Vegetarian Nutrition

VN: Types and Diversity of Vegetarian Diets (2009)

Citation:

Melby CL, Toohey ML, Cebrick J. Blood pressure and blood lipids among vegetarian, semivegetarian, and nonvegetarian African Americans. Am J Clin Nutr. 1994; 59: 103-109.

PubMed ID: 8279389
 
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:

The purpose of this study was to examine blood pressure (BP) and blood lipids among vegetarian, semi-vegetarian and non-vegetarian African-Americans.

Inclusion Criteria:

Black members of the Seventh-Day Adventist Church who attended regional meetings in Denver and Dallas and who were willing to participate in a health habits and health risk study.

Exclusion Criteria:

No exclusion criteria was noted in this report

Description of Study Protocol:

Recruitment and Sample Description

Black African-American members of the Seventh-Day Adventist Church, attending the Dallas or Denver regional meetings, were asked in writing and by verbal anouncement to participate in the study. Special effort was taken to encourage all church members to participate; not only elderly members or those with hypertension who might be more likely to participate.

  • 50% of conferees at each site volunteered, for a total of 167 individuals
  • Three-to-one female-to-male ratio of the sample replicated that of the overall population of conferees
  • Subjects self-categorized into one of three groups: Vegetarian, semi-vegetarian and non-vegetarian.

Design

Cross-sectional study:

  • Health habits and health history questionnaire (to determine VEG, SEMIVEG, or NONVEG)
  • Food frequency questionnaire (previous three months)
  • Blood pressure taken
  • Anthropometric measures: Height, weight, waist, hip and thigh circumferences, tricep skinfold measurement and waist-to-hip ratio, as well as waist-to-thigh ratio (to determine fat patterning)
  • Venous blood samples: Triglycerides, total and HDL-cholesterol, glucose and LDL-cholesterol.

Blinding Used

Investigators were blind to the individuals' dietary group assignment when measurements were performed.

Intervention

N/A.

Statistical Analysis

  • Descriptive statistics were computed to characterize the entire sample and the dietary groups as well as the distributions of independent and dependent variables
  • Group differences in BP and blood lipids were tested using analysis of variance (ANOVA), with group comparisons performed with Tukey's post-hoc test
  • Adjusted means of outcome variables were computed using the analysis of covariance (ANCOVA) with post-hoc comparisons using the least-significant-differences test
  • Simple and multiple-regression analyses were performed to identify the subject characteristics that were best able to explain variance of BP and blood lipids within the entire sample
  • Statistical significance was set at P<0.05; all values expressed as mean ±SEM.
Data Collection Summary:

Timing of Measurements

Not reported.

Dependent Variables

  • Blood pressure
  • Blood lipids: Triglycerides, total serum cholesterol, HDL cholesterol, LDL cholesterol and glucose.

Independent Variables

  • Vegetarian status: Via subject self-classification; VEG defined as no consumption of meat, fish or poultry
  • Semi-vegetarian: Via subject self-classification; SEMIVEG defined as consumption of flesh foods one to three times per week
  • Non-vegetarian status: Via subject self-classification; NONVEG defined as consumption of flesh foods daily.

Control Variables

N/A.

Description of Actual Data Sample:
  • Initial N: 167
    • Vegetarian (VEG): 66 total (46 female, 20 male)
    • Semi-vegetarian (SEMIVEG): 56 total (43 female, 13 male)
    • Non-vegetarian (NONVEG): 45 total (34 female, 11 male).
  • Attrition (final N): N/A
  • Age: Mean age of three groups was between 46 and 49
  • Ethnicity: Black African-Americans
  • Other relevant demographics: Mean length of church membership was 23.4 years
  • Anthropometrics: Mean values and distributions for the demographic, anthropometric and dietary characteristics were similar at the two sites, so the data were combined
  • Location: Denver and Dallas.
Summary of Results:

Physical Characteristics

  • Vegetarians weighed less than semi-vegetarians (P<0.05), but were not different from non-vegetarians
  • Vegetarians had significantly lower mean waist circumference and waist-to-hip ratio than other groups
  • No significant differences in any anthropometric characteristics between semi-vegetarians and non-vegetarians.

