Vegetarian Nutrition

VN: Adolescence (2009)

Citation:

Donovan UM, Gibson RS. Dietary intakes of adolescent females consuming vegetarian, semi-vegetarian, and omnivorous diets. J Adolesc Health. 1996 Apr; 18(4): 292-300.

PubMed ID: 8860794
 
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 study targeting Canadian adolescent females was to compare the nutrient and food intake patterns among ovolactovegetarians, semi-vegetarians and omnivores.

Inclusion Criteria:

Inclusion criteria include females between 14 years and 19 years of age.

Exclusion Criteria:

No exclusion criteria were specified.

Description of Study Protocol:

Recruitment

Participants were recruited for the study via media announcements at natural health food stores, high schools, universities and in other high-visibility areas. Respondents were classified into three categories based on their food consumption patterns as assessed by a food frequency questionnaire.

Design

Cross-sectional.

Statistical Analysis

Analysis of variance tests were used to examine differences among the three dietary groups; Tukey HSD test statistic was used in post-hoc comparisons. Kruskal-Wallis test was used to determine differences in contributions of major food groups to nutrient intakes and among anthropometric measurements. Fisher’s exact test was used to examine frequency distributions of weight-for-age and weight-for-height. 

Data Collection Summary:

Timing of Measurements

Dietary data were collected using weighted food records completed by the subjects on three consecutive days, including one weekend day. Health and lifestyle questionnaires were collected via personal interviews.  Methods for collecting anthropometric data are not reported (reference provided for previous publication).

Variables

  • Diet group: Diet groups were defined according to food intake (rather than self-report):
    • Ovolactovegetarian: Consumed red meat, poultry and fish less than once per month, but included dairy or egg products,
    • Semi-vegetarian: Consumed red meat less than once per month, but included poultry or fish more than once per month
    • Omnivore: Consumed a mixed diet.
  • Energy
  • Macronutrients: Fat, protein and carbohydrates
  • Micronutrients: Calcium, phosphorous, iron, zinc, thiamin, riboflavin, niacin, vitamin C, copper, manganese
  • Food groups: Dairy products; eggs; legumes and nuts; meat, poultry and fish; cereal products; fruits and vegetables; miscellaneous
  • Weight-for-age percentiles
  • Weight-for-height percentiles
  • Duration of and reasons for dietary patterns.
Description of Actual Data Sample:

Sample (N): A total of 122 females, including 78 ovolactovegetarian, 15 semi-vegetarians and 29 omnivores participated in the study

Age: Age range 14 years to 19 years; mean age 17.9±1.5 years

Ethnicity: Ethnicity and other demographics are not provided

Anthropometrics: Of the total participants, seven had weight-for-age less than the 15th percentile and 18 had weight-for-height less than the 15th percentile. All others were within the normal range of 15th to 85th percentile. Anthropometric differences among groups were not reported.

Location: Southern Ontario, Canada.

Summary of Results:

Energy and Nutrient Intake Differences Among Ovolactovegetarians, Semi-Vegetarians and Omnivores

Table 1 illustrates that energy, percentage of energy from macronutrients and macronutrients were similar across groups, with the exception of percentage of energy from protein and dietary fiber. Micronutrients that varied significantly across groups are also presented in Table 1.  Mean nutrient intakes were similiar across groups for all other nutrients including calcium, phosphorus, iron, zinc, thiamin, riboflavin and vitamin C.

Table 1:  Mean Energy and Nutrient Intakes Among Ovolactovegetarians, Semi-Vegetarians and Omnivores

Nutrient

Ovolactovegetarian (n=78)

Semi-Vegetarian (n=15)

Omnivore (n=29)

 

Mean±SD Mean±SD Mean±SD
Energy (kJ) 7,164±1,944 7,157± 2,599 7,286±1,733
Percentage energy from fat 33±6 30±9 32±7
Percentage energy from protein 12±3* 13±3 13±3*
Percentage energy from carbohydrate 58±7 59±11 55±8
Protein (g) 51±16 54±23 58±19
Fat (g) 63±21 56±23 63±21
Dietary fiber as non-starch polysaccharide (NSP) (g) 14±6*  13±6  10±4*
Copper (mg)  1.4±0.5*  1.2±0.5  1.1±0.3*
Manganese (mg)  4.1±1.8*  3.2±1.9  2.8±1.2*
Niacin (NE)  21.5±7.8*  24.5±10.5  27.3±10.2*

*Values within rows are significantly different (P<0.01) 

Comparing Dietary Patterns of Ovolactovegetarians, Semi-Vegetarians and Omnivores to Canadian Recommended Intakes

  • In all three groups, mean intakes of energy, iron and zinc were less than Canadian recommendations and calcium, phosphorous, vitamin C and B vitamins were more than Canadian recommendations
  • Of the three groups, more semi-vegetarians had intakes below Canadian recommendations for energy, protein, iron, zinc, riboflavin and vitamin C.

