Vegetarian Nutrition

VN: Cardiovascular Disease (2008)

Citation:

Toohey ML, Harris MA, Williams D, et al. Cardiovascular Disease Risk Factors are Lower in African-American Vegans Compared to Lacto-Ovo-vegetarians. Journal of the American College of Nutrition. Vol 17 (5), 425-434, 1998.

 
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 examine blood pressure and blood lipids in a sample of black Seventh-Day Adventist vegans and ovlactovegetarians
  • In addition, the plasma concentrations of ascorbic acid and malondialdehyde equivalents were measured to determine if plasma ascorbic acid concentrations could explain any differences in cardiovascular disease risk factors between African-American ovolactovegetarians and vegans.
Inclusion Criteria:
  • Vegan
  • Ovolactovegetarian
  • African-American.
Exclusion Criteria:
  • Regular consumption of meat, fish or poultry
  • Incompletion of questionnaire.
Description of Study Protocol:
  • Recruitment: Researchers contacted church leaders of Seventh-Day Adventist Churches in three citites: Washington D.C., Philadelphia and Baltimore.
  • Design: Cross-sectional epidemiological investigation.

Statistical Analysis

  • Two-way ANOVA: Main effects of diet and gender and any interactions
  • Simple correlation analyses: To identify associations among plasma AA, plasma MDA and specific CVD risk factors
  • Step-wise multiple regression analyses: To identify the independent variables to identify the most variance in blood pressure and blood lipid values
  • Significance: P<0.05.
Data Collection Summary:

Timing of Measurements

One time measurement.

Dependent Variables

  • Blood pressure
  • STC (mmol per L)
  • LDL-cholesterol (mmol per L)
  • HDL-cholesterol (mmol per L)
  • TG (mmol per L)
  • STC/HDL-cholesterol
  • LDL-cholesterol/HDL-cholesterol.

Independent Variables

  • Plasma AA
  • Malondialdehyde (MDA) equivalents (used to estimate the magnitude of lipid peroxidation)
  • Height without shoes, body weight without shoes, body mass index (BMI) and circumferences were measured in subjects
  • The waist-to-hip circumference ratio (WHR) and the waist-to-thigh circumference ratio (WTR)
  • Following a five-minute seated rest, two resting BP measurements were taken (spaced two minutes apart)
  • Demographic characteristics, personal and family health history and personal health (habits, health habits and history questionnaire)
  • Usual consumption of 141 different foods and related food items during the previous three months (food frequency questionnaire).

Control Variables

  • Sex
  • Age
  • Waist-to-thigh circumference ratio.
Description of Actual Data Sample:

Initial N

  • Male vegans: 14 years
  • Male ovolactovegetarians: 49 years
  • Female vegans: 31 years
  • Female ovolactovegetarians: 94 years.

Age

  • Male vegans: 45.6 years
  • Male ovolactovegetarians: 49.8 years
  • Female vegans: 51.1 years
  • Female ovolactovegetarians: 52.1 years.

Ethnicity

African-American.

Other Relevant Demographics

Seventh-Day Adventist.

Location

  • Washington, DC
  • Philadelphia, PA
  • Baltimore, MD.
Summary of Results:

Anthropometric Findings

The ovolactovegetarians had been members of the Seventh-Day Adventist church for a significantly longer period of time than the vegans (P<0.001).

Weight

  • Ovolactovegetarians weighed more than the vegans (P<0.05)
  • Body mass index (BMI) did not differ between sexes, however the vegans exhibited a lower mean BMI value than the ovolactovegetarians (P<0.03)
  • The vegans also exhibited significantly (P<0.04) lower measurement values for thigh circumference and waist-to-hip ratio, compared to the ovolactovegetarians
  • There was a diet-by-sex interaction for waist-to-hip ratio measurements, with male ovolactovegetarians having higher values than either of the other three groups (P<0.02).

Nutrient Intake

Macronutrients

  • Compared to ovolactovegetarians, vegans consumed significantly more (all P<0.05 or lower):
    • Carbohydrates
    • Fiber intake, relative to energy intake
    • Higher ratio of polyunsaturated fatty acids to saturated fatty acids (P:S ratio).
  • Compared to ovolactovegetarians, vegans consumed significantly less (all P<0.05 or lower):
    • Total and saturated fat
    • Cholesterol.

Micronutrients

  • Vegans had a significantly higher daily intake of AA, although intake of both groups was greater than the Recommended Daily Amount (RDA) (60mg per day)
  • After standardizing for energy intake, vegans had higher intakes (all P<0.05 or lower) of:
    • Vitamin A
    • Alpha-tocopherol
    • Thiamin
    • Vitamin B6
    • Folate
    • Potassium
    • Magnesium
    • Iron
    • Zinc
    • Chromium.
  • Vegans consumed less:
    • Sodium
    • Vitamin D
    • Vitamin B12
    • Calcium.

