Vegetarian Nutrition

VN: Types and Diversity of Vegetarian Diets (2009)

Citation:

Greenwood DC, Cade JE, Draper A, Barrett JH, Calvert C, Greenhalgh A. Seven unique food consumption patterns identified among women in the UK Women's Cohort Study. Eur J Clin Nutr. 2000 Apr; 54(4): 314-320.

PubMed ID: 10745282
 
Study Design:
Cross-Sectional Study
Class:
D - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:

To identify consumption patterns or habits that classify people according to the types of food they choose to consume, rather than based on self-definition or on the basis of nutrient intake alone.

Inclusion Criteria:

Women from the UK Women's Cohort Study.

Exclusion Criteria:

No apparent exclusion criteria within the UK Women's Cohort Study.

Description of Study Protocol:

Recruitment

Women for the UK Women's Cohort Study were identified from questionnaires sent between 1995 and 1998 to 61,000 potential subjects. Subjects were identified based on responses to a 217-item food frequency questionnaire (FFQ).

Design

The goal was to identify homogeneous clusters of individuals based on responses to the FFQ using cluster analysis techniques.

The authors then examined the relationships between each cluster and sociodemographic characteristics, indicators of health and diet, and nutrient intakes of the different clusters of women identified by the cluster analysis.

Blinding used

None.

Intervention

None.

Statistical Analysis

Cluster analysis was done using a k-means cluster algorithm. Robustness of the identified clusters was checked by trying different initial cluster centers and by using different rules of convergence. Other characteristics were then tested for association with the identified clusters by using non-parametric analysis of variance for continuous variables and chi-square tests for dichotomous variables.

Because of the large size of the cohort, the relationship between clusters and other characteristics were all statistically significant at P<0.001, even when the differences among clusters were of little practical importance.

Data Collection Summary:

Timing of Measurements

 Questionnaires were sent between 1995 and 1998.

Factors

  • Diet cluster: Based on results from a 127-item FFQ designed to capture food intake patterns over the previous 12-month period. The FFQ was adapted from the one used in the European Prospective Investigation into Cancer (EPIC) study
  • Food frequency: Measured on a 10-point scale from "never" to "six+ times per day"
  • Sociodemographic characteristics
  • Indicators of health and diet
  • Nutrient intakes.
Description of Actual Data Sample:

 

Initial N

61,000 questionnaires originally sent. 33,971 women were selected.

Attrition (final N)

NA.

Age

35 years to 69 years at recruitment; mean 52±9 years.

Ethnicity

Not reported.

Other relevant demographics

  • Generally well-educated (43% educated to "A" level standard or beyond)
  • Mean age leaving full-time education was 18±4 years
  • 55% held managerial, administrative, professional, technical or association professional positions
  • 30% described themselves as vegetarian
  • 58% take vitamins, minerals, fish oils, fiber or other food supplements (substantially higher than in the national population)
  • 11% were current smokers.

Anthropometrics

  • BMI mean 24.4±4.3 [compared to 24.8 (age 35-49) and 26.2 (age 50-64) among women in the national population]
  • 9% were obese (BMI ≥30)
  • Mean waist-to-hip ratio is 0.75±0.06.

Location

UK.

Summary of Results:

The authors identified seven natural clusters based on relatively high or low levels of consumption of particular foods. This served to define clusters based on diet diversity as well as consumption of types of foods.

Food Consumption Patterns

The authors identified cluster membership based on food consumption patterns, not on the subjects' self-definition. The seven clusters and the characteristic food types consumed are presented in Table 1.

Cluster

High-quantity foods

Moderate-quantity foods

Low-quantity foods

1. Monotonous low-quantity omnivores

White bread, milk, sugar

Potatoes, meat

Most other foods, especially bran and whole-meal food, soy products, yogurt, nuts, pulses, fruit and vegetables, alcohol

2. Health-conscious omnivores

Bran, potatoes, whole-meal food, yogurt, low-fat dairy products, pulses, fish, vegetables, salad, fruit

Most other foods including meat and wine

Chips, sugar

3. Traditional meat, chips and pudding eaters

White bread, chips, meat, sugar, high-fat and creamy food, biscuits, cakes

Most other foods including alcohol

Whole-meal food, soy products, vegetables, salad, fruit

4. Higher diversity, traditional omnivores

Chips, white pasta and rice, high-fat and creamy food, eggs, meat, fish, chocolate, biscuits, crisps. More fish and salad than cluster 3. More diversity than cluster 3

Vegetables, fruit, alcohol

Less cakes and puddings than cluster 3

5. Conservative omnivores

None reported

Most food, including potatoes, meat, fish, eggs, fruit, vegetables

Cereals, chips, whole-meal food, nuts, pulses, spreads and dressings, chocolate, crisps, biscuits. Less red meat, less chips and less puddings than clusters 3 and 4.

