DLM: Fiber (2007)
Examine the relationship of dietary fiber intake to subsequent risk of CVD in a nationally representative sample of the US no institutionalized population.
Participants in NHANES I between the ages of 25-74 years.
During initial NHANES I survey:
•No dietary information was available.
•There was missing gram amounts of food eaten.
•Self-reported history of myocardial infarction, heart failure, or stroke at baseline.
•Taking medication for heart disease.
•Participation in follow-up analysis
NHANES I baseline date collection(1971-1975):
•Medical history and dietary assessment questionnaires
•Laboratory test
•Anthropometric measurements.
Dietary assessment included single 24-hour dietary recall at baseline.
Follow-up data was collected between 1982 and 1984, and in 1986, 1987, and 1992 for incidence and mortality from coronary heart disease (CHD) and cardiovascular disease CVD.
NHANES I baseline date collection (1971-1975):
•Medical history and dietary assessment questionnaires
•Laboratory test
•Anthropometric measurements.
Dietary assessment included single 24-hour dietary recall at baseline. Dietary analysis of NHANES I 24-hour dietary recall using ESHA food processor nutrient databases.
Follow-up data was collected between 1982 and 1984, and in 1986, 1987, and 1992 for incidence and mortality from coronary heart disease (CHD) and cardiovascular disease CVD.
Total fiber-calorie and soluble fiber-calorie ratios were expressed as grams per 1735 kcal, the average calorie intake of the study population.
Four groups were identified in quintiles of Total Dietary Fiber-Calorie Ratio, g/1735 kcal:
1) Lowest <7.7 2) 7.7-11.0 3) 11.1-15.9 4) Highest >15.9
Four groups were identified in quintiles of Soluble Dietary Fiber-Calorie Ratio, g/1735 kcal:
1) Lowest <1.3 2) 1.3-2.3 3) 2.4-4.0 4) Highest >4.0
Primary end points were incidence and mortality from coronary heart disease and cardiovascular disease.
Total of 9776 persons
•14407 persons in age range of 25-74 years.
•3059 excluded d/t no dietary information.
•45 excluded d/t missing gram amounts of food.
•1132 excluded d/t self-reported history of myocardial infarction, heart failure, or stroke at baseline or had used medication for heart disease in the last 6 months.
•395 were lost to follow-up.
•Median total dietary fiber (TDF) intake per 1735 kcal was 11.2g/d.
•Median soluble dietary fiber (SDF) intake per 1735 kcal was 2.4 g/d.
•Median TDF intake in highest quartile was 20.7g/d.
•Median TDF intake in lowest quartile was 5.9g/d.
•Median SDF intake in highest quartile was 5.9g/d.
•Median SDF intake in lowest quartile was 0.9g/d.
At baseline: after adjusting for age, higher intake of TDF was found to be associated with:
1) Lower systolic and diastolic blood pressure. Although, there was not a significant difference in proportions of hypertension.
2) More likely to have Diabetes mellitus.
3) Less likely to be smokers.
4) Less likely to drink alcohol regularly.
5) Consumed less saturated fat .
6) Consumed fewer calories
*Trends were similar when participants were divided according to their intake of soluble fiber, with the exceptions of education level and physical activity (More soluble fiber intake was associated with lower education level and less physical activity).
Follow-up between 1971 and 1992:
1) 928 stroke events (223 fatal)
2) 1843 CHD events (668 fatal)
3) 3762 CVD events (1198 fatal)
4) 2632 deaths from all causes
After TDF was adjusted for age, race, and sex, no statistical significance was observed between quintiles for CHD, CVD, stroke, incidence, and mortality (p>0.05).
After TDF was adjusted for multivariate risk factors, mortality from CHD and CVD no statistical significance was observed between quintiles (p>0.05).
TDF intake in all quintiles (excluding the lowest quintile with a RR of 1 and <7.7gm/1735kcal) resulted in a reduced CHD incidence after adjustment for multivariate risk factors.
2nd quintile 1.01
3rd quintile 0.91
4th quintile 0.88
TDF intake in all quintiles (excluding the lowest quintile with a RR of 1 and <7.7gm/1735kcal) resulted in a reduced CVD incidence after adjustment for multivariate risk factors.
2nd quintile 1.02
3rd quintile 0.93
4th quintile 0.89
SDF intake in all quintiles (excluding the lowest quintile with a RR of 1 and <1.3gm/1735kcal) resulted in a reduced CHD incidence after adjustment for Age, race, and sex; multivariate risk factors.