Blood Pressure and Blood Lipids

Blood Presssure

  • No systolic or diastolic BP differences between vegans and ovolactovegetarians
  • The mean BP values were in the normotensive range for both groups.

Blood Lipids

  • Findings adjusted for age and waist-to-hip ratio
  • Blood lipid values were low for all four groups, with vegans exhibiting significantly (P<0.05) lower concentrations of:
    • STC
    • LDL-cholesterol
    • Triglycerides
    • Serum total cholesterol
    • HDL-cholesterol (STC:HDL-C).
  • For HDL-cholesterol, females had higher mean (P=0.04) values than males.

Plasma AA and MDA Associations

  • There were significant inverse correlations (-0.45, P<0.001) between plasma AA levels and both systolic and diastolic BP
  • Despite the higher intake of AA among the vegans, there were no significant group differences in plasma AA, nor was AA intake related to plasma AA
  • The correlation for MDA and BP was of similar magnitude (0.45, P<0.001), but was in the opposite direction
  • Age was the strongest correlated variable with both systolic and diastolic BP. Fat patterning was typically correlated with CVD risk factors at least as strongly as was body mass index. The dietary P:S ratio was correlated (inversely) with STC and LDL-cholesterol.

Multivariate Analysis

  • Systolic BP
    • Age, AA and MDA together explained 53% of the variability in SBP for the entire sample, with age accounting for most of the variability (F=122.05, P<0.0001), followed by AA (F=33.99, P<0.0001) and MDA (F=10.21, P<0.002), as independent predictors.
  • Diastolic BP
    • For DBP, plasma AA emerged as the greatest independent predictor (F=17.84, P<0.0001), followed by protein (energy percentage; F=8.52, P<0.01) and waist circumference (F=6.61, P<0.004)
    • These variables explained 16% of the variability in the multiple-regression model.
  • Blood Lipids
    • In the multiple-regression analyses, age and anthropometric measures (i.e., BMI, waist circumference, WHR) were the best predictors of the blood lipids
    • Dietary fiber was inversely related to several blood lipid variables and emerged as a significant independent contributor to the prediction of triglycerides and the ratios of STC to HDL-cholesterol and LDL-cholesterol to HDL-cholesterol
    • Neither MDA nor AA were independently related to any of the blood lipid concentrations.
  • Normotensive and Hypertensive Subjects
    • Plasma AA was significantly lower (P<0.0001) for those in hypertension (N=32, 52.2±7.9mmol per L) than normotensive subjects.
Author Conclusion:
  • Seventh-Day Adventist African-American vegans, compared to ovolactovegetarians, exhibited significantly higher intakes of nutrients that are associated with reduced risk for CVD, including fiber, AA, alpha-tocopherol, potassium, magnesium, vitamin B6 and folate and lower intakes of sodium
  • They also ingested less total and saturated fat and exhibited lower levels of several lipid parameters, including STC, LDL-cholesterol, triglycerides and STC-to-HDL-cholesterol
  • While there were no blood pressure differences between dietary groups, both SBP and DBP were inversely correlated with plasma AA and positively correlated with MDA equivalents within the entire sample
  • Future research should examine the possibility that a plant-based diet not only improves the lipid profile in African-Americans, but also reduces their risk of CVD.
Funding Source:
University/Hospital: Colorado State University
Reviewer Comments:

No adjustments made for medication or lifestyle factors related to cardiovascular disease, including sedentary lifestyle and smoking.

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? Yes
  2.4. Were the subjects/patients a representative sample of the relevant population? Yes
  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) Yes
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) Yes
  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.) 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.) 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? No
4. Was method of handling withdrawals described? No
  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%.) No
  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%.) No
  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? ???
  4.4. Were reasons for withdrawals similar across groups? ???
  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? No
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? No
  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? No
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? No
  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? No
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? No
  6.6. Were extra or unplanned treatments described? No
  6.6. Were extra or unplanned treatments described? No
  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? No
7. Were outcomes clearly defined and the measurements valid and reliable? No
  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? No
  7.2. Were nutrition measures appropriate to question and outcomes of concern? No
  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? N/A
  7.5. Was the measurement of effect at an appropriate level of precision? N/A
  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)? 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)? Yes
  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? No
  10.1. Were sources of funding and investigators' affiliations described? No
  10.2. Was the study free from apparent conflict of interest? Yes
  10.2. Was the study free from apparent conflict of interest? Yes