Comparing Major Food Group Contributions to the Energy and Nutrient Intake Profiles Among Ovolactovegetarians, Semi-Vegetarians and Omnivores

  • Among all three groups, breads and cereals were the primary sources of energy, protein, fat, NSP, phosphorous, iron, zinc, copper, manganese, thiamin, riboflavin and niacin.  Dairy products were the primary source of calcium; fruits and vegetables were the primary source of vitamin C.
  • As illustrated in Table 2, several differences existed among groups for the daily intake of food groups. In summary, ovolactovegetarians consumed less dairy products, meat, poultry, fish and sweets, and more legumes and nuts and vegetables than did omnivores (P<0.02). 

 Table 2. Mean Contribution from Food Groups Among Ovolactovegetarians, Semi-Vegetarians and Omnivores

Nutrient

Ovolactovegetarian (n=78)

Semi-Vegetarian (n=15)

Omnivore (n=29)

 

Mean±SD Mean±SD Mean±SD
Dairy products (g) 221±182a 327±212b 315±180b
Meat, poultry, fish and eggs (g) 8±9a 36±22b 73±57c
Legumes and nuts (g) 78±73a 45±55 12±19b
Cereal products (g) 282±116 288±149 304±142
Fruits (g) 341±246 403 ±338 292±199
Vegetables (g) 242±147a 159±121b 108±80b
Fats and oils (g) 16±12a  11±9b  11±10b
Sweets (g)  149±190  129±118  214±161

a,b,c Values within rows with different letters are significantly different (P<0.01) 

Contributions of food groups to nutrient intake were also examined and revealed the following:

  • Ovolactovegetarians received a higher proportion of all nutrients (P<0.05) from legumes and nuts; and more protein, NSP, calcium, iron, zinc, phosphorous, copper, vitamin C, thiamin, riboflavin and niacin (P<0.05) from fruits and vegetables
  • Omnivores received a higher proportion of all nutrients (P<0.05) (except NSP, calcium, and manganese) from meat, poultry and fish; and more NSP, iron, copper, thiamin, riboflavin and vitamin C from cereal products
  • Semi-vegetarians received more (P<0.05) copper, manganese and vitamin C from milk products.

Reasons for Dietary Patterns

The ovolactovegetarians and semi-vegetarians consisted of 33 Seventh Day Adventist (35%) and 60 (65%) “new” vegetarians. The Seventh Day Adventists were primarily motivated by religious and health reasons, whereas the “new” vegetarians were motivated by ethical and environmental considerations.

Author Conclusion:

More than 80% of the adolescents reported average intakes less than the average energy requirement for adolescent females, making it difficult to achieve adequate intakes of essential nutrients. 

  • For all groups, cereals were the major source of energy and most nutrients
  • Unlike earlier studies with adults, fat intake was not significantly less among vegetarians groups as compared with omnivores
  • Approximately one third of vegetarians and one fourth of omnivores had less-than-optimal protein intake
  • Mean fiber intake as non-starch polysaccharides was higher among vegetarians than among omnivores. 

Several important differences exist among groups for mineral and vitamin intakes. Prevalence of inadequate calcium, iron and zinc was high, especially in the ovolactovegetarian and semi-vegetarian groups, whereas intakes of phosphorus, thiamin, riboflavin, niacin and vitamin C were generally satisfactory. The adolescents tended to follow vegetarianism for humanitarian rather than health reasons. 

Funding Source:
Industry:
Kellogg Canada Ltd
Food Company:
Not-for-profit
Natural Sciences and Engineering Research Council of Canada
Reviewer Comments:

Unclear if convenience sample is representative of target population. Three-day weighted food record is a valid dietary assessment approach. Overall, very thorough analysis. However, there was a disconnect between the methods/statistical analysis section and the provided results. For example, no results provided for differences in frequency distributions of weight-for-age and weight-for-height. Furthermore, findings from the Nutrition Canada Survey (NC) conducted in the 1970s are illustrated and compared to findings in this study, but the NC study is not described in the analysis. Study limitations are not discussed.

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? 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? ???
  2.4. Were the subjects/patients a representative sample of the relevant population? ???
  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? ???
  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? ???
  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? 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? Yes
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? N/A
  4.4. Were reasons for withdrawals similar across groups? N/A
  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? ???
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? ???
  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.) ???
  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.) ???
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? ???
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? ???
  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? N/A
  8.1. Were statistical analyses adequately described and the results reported appropriately? N/A
  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? No
9. Are conclusions supported by results with biases and limitations taken into consideration? No
  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