Vegetarian Nutrition

VN: Cardiovascular Disease (2008)

Citation:

Williams PT. Interactive effects of exercise, alcohol and vegetarian diet on coronary artery disease risk factors in 9242 runners: The National Runners' Health Study. Am J Clin Nutr. 1997 Nov; 66 (5): 1,197-1,206.

PubMed ID: 9356539
 
Study Design:
Cross-sectional study
Class:
D - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:

The purpose of this research was to examine associations among diet, distance run and coronary artery disease risk factors in vegetarian and omnivorous runners.

Inclusion Criteria:
  • No previous history of heart disease or cancer
  • No medications that might affect lipoprotein concentrations.
Exclusion Criteria:
  • Previous history of heart disease or cancer
  • Medications that might affect lipoprotein concentrations.
Description of Study Protocol:
  • Recruitment: Participants were recruited at national running races and through advertisements in Runner's World magazine.
  • Design: Cross-sectional study.
  • Statistical analysis: Multiple-regression analyses were used to test for linear relations between distance run and risk factor status. Logistic regression was used to examine trends for nominal data.
Data Collection Summary:

Timing of Measurements

Runners completed a two-page self-admininstered questionnaire. The questionnaire included a request to obtain the runner's height, weight, blood lipid profile, blood pressure and resting heart rate from their physicians.

Variables

  • Assessed using a two-page self-administered questionnaire:
    • Demographics
    • Running history
    • Weight history
    • Diet (self-identified vegetarianism and current weekly intakes of alcohol, red meat, fish and fruit)
    • Cigarette use
    • Medical and medication history
    • Anthropometrics (height, weight, waist circumference, hip circumference, chest circumference).
  • Assessed via physician-supplied information:
    • Height
    • Weight
    • Blood lipid profile
    • Blood pressure
    • Resting heart rate.
Description of Actual Data Sample:

Initial N

It was estimated that 15% to 19% of potential participants who recieved the questionnaire responded. Of those who responded, physician-obtained HDL-cholesterol was obtained from 26% of the respondents, including:

  • 820 male and 357 female vegetarian runners
  • 7,054 male and 1,837 female omnivorous runners.

Final N

After excluding self-proclaimed vegetarians who reported occasional weekly red meat or occasional fish intake, the sample in these analyses included:

  • 199 male and 152 female vegetarian runners
  • 7,054 male and 1,837 female omnivorous runners.

Age

  • Male vegetarians (45.18±9.36)
  • Male onmivores (38.05±9.64)
  • Female vegtarians (38.83±9.13)
  • Female onmivores (40.42±9.53).

Ethnicity

All white.

Summary of Results:

Characteristics

  • Among all runners, no significant differences between vegetarians and omnivores in the number of years run, resting pulse rate, blood pressure or ratio of total cholesterol to HDL-cholesterol
  • When compared to omnivorous runners, male and female vegetarians ran significantly further, consumed less alcohol, consumed more fruit, had lower BMIs and had smaller hips
  • When compared to omnivorous runners, male vegetarians had smaller waists and chests; lower total cholesterol, HDL-cholesterol and LDL-cholesterol; higher triacylglyerol concentration.

Comparisons Between Vegetarians and Omnivores

  • Male vegetarians were significantly lower on all blood lipid measures, except triglyceride levels (in which case, mean omnivore levels were lower). In contrast, there were no significant differences between female vegetarians and omnivores.
  • There was no significant difference in blood pressure measures for either male or female vegetarians and omnivores
  • For males, all measures of body composition were significantly lower in vegetarians than omnivores. For females, only BMI and hip circumference were significantly lower in vegetarians than omniovres.