Physical Characteristics of the Three Dietary Groups of Black Adults

  Vegetarian
N=66
Semi-Vegetarian
N=56
Non-Vegetarian
N=45
Age (Years) 46.5±1.6 48.9±1.8 47.4±2.5
Height (cm) 167.6±1.2 167.8±1.1 166.6±1.3
Weight (kg) 74.7±2.1a 81.9±1.9b 79.4±2.3
BMI (kg/m2) 26.8±0.8 29.2±0.8 28.6±0.8
Waist (cm) 83.4±1.7a 90.4±1.8b 89.4±2.0b
Hip (cm) 104.3±1.8a 110.5±1.7b 108.8±1.7
Thigh (cm) 59.9±1.3 63.2±1.9 62.5±1.3
Waist:Hip 0.79±0.009a 0.82±0.009b 0.82±0.01b
Waist:Thigh 1.38±0.03 1.44±0.03 1.44±0.03
Ticeps-Skinfold Thickness (mm) 31.7±2.1 32.9±2.0 36.3±2.6

Not sharing a common superscript letter indicates not significantly different from each other, P<0.05.

Food Consumption Characteristics

  • Vegetarians had lower intakes of protein, saturated fat and dietary cholesterol than semi-vegetarians and non-vegetarians
  • Vegetarians had higher polyunsaturated-to-saturated fat ratio than semi-vegetarians and non-vegetarians
  • Vegetarians had higher fiber consumption relative to energy intake.

Nutrient Intake of the Three Groups of Black Adults

Nutrient Vegetarian Semi-Vegetarian Non-Vegetarian
Energy (kcal) 2,272±115 2,574±197 2,603±279

Carbohydrate (g)
Percentage of Energy

339±19.0
58.1±1.1

365±29.7
55.3±1.3

368.6±41.1
55.3±1.5

Protein (g)
Percentage of Energy

72.7±4.3
12.4±0.3a

94.7±8.2
14.5±0.5b

95.6±10.9
14.1±0.4b

Fat (g)
Percentage of Energy

75.8±4.5
29.5±1.0

88.0±7.5
30.3±1.1

91.4±10.3
30.2±1.3

Saturated Fatty Acids (g)
Percentage of Energy

16.3±1.2a
6.5±0.3a

21.5±1.9
7.7±0.4b

24.9±3.2b
8.3±0.4b

Polyunsaturated Fatty Acids (g)
Percentage of Energy

19.5±1.4
8.1±0.5

19.9±1.9
7.2±0.4

20.7±2.3
7.4±0.5

Cholesterol  (mg) 109.6±11.5a 218.7±22.5b 248±28.4b
Potassium (mg) 3,661±214 4,179±339 3,903±407
Calcium (mg) 720.2±52.5a 984.3±82.6b 878.5±91.4
Sodium (mg) 2,841±208 3,068±300 2,833±329
Polyunsaturated:Saturated Fatty Acids 1.3±2.5 0.9±0.05b 0.9±0.05b
Fiber (g) 36.0±2.5 35.5±3.2 33.8±3.6

±SEM not sharing a common superscript letter indicates significantly different from each other, P<0.05.

Blood Pressure by Dietary Habits of Black Adults

There were no significant group differences in either systolic or diastolic BP (adjusted for age and sex) and the same held true when those on anti-hypertensive medications were excluded.

  Vegetarian
N=66

Semi-Vegetarian
N=56

Non-Vegetarian
N=45
Systolic Blood Pressure (mmHg) 116.6±2.5 121.0±2.6 120.2±2.7
Diastolic Blood Pressure (mmHg) 77.2±1.4 77.5±1.3 78.5±1.6
Adjusted (for Age and Sex) Systolic BP 117.5±1.9 120.1±2.1 120.4±2.3
Adjusted (for Age and Sex) Diastolic BP 77.6±1.3 77.2±1.4 78.5±1.5

Serum Lipids and Serum Glucose by Dietary Habits

  • Vegetarians vs. non-vegetarians exhibited lower serum concentrations of serum total cholesterol, LDL cholesterol and triglycerides
  • There were no significant group differences in HDL cholesterol
  • CVD risk factor ratios (STC/HDL cholesterol and LDL cholesterol/HDL cholesterol)  were lower for vegetarians than non-vegetarians
  • The groups did not differ in fasting blood glucose concentrations.

