Vegetarian Nutrition

VN: Types and Diversity of Vegetarian Diets (2009)

Citation:

Martins Y, Pliner P, O'Connor R. Restrained eating among vegetarians: Does a vegetarian eating style mask concerns about weight? Appetite. 1999 Feb; 32 (1): 145-154.

PubMed ID: 9989924
 
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:

The objective of this cross-sectional study was to examine the relationships among dietary style (category of vegetarianism), cognitive eating restraint (conscious control of eating behavior for weight control), and attitudes towards feminism among both women and men.

Inclusion Criteria:

Men or women between the ages of 14 to 45 years.

Exclusion Criteria:

Exclusion criteria are not specified.

Description of Study Protocol:

Recruitment

A convenience sample of participants was recruited using a snowball sampling technique.

Design

Cross-sectional

Statistical Analysis

T-tests were used to compare difference between men and women for eating restraint scores, feminism scores and activity level scores. Multiple regression analyses were used to regress eating style score on (1) eating restraint scores (independent variable); (2) feminism score (moderator variable) and (3) their interaction (eating restraint score X feminism score). All multiple regression analyses were carried out separately for men and women. 

Data Collection Summary:

Timing of Measurements

All measurements occurred at one point in time.

Dependent Variable

Eating style question: One question requiring participants to indicate they “degree of vegetarianism” from one of six categories, ranging from one (non-vegetarian) to six (vegan) (higher scores indicate greater degree of vegetarianism).

Independent Variable

The restraint subscale of the Three Factor Eating Questionnaire (TFEQ): 21 items assessing the conscious control of eating behavior for the purpose of weight control (higher scores indicate greater dietary restraint).

Moderator Variable

Attitudes Toward Feminism Scale (ATFS) (short form): 10 items on a five-point Likert Scale that examine beliefs in traditional sex-role norms and anti-feminine stereotypes (higher scores indicate greater feminism values).

Other Variables

Participants were asked to estimate the total number of hours they spent engaging in physical activity in a typical week. Demographic variables included gender, age and education level.

Description of Actual Data Sample:

N

A total of 227 individuals participated in the study. 

Gender

158 females, 68 males, one not reported.

Age

  • 20.3% were 14 to 19 years
  • 50.7% were 20 to 24 years
  • 12.8% were 25 to 29 years
  • 7.5% were 30 to 34 years
  • 6.2% were 35 years and above
  • 2.6% not reported.

Self-reported vegetarian status

  • Non-vegetarians: 63 females, 42 males
  • Semi-vegetarians: 42 females, seven males
  • Strict vegetarians: 51 females, 19 males.

Ethnicity

Unknown

Location

Not reported; assumed to be Canada.

 

Summary of Results:

Differences between men and women for restraint scores, feminism scores and activity level scores

As indicated in Table 1, compared to females, males had lower restraint scores, less acceptance of feminist values, and engaged in more physical activity on a weekly basis.

Table 1.

Variables Males (n=68)
Means (S.D.)
Females (n=158)
Means (S.D.)
P-value
Eating restraint score 6.04 (5.08) 8.82 (5.92) <0.05
Feminist values 37.69 (8.62) 44.80 (5.38) <0.05
Physical activity
(hours per week)
6.54 (4.32) 4.74 (3.97) <0.05

Table 2 illustrates the multiple regression analyses for men and women.

Table 2.

Models Men (n=68) ALL Women (n=158) Low feminists women
(n=?)
High feminist women (n=?)
Relationship among restraint scores and eating style R2=0.25, P<0.01; β=0.13, P<0.01 not provided R2=0.10, P<0.01; β=0.00, NS R2=0.10, P<0.01; β=0.05, P<0.05
Relationship among feminism and eating style R2=0.25, P<0.01; β=0.05, P<0.05 not provided not provided not provided
Relationship among interaction term (restraint score x feminism) and eating style R2=0.25, P<0.01; β=5.57, NS R2=0.10, P<0.01; β=0.01, P<0.05 not provided not provided

In an additional regression analyses for women, the degree of vegetarianism was regressed on restraint scores, activity level scores, feminism scores, age of participant and all possible interactions; the interaction  between restraint score X feminism approached significance (R2=0.19, P<0.01; β=0.01, P<0.08).

In the regression analyses for both men and women, the models accounting for physical activity variables and related interaction terms were not significant. This indicates the relationship between dietary restraint and degree of vegetarianism did not differ as a function of physical activity.

Author Conclusion:

Findings from this research are based on a non-random sample, which limits generalizability.

As predicted, for males a strong positive relationship was found between dietary restraint and degree of vegetarianism, indicating that as the conscious control of eating for the purpose of weight control increased, so did the degree of vegetarianism. Among women, the relationship between dietary restraint and degree of vegetarianism was moderated by feminism. Dietary restraint and vegetarianism were not related in women with low levels of feminism. However, among women with high feminism, those who were low in restraint have a smaller degree of vegetarianism, whereas those with high restraint exhibited a greater degree of vegetarianism. These data indicate that higher levels of vegetarianism are associated with higher levels of restraint, but only for women who are high in feminism.

The results support the premise that the relationship between dietary restraint and vegetarianism is evident only for those groups whom dieting is socially unacceptable, including women high in feminist and men.

Funding Source:
University/Hospital: University of Toronto at Mississauga, Canada
Reviewer Comments:

The two biggest concerns with this paper is the lack of a representative sample and not accounting for demographic characteristics (socioeconomic status, age, etc.) in all the regression models. While income information was not assessed, level of education achievement was assessed, but not included in the regression models. Socioeconomic status seems to be an important confounding issue related to the proposed research questions. It is not clear why age was not accounted for.

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? 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? No
  1.3. Were the target population and setting specified? No
  2. Was the selection of study subjects/patients free from bias? No
2. Was the selection of study subjects/patients free from bias? No
  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? No
  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? No
  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? No
  2.4. Were the subjects/patients a representative sample of the relevant population? No
  3. Were study groups comparable? No
3. Were study groups comparable? No
  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? ???
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? ???
  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? No
  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? No
  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.) No
  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.) No
  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? 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? 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.) 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? Yes
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? Yes
  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? 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? 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? 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? 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? 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? No
8. Was the statistical analysis appropriate for the study design and type of outcome indicators? No
  8.1. Were statistical analyses adequately described and the results reported appropriately? No
  8.1. Were statistical analyses adequately described and the results reported appropriately? No
  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)? 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? No
  9.2. Are biases and study limitations identified and discussed? No
  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