Male Runners

Variables Male Vegetarians (N=199)
Mean±SD
Male Omnivores (N=7,054)
Mean±SD
Significance of Difference
Blood Lipids

Total Cholesterol (mmol/L)

4.91±1.0

5.08±0.89

P<0.01

HDL (mmol/L)

1.26±0.32

1.34±0.35

P<0.01

LDL (mmol/L)

3.08±0.91

3.22±0.81

P<0.05

Total:HDL (mmol/L)

4.13±1.32

4.03±1.23

NS

Triacylglcerol (mmol/L)

1.26±0.71

1.16±0.72

P<0.05

Blood Pressure

Systolic BP (mmHg)

122.09±15.04

121.66±13.37

NS

Diastolic BP (mmHg)

76.58±10.54

77.06±8.74

NS

Weight

Body Mass Index

22.91±2.43

23.78±2.47

P<0.0001

Waist (cm)

83.22±6.41

84.95±6.03

P<0.0001

Hip (cm)

92.85±6.53

95.23±7.09

P<0.001

Chest (cm)

100.37±7.24

101.58±6.95

P<0.05

Female Runners

  • Blood lipids: No significant difference on any blood lipids
  • Blood pressure: No significant difference in systolic or diastolic.

Variables

Female Vegetarians (N=152)
Mean±SD

Female Omnivores (N=1,837)
Mean±SD

Significance of Difference

Weight Measures

Body Mass Index

20.8±2.03

21.28±2.46

P<0.05

Waist (cm)

67.89±6.05

68.56±6.97

NS

Hip (cm)

90.72±5.83

91.82±6.5

P<0.05

Chest (cm)

87.98±4.48

87.95±5.38

NS

Associations with the Reported Distance Run Per Week

Among both male and female vegetarians, greater distance run was associated with greater concentrations of HDL-cholesterol and lower waist, hip and chest circumferences. Greater distance run was also associated with lower ratios of total-to-HDL-cholesterol in male vegetarians and lower BMI in female vegetarians.

When comparing vegetarians to omnivorous runners, the regression slopes reveal:

  • No significant difference relating weekly distance run to HDL-cholesterol, LDL-cholesterol, total cholesterol-to-HDL-cholesterol, triacylglycerols, systolic blood pressure and circumferences of the waist, hip and chest 
  • Per kilometer run per week, the associated reduction in BMI was 0.021±0.007 smaller in male vegetarians, compared to male omnivores (P=0.002; no difference in females)
  • Per kilometer run per week, the associated reduction in diastolic blood pressure was 0.08±0.04 greater in female vegetarians, compared to female omnivores (P=0.05; no difference in males).

Vegans (32 Males and 30 Females)

In a sub-analysis of vegans, greater weekly running distance was associated with the following (reported as slope±SE):

  • Greater HDL-cholesterol concentrations [by 0.006±0.002 (mmol per L) per km; P=0.002]
  • Lower systolic blood pressure [by 0.18±0.08 (mmol per L) per km; P=0.02]
  • Lower waist circumference (by 0.11±0.083cm per km; P=0.001)
  • The regression slopes for the remaining variables were not significant.

Alcohol

In the following multiple-regression analyses, omnivores and vegetarians were combined because results were nearly identical when analyzed separately. These analyses include a stratification of runners into five categories of alcohol intake (ml per week: Zero, one to 59, 60 to 118, 119 to 177 and more than 178) and four categories of running distance (km per week: Zero to 24, 24 to 48, 48 to 72 and more than 72).

For Men and Women

  • For nearly every level of alcohol intake, each 24-km increment in weekly running distance was associated with significantly higher HDL concentrations
  • Regression slopes between running distance and HDL-cholesterol were strongly significant regardless of alcohol consumption
  • Alcohol intake was associated with higher HDL-cholesterol regardless of running level.

For All Men

  • HDL-cholesterol increased (slope±SE) 0.0008±0.0001mmol per L per ml of alcohol consumed per week
  • HDL-cholesterol increased 0.0034±0.0002mmol per L per km run
  • There was no interaction between the effects of alcohol and weekly running distance on HDL (P=0.43 for interaction).

For All Women

  • HDL-cholesterol increased (slope±SE) 0.0009±0.0001mmol per L per ml of alcohol consumed per week
  • HDL-cholesterol increased 0.0034±0.0005mmol per L per km run
  • There was no interaction between the effects of alcohol and weekly running distance on HDL (P=0.68 for interaction).

Additional Alcohol Analyses Reveal

  • The percentage of men with high HDL was significantly greater with greater alcohol intake within all running distance strata (P<0.001) and significantly greater with greater running distance within all alcohol strata (P<0.001)
  • The percentage of women runners with high HDL-cholesterol increased linearly with increases in alcohol intake regardless of running distance and increased linearly with weekly running distance in three of the four alcohol-consumption groups (significance level not reported) 
  • In men, systolic and diastolic blood pressures were significantly greater with alcohol intake in all categories of running distance
  • In women, blood pressures were only weakly associated with alcohol intake.