Age, race, sex Multivariate risk factors
2nd quintile 1.00 2nd quintile 1.04
3rd quintile 0.86 3rd quintile 0.88
4th quintile 0.89 4th quintile 0.85
SDF intake in all quintiles (excluding the lowest quintile with a RR of 1 and <1.3gm/1735kcal) resulted in a reduced CVD incidence after adjustment for Age, race, and sex; multivariate risk factors.
Age, race, sex Multivariate risk factors
2nd quintile 0.99 2nd quintile 1.02
3rd quintile 0.91 3rd quintile 0.94
4th quintile 0.93 4th quintile 0.90
SDF intake in all quintiles (excluding the lowest quintile with a RR of 1 and <1.3gm/1735kcal) resulted in a reduced CHD and CVD mortality after adjustment for multivariate risk factors.
CHD CVD
2nd quintile 0.95 2nd quintile 0.91
3rd quintile 0.80 3rd quintile 0.76
4th quintile 0..76 4th quintile 0..88
A 10g/d increase in TDF was associated with a 7% lower incidence of CHD and CVD.
A 5g/d increase in absolute intake of soluble fiber was associated with a 6% lower incidence of CHD and a 5% lower incidence of CVD.
The study findings can be generalized on a national level because the NHANES I Epidemiologic Follow-up study cohort is a random sample of the adult noninstitutionalized population.
One limitation of the study is that dietary fiber was estimated using a single 24-hour dietary recall. This may result in misclassification of usual dietary fiber intake at the individual level.
In addition, dietary fiber intake was not collected during the follow-up.
The study finds suggest that a diet high in dietary fiber, particularly of water-soluble fiber, is strongly and independently associated with a lower risk of CHD and CVD and mortality.
| Government: | NIH | ||
| Industry: |
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The main concerns I had about this paper were addressed as limitations in the study discussion. Otherwise, I felt this was a through analysis of available data.
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Quality Criteria Checklist: Primary Research
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| 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 | |
| 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 | |
| 4. | Is the intervention or procedure feasible? (NA for some epidemiological studies) | Yes | |
| Validity Questions | |||
| 1. | Was the research question clearly stated? | Yes | |
| 1.1. | Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? | Yes | |
| 1.2. | Was (were) the outcome(s) [dependent variable(s)] clearly indicated? | Yes | |
| 1.3. | Were the target population and setting specified? | 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 | |
| 2.2. | Were criteria applied equally to all study groups? | Yes | |
| 2.3. | Were health, demographics, and other characteristics of subjects described? | N/A | |
| 2.4. | Were the subjects/patients a representative sample of the relevant population? | 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 | |
| 3.2. | 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 | |
| 3.4. | 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? | N/A | |
| 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.) | 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 | |
| 4.1. | 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%.) | Yes | |
| 4.3. | Were all enrolled subjects/patients (in the original sample) accounted for? | Yes | |
| 4.4. | Were reasons for withdrawals similar across groups? | Yes | |
| 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 | |
| 5.1. | In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? | 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.) | ??? | |
| 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 | |
| 5.5. | 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 | |
| 6.1. | 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? | No | |
| 6.3. | Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? | Yes | |
| 6.4. | Was the amount of exposure and, if relevant, subject/patient compliance measured? | N/A | |
| 6.5. | Were co-interventions (e.g., ancillary treatments, other therapies) 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 | |
| 6.8. | 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 | |
| 7.1. | 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 | |
| 7.3. | Was the period of follow-up long enough for important outcome(s) to occur? | Yes | |
| 7.4. | Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? | No | |
| 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 | |
| 7.7. | Were the measurements conducted consistently across groups? | Yes | |
| 8. | Was the statistical analysis appropriate for the study design and type of outcome indicators? | Yes | |
| 8.1. | 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 | |
| 8.3. | 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 | |
| 8.5. | 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 | |
| 8.7. | 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 | |
| 9.1. | Is there a discussion of findings? | Yes | |
| 9.2. | Are biases and study limitations identified and discussed? | Yes | |
| 10. | Is bias due to study's funding or sponsorship unlikely? | Yes | |
| 10.1. | Were sources of funding and investigators' affiliations described? | Yes | |
| 10.2. | Was the study free from apparent conflict of interest? | Yes | |