Design:
Cross-Sectional Study
Class:
D - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:

To describe the dietary intakes of vegetarian and omnivore teens and determine if and how their attitude toward personal health is related to their food consumption.

Inclusion Criteria:
  • Ninth grade high school students
  • Parental consent.
Exclusion Criteria:

None noted.

Description of Study Protocol:
  • Recruitment: Ninth grade students in high schools in regions of Ontario, Canada
  • Design: Non-experimental descriptive or exploratory survey.

Intervention

Questionnaire used to survey subjects on the following:

  • Food consumption: Used brief 19-item food frequency questionnaire (FFQ)
  • Vegetarian status: Assessed via reported consumption or exclusion of red meats, poultry, fish, eggs and milk products. Vegetarians (VEG) included subjects identified as vegan, ovo-lacto and semivegetarian. 
  • Terms defined
    • Omnivores consume red meat at least monthly
    • Vegans exclude all foods of animal origin
    • Ovo-lacto include eggs and dairy; avoid red meat, poultry and fish                            
    • Semiveg include eggs, dairy, fish and poultry, but avoid red meat.
  • Sociodemographic and personal variables: Sex, age, attitude toward personal health (i.e., very important, somewhat important, not important)
  • Dietary diversity score (DDS): Assessed participants' success in consuming foods from a variety of food groups.

Statistical Analysis

  • Frequency analyses used to report vegetarian (VEG) and omnivore (OMN) prevalence
  • Chi-square analyses, Fisher's Exact tests, and T-tests used to compare vegetarian status with frequency of consumption variables
  • Statistical analysis of females only performed to eliminate possible effect modification of sex (due to VEG group predominantly comprised of females)
  • Using the Mantel-Haenszel Method and Breslow-Day test for homogeneity of odds ratios, the value of the health consciousness variable was explored as a possible effect modifier of the relationship between frequency of food group consumption and vegetarian status
  • Statistical significance set at P<0.05.
Data Collection Summary:

Timing of Measurements

1999.

Factors Examined

  • Diet group: Membership in diet group was identified by the researchers based on food intake, not on self-report
  • Food frequency: Measured using a 19-question food frequency questionnaire
  • Dietary diversity
  • Health attitudes: Student self-report questionnaire.
Description of Actual Data Sample:
  • Initial N: 680 (gender breakdown not provided)
  • Attrition (final N): 630 (286 males, 337 females) (Note: Total N is greater than the sum for males and females as some respondents did not indicate their sex)
  • Age: 13 to 15 years
  • Location: Hamilton-Wentworth and Niagara regions of Ontario, Canada.

 

 

 

Summary of Results:
  • Prevalence of vegetarianism: Females, 6.5% (CI=4.6% to 8.4%); males, 1.0% (CI=0.2% to 1.8%)
  • VEG group consisted of 25 adolescents (4.0%, CI=2.5% to 5.5%), of whom 16 (2.5%, CI=1.3% to 3.7%) were ovo-lacto vegetarian, nine (1.4%, CI=0.5% to 2.3%) were semivegetarian and zero were vegan
  • There were 605 OMN in study.

Comparisons Among Diet Groups

While there were significant food intake differences between omnivores and vegetarians, there were also significant differences between health conscious and non-heath conscious members of each group. Tables 1 and 2 present the differences within each diet group.

Table One: Differences in Food Intake Among Vegetarians
Health-conscious vs non-health-conscious

Percentage Eating at Least Two Servings Per Day of the Following Food Groups

Health Conscious Vegetarians
N=12

Non-Health Conscious Vegetarians
N=11

Significance

Grain Products

58.3%

10%

P<0.05

Vegetables and Fruit

91.7%

45.5%

P<0.05

Milk Products

30%

50%

NS

Meat and Alternatives

63.6%

0%

P<0.05

Diet Diversity Score

3.2±0.97

2.6±1.06

NS

On a Diet

25%

63.6%

 

Table Two: Differences in Food Intake Among Omnivores
Health-conscious vs. non-health-conscious

Percentage Eating at Least Two Servings Per Day of the Following Food Groups

Health Conscious Omnivores
N=433

Non-Health Conscious Omnivores
N=136

Significance

Grain Products

48.8%

37.3%

P<0.05

Vegetables and Fruit

74.4%

60.3%

P<0.05

Milk Products

68.6%

57.1%

P<0.05

Meat and Alternatives

68%

60.5%

 

Diet Diversity Score

3.6±0.66

3.4±0.89

P<0.05

On a Diet

10.1%

7.4%

 

How Do Omnivores and Vegetarians Compare?