Red Meat and Fruit Consumption

  • For men and women, diets containing high amounts of red meat were associated with higher BMIs and broader waistlines, generally significant within all running categories
  • For men (but not in women), diets containing higher amounts of fruit were associated with lower BMIs and slimmer waistlines
  • In men, the associations of BMI with fruit and meat diminishes with greater weekly running.
Author Conclusion:
  • Vigorous exercise provides important health benefits beyond those obtained by eating a vegetarian diet or consuming moderate amounts of alcohol alone
  • When compared to male omnivores, male vegetarian runners had lower BMIs; narrower waists, hips and chests; lower plasma concentrations of total-, HDL- and LDL-cholesterol; higher triacylglycerol concentrations
  • When compared to female omnivores, female vegetarians were leaner
  • Vegetarians and vegans who ran the farthest had higher HDL and lower waist circumferences
  • Running distance and alcohol intake contribute independently and additively to the production of high HDLs in runners
  • Runners who reported high intakes of red meat and low intakes of fruit tended to have a higher BMI
  • Limitations include:
    • Potential response bias
    • The use of conventional clinical measurements may be less precise than measurements made under usual research conditions
    • The assessment of diet was limited by only examining weekly intakes of red meat, fish and fruit.
Funding Source:
Government: NHLBI
Reviewer Comments:
  • The representativeness of the sample is a concern: HDL-cholesterol was only obtained from 26% of respondents and the entire sample was white. Furthermore, it is of interest to note that 621 of 820 (75%) self-proclaimed male vegetarians and 205 of 357 (42%) of self-proclaimed female vegetarians were completely excluded in the analyses because they subsequently reported occasional weekly red meat or occasional fish intake. It is unclear if the complete exclusion of these survey responders (i.e., as opposed to including then in the omnivores group) introduces bias. Furthermore, the validity of the fish consumption question is problematic: It was weakly correlated (R=0.19) to a four-day food record, presumably related to the infrequent intake of fish. Nevertheless, this question was used to exlude self-proclaimed vegetarians.
  • Due to the high misclassification of self-reported vegetarianism, the sub-analysis performed on vegans is concerning. There were no questions to confirm vegans (no dietary questions on dairy and eggs). 
  • It is unclear if the height and weight values used in the analyses were self-reported or provided by the physicians. It is assumed they are self-reported.
Quality Criteria Checklist: Primary Research
Relevance Questions
  1. Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies) Yes
  1. Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies) Yes
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? Yes
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? Yes
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice? Yes
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice? Yes
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) Yes
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) Yes
 
Validity Questions
  1. Was the research question clearly stated? Yes
1. Was the research question clearly stated? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? Yes
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? Yes
  1.3. Were the target population and setting specified? Yes
  2. Was the selection of study subjects/patients free from bias? 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? 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? N/A
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? N/A
  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%.) 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? ???
5. Was blinding used to prevent introduction of bias? ???
  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? ???
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? ???
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? N/A
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? N/A
  5.5. In diagnostic study, were test results blinded to patient history and other test results? N/A
  5.5. In diagnostic study, were test results blinded to patient history and other test results? N/A
  6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? Yes
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? Yes
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? N/A
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? N/A
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? Yes
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? Yes
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? 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? Yes
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? Yes
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? N/A
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? N/A
  6.6. Were extra or unplanned treatments described? N/A
  6.6. Were extra or unplanned treatments described? N/A
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? N/A
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? N/A
  6.8. In diagnostic study, were details of test administration and replication sufficient? N/A
  6.8. In diagnostic study, were details of test administration and replication sufficient? N/A
  7. Were outcomes clearly defined and the measurements valid and reliable? ???
7. Were outcomes clearly defined and the measurements valid and reliable? ???
  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? ???
  7.2. Were nutrition measures appropriate to question and outcomes of concern? ???
  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? ???
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? ???
  7.5. Was the measurement of effect at an appropriate level of precision? ???
  7.5. Was the measurement of effect at an appropriate level of precision? ???
  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? 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