Serum Lipids and Serum Glucose by Dietary Habits of Black Adults

  Vegetarian
N=66
Semi-Vegetarian
N=56
Non-Vegetarian
N=45
Serum Total Cholesterol (mmol/L) 4.7±0.1a 4.9±0.2a 5.4±0.2b
LDL-C; Low-Density Lipoprotein (mmol/L) 3.1±0.1a 3.3±0.1 3.6±0.2b
HDL-C; High-Density Lipoprotein (mmol/L) 1.2±0.1 1.2±0.1 1.3±0.1
STC/HDL-C 4.0±0.2a 4.4±0.2 4.7±0.3b
LDL-C/HDL-C 2.7±0.1a 2.9±0.2 3.2±0.3b
Triglycerides (mmol/L) 1.1±0.1a 1.3±0.1 1.5±0.1b
Glucose (mmol/L) 5.2±0.3 5.5±0.2 5.6±0.5

Means not sharing a common superscript letter are significantly different from each other, P<0.05.

Other Findings*

Simple correlation analysis with only variables related to the dependent variable showed:

  • Age was the variable most strongly correlated with both systolic and diastolic BP
  • Indicators of central body fat patterning (waist circumference, waist-to-hip ratio and waist-to-thigh ratio) were more strongly correlated with BP than peripheral fat patterning (hip circumference, thigh circumference and triceps skinfold)
  • Central fat patterning was also related to serum lipids
  • The polyunsaturated saturated fat ratio was positively related to HDL cholesterol and inversely related to BP, triglyceides and CVD risk ratios (STC/HDL cholesterol and LDL cholesterol/HDL cholesterol)
  • Protein intake correlated with both systolic BP (R=0.17, P<0.05) and diastolic BP (R=0.27, P<0.001)
  • Dietary cholesterol was correlated with systolic BP (R=0.18, P<0.05) and diastolic BP (R=0.15, P<0.05), but not with any blood lipids
  • Total fat intake was related to diastolic BP (R=0.15, P<0.05) as was saturated fat (R=0.20, P<0.01)
  • Polyunsaturated fat was inversely associated with both STC/HDL cholesterol (R=-0.15, P<0.05) and LDL cholesterol/HDLcholesterol (R= 0.18, P<0.05)
  • Dietary fiber intake was inversely associated with serum glucose (R=-0.16, P<0.05), but not with BP or any blood lipids.

Multiple regression analysis to determine best predictors of BP and blood lipids showed:

  • Age, waist thigh ratio and percentage of energy as protein together explained 35% of the variability in systopic BP
  • Age and absolute intake of protein together explained 13% of variability of diastolic BP
  • Age and central fat patterning were important predictors for serum lipids.
Author Conclusion:
  • Black Seventh-Day Adventist vegetarians exhibited lower waist-to-height ratios, less hypertension and lower concentrations of serum total cholesterol, low-density lipoproteins, triglycerides, serum total cholesterol, high-density lipoprotein ratio and low-density lipoprotein-to-high-density lipoprotein ratio, compared with non-vegetarians and semi-vegetarians
  • The lower values for these CVD risk indicators were related to less central body fat patterning, lower saturated fat intake and higer polyunsaturated-to-saturated fat ratio.
Funding Source:
University/Hospital: Colorado Agricultural Experimental Station
Reviewer Comments:
  • This study indicates that black adult vegetarians compared with non-vegetarians had lower average blood lipid risk factors for CVD and that these results were similar to those found in previous cross-sectional studies of white vegetarians and non-vegetarians
  • There were no differences in blood pressure between the vegetarians and non-vegetarians in these black adults, whereas in previous studies of white populations, there were blood pressure differences. However, in this study of black adults, there was a significantly higher percentage of subjects taking anti-hypertensive medications in the semi- and non-vegetarian groups
  • Also, the black vegetarians on hypertensive medications had considerably higher blood pressure than the group mean
  • When the vegetarian group without those on anti-hypertensive medications was compared to non-vegetarians, the blood pressure did show significant differences.
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) 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? 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) 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? 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? 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%.) 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? 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? 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? 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? 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? 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? 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? 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