Vegetarian Nutrition

VN: Types and Diversity of Vegetarian Diets (2009)

Citation:

Nardoto GB, Silva S, Kendall C, Ehleringer JR, Chesson LA, Ferraz ES, Moreira MZ, Ometto JP, Martinelli LA. Geographical patterns of human diet derived from stable-isotope analysis of fingernails. Am J Phys Anthropol. 2006 Sep; 131 (1): 137-146.

PubMed ID: 16552735
 
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 determine whether regional differences persist even though the current global economic structure provides access to different food products in an unprecedented way.

Inclusion Criteria:

Adults.

Exclusion Criteria:

None reported.

Description of Study Protocol:
  • Recruitment: Recruitment method was not described
  • Design: Cross-sectional design
  • Blinding used: None
  • Intervention: Not applicable
  • Statistical analysis:
    • Student's T-test was used testing independent samples of omnivores and vegetarians
    • Differences among geographical regions were tested using one-way analysis of variance (with post hoc Tukey test)
    • Cluster analysis was used for analyzing questionnaire data.
Data Collection Summary:
  • Timing of recruitment: Individuals were recruited between September 2000 and September 2004
  • Dependent variables: Stable-isotope content of fingernails (δ13C and δ15N)
  • Independent variables:
    • Food items available in regions (from questionnaire given to restaurants and supermarkets, as well as collection of locally producted food items). Foods were analyzed using stable-isotope ratio analysis.
    • Individual food intake (gathered from a brief questionnaire providing general details of diet)
    • Subjects were categorized as ovo-lacto-vegetarians or omnivores based on answers to the questionnaire 
  • Confounding variables: Sex and age.
Description of Actual Data Sample:
  • Initial N: Number of individuals:
    • 273 from Southeast Brazil
    • 22 from Sanarém, Pará, Brazil (city)
    • 15 from Sao Jorge, Brazil (forest)
    • Six from Jamaraquá (river)
    • 10 from Socoro (lake)
    • 490 from the US
    • 35 from five countries in Western Europe
  • Attrition (final N): Not available
  • Age: Adult
  • Ethnicity: Not reported
  • Other relevant demographics: "Mostly" middle class
  • Anthropometrics: Not reported
  • Location: Brazil, US and Europe.

 

Summary of Results:

Food access is becoming increasingly global. Foods once available only in one part of the world are becoming increasingly accessible in far-flung parts of the globe. We might think that the creation of a global food system (what the authors call the “global supermarket) would increase the diversity of foods available and so decrease regional differences in foods and the physiological effects of foods.

In short, vegetarians in Brazil should resemble vegetarians in the US more and more. The same pattern should also hold for omnivores if the “global supermarket” idea is correct.

But, is this what we see?

The authors say that regional differences persist in diet even though access to foods from different parts of the globe has increased. They measure stable-isotope ratios (d15N and d13C) in individual's fingernails to determine whether region still makes a difference.

If region still makes a difference, we should see not only a difference between vegetarians and omnivores in terms of isotope content of fingernails, but we should also see a difference between regions even when people are on the same type of diet (e.g., vegetarians in the US will be different than vegetarians in Brazil).

First, Do We See Differences in Stable-Isotope Content of Fingernails?

Omnivores

The authors compared US (Salt Lake City, UT) populations with populations from South Eastern Brazil (with large urban centers) and Western Europe. They found no significant difference between males and females or differences by age.

  • SE-Brazil had higher d13C and d15N values (-15.4±1.0, 10.4±0.7) than Western USA (-18.8±0.8 and 9.4±0.6) and W-Europe (-20.2±1.2 and 9.6±0.8) (P<0.05).

  • US values were higher than Western European values.

So, in terms of omnivores, we do see a regional difference.

Omnivores Vs. Vegetarians

Among vegetarians, SE-Brazil was higher in d13C and d15N than individuals from Western US (P<0.05)

In Brazil

  • In vegetarian/omnivore comparison, no statistical difference in value in d15N

  • d13C value in vegetarians significantly lower than that of omnivores in Brazil (P<0.05).

In US

  • Vegetarians had d15N values that were significantly lower (P<0.05) than omnivores in Western US

  • US vegetarians and omnivores were not significantly different in their d13C values.

So, not only were vegetarians in Brazil different than vegetarians in the US (Brazilians higher for both isotopes), but the ways in which vegetarians were different than omnivores in the respective countries were different.

Could Differences in Isotope Content Be Due to Differences in Foods?