  • The only significant (P=0.015) difference between health conscious members of both groups was milk group consumption, with the vegetarians consuming less
  • Among non-health conscious individuals, vegetarians were significantly (P<0.001) less likely to eat meat and alternatives, had a lower diet diversity score (P=0.022), and were more likely to be on a diet (P<0.001)
  • Consumption of a variety of sources of fiber was highest among health-conscious VEG and lowest among non-health conscious VEG.
Other Findings
  • Response rate of schools ranged from 19% to 86%; data from three lowest response schools did not differ significantly on nutrition and health-related issues compared to other schools
  • Intraclass correlations (0.0004 to 0.0037) suggest negligible clustering effect within schools for vegetarian status, self-reported health and dieting in past year
  • 4% (27 of 680) of surveys excluded due to unreliable responses
  • Food frequency questionnaires of 10 subjects (1.5%) were excluded due to poor completion (more than 50% blank responses)
  • Complete data available to categorize vegetarian status of 630 respondents
  • No sex, health, diet or social adjustment differences between those with and without complete flesh food consumption data, except alcohol use was higher among those without complete flesh food consumption (P<0.02).
Author Conclusion:

Large proportions of both vegetarian and omnivore adolescents consumed suboptimal diets. Health consciousness had value as an indicator of dietary adequacy and may be useful as a rudimentary screen for problematic dietary consumption patterns.

Funding Source:
University/Hospital: University of Western Ontario, Southwestern Region Health Information Partnership, University of Guelph (all Canada)
Reviewer Comments:
  • Discrepancy noted regarding initial N and final N. Excluded surveys not all accounted for. 
  • Discrepancy noted regarding definition of term, semivegetarian:
    • Method section defined semivegetarians as "those who include eggs, dairy, fish and/or poultry, but avoid red meat" 
    • However, authors give a slightly different definition in the Discussion section: "Only those reporting red meat consumption as rarely or never were classified as semivegetarians" 
    • To further complicate matters, omnivore was defined as "those consuming red meat at least monthly" 
    • Given these definitions, it seems the terms rarely and never should not have been grouped together on the survey because for some taking the survey, rarely might have been interpreted as "once per month." 
  • This may be why there were so many OMN (605), and so few semivegetarians (nine), identified in this study. 

Limitations

  • Sample of vegetarians was limited and further reduced by stratification based on health-consciousness
  • Due to limited sample of VEGs, representativeness of the groups is uncertain and caution should be exercised in interpreting results
  • Small size of VEG sample did not allow for study of sex as an interaction with frequency of food group consumption
  • Study results should be confirmed using larger sample size
  • Uneven response rate within schools, which could affect survey's external generalizability 
  • Impact of nonresponse bias is unknown because characteristics of the respondents and nonrespondents could not be compared
  • Food frequency questionnaire is not comprehensive, leading to assumptions around portion sizes, and does not account for the consumption of all foods. Results would need to be confirmed using multiple 24-hour recalls or a food frequency questionnaire that has been validated with adolescents against actual intakes as determined by other methods or repeat measures.

In this study, "vegetarian" (VEG) was defined as and included subjects identified as vegan, ovolactovegetarian and semivegetarian.

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) N/A
  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) N/A
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? ???
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? ???
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice? No
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice? No
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) N/A
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) N/A
 
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? N/A
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? N/A
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? N/A
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? N/A
  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? No
  2.3. Were health, demographics, and other characteristics of subjects described? No
  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) N/A
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) N/A
  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.) N/A
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) 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? 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? Yes
  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.) Yes
  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.) Yes
  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? No
4. Was method of handling withdrawals described? No
  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%.) 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%.) N/A
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? No
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? No
  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? 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? N/A
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? N/A
  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.) 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.) No
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? No
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? No
  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? N/A
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? N/A
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? Yes
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? Yes
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? N/A
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? N/A
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? N/A
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? N/A
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? N/A
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? N/A
  6.6. Were extra or unplanned treatments described? N/A
  6.6. Were extra or unplanned treatments described? N/A
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? N/A
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? N/A
  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? No
  7.2. Were nutrition measures appropriate to question and outcomes of concern? No
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? N/A
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? N/A
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? ???
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? ???
  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)? N/A
  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)? N/A
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? N/A
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? N/A
  8.6. Was clinical significance as well as statistical significance reported? N/A
  8.6. Was clinical significance as well as statistical significance reported? N/A
  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? No
  10.1. Were sources of funding and investigators' affiliations described? No
  10.2. Was the study free from apparent conflict of interest? Yes
  10.2. Was the study free from apparent conflict of interest? Yes