EAL

VN: Types and Diversity of Vegetarian Diets (2009)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

The objective of this cross-sectional study was to compare vegetarian and non-vegetarian adolescent schoolchildren in Minnesota regarding food intake patterns, disordered eating and other health-compromising and health-promoting behaviors.

Inclusion Criteria:

Adolescent children attending grades seven through 12 in a Minnesota public school. Only participants residing in non-urban areas were included in the analyses.

Exclusion Criteria:

Students residing in urban areas.

Description of Study Protocol:

Recruitment

The study population for the present study was drawn from a larger population who had completed the Minnesota Adolescent Health Survey (MAHS) in 1986 to 1987. The MAHS included 17,544 adolescents age 12 years to 20 years in grades seven through 12 within public schools across Minnesota. The MAHS sampling design was stratified based on student enrollment numbers in all public school districts, then schools were selected at random within each stratum and for each grade.

Design

Cross-sectional.

Statistical Analysis

For all analyses, chi-square tests were used to compare vegetarians with non-vegetarians.

Data Collection Summary:

Timing of Measurements

All survey variables were collected at one point in time.

Variables

Vegetarianism. Assessed with one question: “Are you on a special diet because of being a vegetarian?”
Eating behavior. Assessed with an 11-item food frequency questionnaire. Category responses included never or hardly ever, sometimes, once a day or more than once a day.
Disordered eating behavior. Assessed with four questions accounting for frequency of dieting, binge eating, self-induced vomiting and laxative use.
Health-compromising behaviors. Four variables were assessed, including frequency (on a six-point scale) of tobacco, alcohol and marijuana use; and past suicide attempts (yes or no).
Health-promoting behaviors. Frequency of exercise, tooth-brushing and seatbelt use was assessed.
Demographics. Parents' education level, parents' employment status, race or ethnicity, sex, age and self-reported height and weight were assessed.

Description of Actual Data Sample:

All adolescents who indicated they were vegetarians on the MAHS (n=107) were included in this study (approximately 0.6% of the original 17,544 adolescents who participated in the MAHS). A randomly matched comparison group of non-vegetarian youth participating in the MAHS (n=217) was matched case-by-case to the vegetarian group at a 2:1 ratio for sex, age and ethnicity.

As planned, the groups were similar to each other for the matched variables including sex, age and ethnicity.

Sex

19% male, 81% female.

Age

30% were 14 years of age or younger, 37% were 15 or 16 years and 27% were 17 years or older.

Ethnicity

88% white, 5% African American, 2% Hispanic, 2% Native American, 4% Asian American.

Other relevant demographics

There were no significant differences between vegetarian and non-vegetarian groups for socioeconomic characteristics and weight status.

Location

Non-urban Minnesota (outside of the Minneapolis-St Paul metropolitan area and Duluth).

Summary of Results:

Food Intake Pattern Differences Between Vegetarian (n=106) and Non-vegetarian (n=214) Adolescents

Except for grains and beans, peas and peanut butter, chi-square analyses revealed statistically significant differences for all other types of foods:

Fruits or fruit juice (Χ²=23.3; P<0.001):

Vegetarian (once a day=28) (more than once a day=56)
Non-vegetarians (once a day=36) (more than once a day=29)

Vegetables (Χ²=33.4; P<0.001):

Vegetarian (once a day=27) (more than once a day=53)
Non-vegetarians (once a day=44) (more than once a day=21)

Sweets or cakes(Χ²=29.4; P<0.001):

Vegetarian (once a day=23) (more than once a day=13)
Non-vegetarians (once a day=30) (more than once a day=36)

Salty snack foods (Χ²=19.0; P<0.001):

Vegetarian (once a day=16) (more than once a day=4)
Non-vegetarians (once a day=23) (more than once a day=16)

Dairy foods (Χ²=10.9; P<0.01):

Vegetarian (once a day=4) (more than once a day=75)
Non-vegetarians (once a day=2) (more than once a day=89)

Eggs (Χ²=17.3; P<0.001):

Vegetarian (once a day=7) (more than once a day=0)
Non-vegetarians (once a day=10) (more than once a day=1)

Red meat (Χ²=191.4; P<0.001):

Vegetarian (once a day=0) (more than once a day=0)
Non-vegetarians (once a day=40) (more than once a day=9)

Fish or poultry (Χ²=27.7; P<0.001):

Vegetarian (once a day=12) (more than once a day=3)
Non-vegetarians (once a day=9) (more than once a day=3)

As illustrated in Table 1, higher percentages of vegetarians adolescents reported engaging in disordered eating behaviors than non-vegetarians

Table 1

Variables	No. (%) of Vegetarians (n=107)	No. (%) of Non-vegetarians (n=214)	Χ²	P-value
Frequency dieting (>5 times per year)	41 (38)	45 (21)	10.9	<0.001
Binge eating (ever)	46 (44)	67 (32)	4.6	<0.05
Self-induced vomiting (ever)	16 (15)	8 (4)	13.2	<0.001
Laxative use (ever, for weight control)	8 (8)	2 (1)	10	<0.001

Health-compromising behaviors

There were no statistically differences between adolescent vegetarians and non-vegetarians for tobacco, alcohol or marijuana use, or reported past suicide attempts.

Health-promoting behaviors

There were no statistically significant differences between adolescent vegetarians and non-vegetarians for tooth brushing or physical activity. Seatbelt use (usually or always) was reported by significantly more vegetarians (64%) than non-vegetarians (44%) (Χ²=10.6, P<0.001).

Author Conclusion:

Compared with non-vegetarians, vegetarian adolescents were twice as likely to consume fruits or vegetables, one third as likely to consume sweets and one fourth as likely to eat salty snack foods more than once per day. Concerns about vegetarian diets included relatively low consumption patterns of foods high in protein, iron, zinc and calcium. Vegetarians were more likely to engage in all of the disordered eating patterns examined in the study, including frequent dieting, binge-eating, self-induced vomiting and laxative use. Health-care providers need to be alert to vegetarian adolescents’ higher risk for disordered eating patterns.

According to the authors, the randomly matched comparison group of non-vegetarians and the non-clinical, population-based sample are major strengths of this study because other previous studies have focused on clinical populations and used convenience samples. This study is limited by the restricted generalizability to youth in other geographic locations. Furthermore, measures used to assess vegetarianism were somewhat incomplete and brief and did not allow for a comprehensive assessment of food-item consumption.

Funding Source:

University/Hospital:

University of Minnesota, Minneapolis

Reviewer Comments:

The authors detail the major limitations of the study, which include limited generalizability to other adolescent populations and the lack of precision provided by the measures of vegetarianism and eating behaviors. Validity information related to the survey questions, including the dietary variables, are not provided. Despite these limitations, this secondary data analyses (with matched control subjects) was well-conducted, and the findings yield important information regarding vegetarianism among adolescents.

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)	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?	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)	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.)	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?	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%.)	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?	No
	4.3.	Were all enrolled subjects/patients (in the original sample) accounted for?	No
	4.4.	Were reasons for withdrawals similar across groups?	No
	4.4.	Were reasons for withdrawals similar across groups?	No
	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.)	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.)	N/A
	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?	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?	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?	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?	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)?	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?	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