6. Low-diversity vegetarians

Whole-meal bread, soy products, pulses, fruit (apart from exotic fruit) vegetables

Cereals


 

7. High-diversity vegetarians

Whole-meal bread, cereals, whole-meal pasta and rice, soy products, spreads, nuts, pulses, vegetables, fruit herbal tea (generally higher consumption of these products than low diversity vegetarians)

None reported


 

The authors point out that it is not just the food type chosen, but the diversity of foods eaten that help define the clusters. In the case of the two vegetarian groups, it is the range of different foods eaten, and not just the frequency of specific food items, that differentiates the two groups.

Defining a Vegetarian: Self-Description Vs. Empirical Identification

The authors find that some women who identify themselves as vegetarian fell within the non-vegetarian clusters based on their actual consumption patterns. Similarly, some women who defined themselves as non-vegetarian fell into the vegetarian clusters.

How did this happen?

Vegetarians” in the Non-Vegetarian Group

Even though some women define themselves as vegetarian, their food consumption patters are more similar to women in the non-vegetarian clusters. The authors found that:

  • 59% of self-described vegetarians who fell into a non-vegetarian group eat meat (most of which is fish)

  • 12% of “vegetarians” in the non-vegetarian group eat red meat, although less frequently that self-described non-vegetarians in the non-vegetarian groups [0.02 portions per day compared to 0.87 portions per day (P<0.001)]

Women who call themselves vegetarians may have food-intake patterns more similar to non-vegetarians in terms of overall food intake and diversity, but reduce or cut out red meat. It may be the way that the individual thinks about their red meat intake (rather than their actual red meat intake) that leads them to define themselves as vegetarian.

Non-Vegetarians” in the Vegetarian Group

Non-vegetarians in the two vegetarian groups have overall food consumption patterns more like vegetarians than members of any of the three non-vegetarian groups. The authors surmise that this group may follow a vegetarian diet as far as possible, but occasionally allow themselves fish.

It may be for these women who describe themselves as non-vegetarian that the presence of any meat in their diet immediately disqualifies them as vegetarian.

 

How Do Groups Compare of Various Health and Dietary Characteristics?

The authors describe the dietary and health characteristics of the different clusters. Even though they fall into an omnivore category, health-conscious omnivores were more likely to consume at least five portions of fruits and vegetables per day as well as spend more time vigorously exercising then members of the two vegetarian groups. Also, fully one fifth of the members of the monotonous low-quantity omnivore group described themselves as vegetarians.

Cluster

Describes herself as vegetarian

Uses food supplements

Consumes five portions of fruits and vegetables per day

Median time in vigorous physical exercise (minutes per week)

Monotonous low-quantity omnivores

20%

53%

5%

0

Health-conscious omnivores

35%

65%

30%

70

Traditional meat, chips and pudding eaters

3%

50%

4%

20

Higher diversity, traditional omnivores

5%

55%

12%

60

Conservative omnivores

16%

56%

14%

30

Low-diversity vegetarians

71%

66%

12%

60

High-diversity vegetarians

75%

69%

23%

60

In terms of practical import, the authors point out that

  • Not all diets that are healthful in one respect are healthful in all respects (for example, a higher fat diet may also be high in fruits and vegetables)

  • There are complex interactions between nutrients, other dietary constituents, and the processing and preparation of foods that influence the health effects of diets.

 

Author Conclusion:

Classifying diets in more pragmatic terms than just nutrient intake should provide valuable insight to complex diet-disease relationships. Dietary advice, although based on nutrient content of meals, needs to take account of the combinations of different food types that people naturally choose to use together.

Funding Source:
Not-for-profit
0
Foundation associated with industry:
Reviewer Comments:

Strengths

  • Well-designed and executed study
  • Authors were thorough in reporting the limitations of the study.

Weaknesses

The sample was demonstrably different than the larger population on several factors--most important of which may be the level of health consciousness, income and education. It is unclear how the clusters identified in the sample might change if a representative sample from the larger population was examined.

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.) 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? 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? 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? N/A
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? N/A
  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? 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? 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? 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? 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? Yes
  7.6. Were other factors accounted for (measured) that could affect outcomes? Yes
  7.7. Were the measurements conducted consistently across groups? N/A
  7.7. Were the measurements conducted consistently across groups? N/A
  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)? 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? 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? 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