In Brazil

  • Beef and sugar, followed by cereal and diary-derived products were more closely related to d13C than d15N in omnivores

  • Fruits, vegetables and grains in the diet were more closely related to d15N than d13C in omnivores

  • These patterns were the same in Brazilian vegetarians (excluding meat).

In the US

  • Dairy-derived products, meat, fruit and vegetables more closely related to d15N than d13C in omnivores

  • Cereals were more closely related to d13C values in omnivores

  • These patterns were the same in US vegetarians (excluding meat).

In short, isotope content in fingernails was associated with different foods in different regions.

Why Might We See These Differences?

So, we see that not only are vegetarians and omnivores different, but that regions are different. Additionally, we see that the differences between vegetarians and omnivores are not the same in different regions.

Why?

Differences Among Food Types

The authors test for differences among food types to see whether this may explain regional differences. They classify different types of foods into four main categories:

  1. C3 plants (C3 cereals—barley, oats, rice, wheat—tuber, vegetables, fruit)

  2. C4 plants (C4 cereals—maize, and others)

  3. Animal and products

  4. Seafood

They tested to see whether there was a difference among these four categories (for instance, is there a difference between C3 foods and C4 foods?) They found that there was a significant difference in the d13C and d15N values as they relate to fingernail isotope content across categories.

Differences Within Food Groups

The authors then tested to see whether there was a difference within each category in different regions (for instance, were C3 plant foods in Brazil different than C3 plant foods in the US?).

They also found significant differences between Brazil and the US i terms of the d15N content of C3 cereals, tubers and fruits. Brazil showed heavier d15N values than the US by 0.9% to 6.2%. Also, it appeared that, overall, US values showed less variation in d15N values within these foods. In short, not only were Brazilian foods in this category higher than US foods, but there was also a wider range of these values in Brazilian foods. US C3 cereals, tubers and fruits had a more restricted range of d15N levels.

The authors also found a significant difference in dN15 values in animal products between Brazil and the US as well.

What Explains Regional Differences? Why Isn't a Tuber Just a Tuber?

The authors then go on to examine why there would be differences between plants of the same type and the same types of meats in the different regions.

  • C3 plants in Brazil are higher in d15N than some of the same plants in the US. This caused the d15N levels in Brazilian vegetarians to be closer to that of US omnivores. Also, Brazilians eat more of C3 plants while individuals in the US consume more C4 plants (which helps explain the higher levels of d13C levels in the SE Brazilian population).

  • But why would C3 plants in Brazil be higher than in the US? The authors suggest that part of the explanation could be differences in the use of synthetic fertilizers. Using synthetic fertilizers on plants (both for human and animal consumption) decreases the d15N content. The US uses about six times more synthetic fertilizer than Brazil.

In short, some physiological differences among vegetarians may vary by region because:

  • While vegetarians in different regions exclude meat from their diet, they eat different types of plant foods (e.g., more C3 or C4 plant foods)

  • The same plant foods may be different in different regions because of the plants are grown in different ways (using synthetic fertilizers or not).

With regard to meat products, some part of the variation between regions can be due to the differences in the plants fed to the animals (e.g., grains grown with synthetic fertilizers in the US). Differences in plant foods create differences in terrestrial animal foods.

Urban and Rural

Of course, regional variation does not explain everything. The authors suggest that as food accessibility becomes more global (foods that used to be available only in one part of the globe now being available across the globe) we should still see differences between areas that are more urban (and have greater access to a wider variety of foods) and those that are less integrated into the global food system. In fact, this is what they find. Comparing different regions in Brazil, the authors report that the isotope composition of fingernails in urban centers in SE Brazil was quite different than those of more isolated communities in the Amazonian region.

Author Conclusion:
  • Despite increased access to food because of the development of a "global supermarket," regional differences between Southeastern Brazil and the Western US persist when measured in terms of fingernail stable-isotope content. These differences appear to be associated with regional agricultural and animal production practices.
  • Carbon and nitrogen isotopes of human fingernails hold dietary information directly related to both food sources and dietary practices in a region.
Funding Source:
University/Hospital: Centro de Energia Nuclear na Agricultura - Univ of Sao Paulo
Reviewer Comments:

Very detailed description of the methods of stable-isotope ratio analysis, but very weak description of sampling design.

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? 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? No
  2.2. Were criteria applied equally to all study groups? No
  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? No
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? No
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) No
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) 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
  3.4. 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? 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.) 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? 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? 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? No
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? No
  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? N/A
  7.1. Were primary and secondary endpoints described and relevant to the question? N/A
  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? 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? No
  8.6. Was clinical significance as well as statistical significance reported? No
  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