EAL

DLM: Fiber (2007)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

To examine the association between dietary fiber intake and peripheral arterial disease (PAD) risk in men.

Inclusion Criteria:

Subjects from the Health Professionals Follow Up Study; males ages 40-75 who volunteered

*answered questionnaires at baseline and every 2 years for 12 years

*FFQ at baseline and every 4 years for 12 years

Exclusion Criteria:

*Hx peripheral arterial disease (PAD), CHD, DM, stroke

*the following inadequate dietary data at enrollment:

*intake <3352 kj or >17598 kj or

*>70 unanswered questions of 131 on FFQ

Description of Study Protocol:

A 12 year study.

Subjects were volunteer participants in the Health Professionals Study of 1986.

Subjects answered questionnaires at baseline and every 2 years thereafter ascertaining medical condition and lifestyle.

Answered a validated FFQ every 4 years

Nutrient content of foods was estimated using 1. The Harvard University Food Composition Database (derived from USDA sources) 2. Manufacturers info. 3. Data from peer reviewed literature.

The baseline and f/u questionnaires obtained data on age, smoking, HTN, hypercholesterolemia, angina, supplement use, wt, and physical activity.

From these BMI and energy expenditure were calculated.

When an incidence of peripheral arterial disease (PAD) was identified it was associated with the diet intake encompassing the previous questionnaire period.

FFQ were no longer included in the study for subjects who developed heart disease, stroke or had a CABG due to the assumption that their diets would change as a result. Data from the preceding questionnaire replaced data for the current one.

Peripheral arterial disease (PAD) cases were considered “definite” if subjects who reported intermittent claudication or surgery for PAD had their dx confirmed via 1. surgical report in medical record 2. Ankle Brachial blood pressure index (ABPI) <0.80 3. MD dx 4. angiogram or Doppler ultrasound showing 50% or more obstruction of at least one artery plus symptoms in the ipsilateral limb.

PAD cases were deemed “probable” if a subject confirmed a PAD by letter or telephone without a medical record to back it up.

Incident cases = definite + probable

Data Collection Summary:

No blinding used.

Medical and lifestyle obtained upon enrolment (baseline) and every 2 years thereafter fir 12 years.

These questionnaires obtained info on age, smoking, diagnosed or treated HTN, hypercholesterolemia, angina, supplement use, wt and physical activity. Average amount of time spent per week walking, jogging, running bicycling, calisthenics, aerobics, machine rowing, swimming, squash, tennis, racquetball.

BMI and energy expenditure data derived from these responses.

FFQ obtained at baseline and every 4 years thereafter for 12 years.

Description of Actual Data Sample:

46,032 professional men

ages 40-75 at baseline.

The drop out rate was not specifically reported.

Summary of Results:

308 incident cases of PAD at end of study.

223 cases were definite:

113 had peripheral arterial disease (PAD) surgery
58 had ABPI <0.8
47 had MD diagnosis
7 had Doppler ultrasound results

85 were probable:

73 by letter
12 by phone

	Quintile 1	Quintile 5
Total Fiber	13.4 g/d	29.6 g/d
Cereal Fiber	2.5 g/d	10.2 g/d

Men in quintile 5 of total fiber were less likely to smoke, drink alcohol, were slightly leaner and exercised more.

Cereal fiber intake was inversely assoc with peripheral arterial disease (PAD) risk when adjusted for age.

Men in quintile 5 of cereal fiber had 33% lower rate of PAD than men in the bottom quintile (RR=0.67, 95%CI, 0.47-0.97, P=0.07).

The association between cereal fiber and risk was nonlinear in the multivariate cubic spline model (P=0.02) and significant (P=0.03),

The maximum risk reduction was achieved with 5 g/d of cereal fiber intake. More intake did not further reduce risk.

Whole grain intake was inversely assoc with PAD risk (RR=0.67, 95% CI, 0.47-1.06 P=0.05) when comparing top and bottom quintiles.

Insoluble fiber was also inversely assoc with PAD risk (RR=0.53, 95% CI, 0.35-0.79P=0.02) when comparing top and bottom quintiles.

Soluble fiber was not assoc with risk reduction when comparing top and bottom quintiles (RR=0.77, 95% CI 0.53-1.12, P=0.09).

The interaction between cereal fiber intake and PAD was not significant among subgroups as follows:

age (<65 and >/=65, P=0.23)
smoking (never smokers and ever smokers, P=0.46)
BMI (<25 and >/=25, P=0.89)

The association between cereal fiber and PAD risk was stronger for men who took vitamin E supplements (P=0.02).®see reviewer’s comments®

Fruit, veg, and total fiber were not assoc with PAD risk.

Author Conclusion:

The inverse association between cereal fiber and PAD risk is probably not entirely due to serum chol reduction but also improved insulin sensitivity, reduced glucose levels, production of short-chain fatty acids by gut bacteria thereby further improving glucose metabolism.

Vitamin E has previously been shown to prevent LDL oxidation and increase lipoprotein lipase activity therefore it likely enhanced the cereal fibers ability to reduce PAD risk seen in this study.

Increased dietary cereal fiber intake in male smokers and nonsmokers is assoc w/reduced risk of PAD therefore increasing cereal fiber could contribute to prevention of PAD.

Funding Source:

Government:

NIH

Not-for-profit

Foundation associated with industry:

Reviewer Comments:

The results section was confusing when one tried to verify/understand the statistics. One example is the mention of soluble and insoluble fiber yet these are not found on any tables. The study mentions looking at soluble and insoluble fiber in the statistical analysis section but does not describe anything about it or the foods it was found in. Also there is mention of “whole grain intake” being found in the cereal fiber as if they are changing terminology from looking at cereal fiber to suddenly talking about whole grain fiber.

The authors did not describe all of the sources of fiber on the table yet mention other sources in the text. For example the cereal, fruit and veg fiber does not add up to total fiber. During the discussion they mention rye bread as being the main source of “dietary fiber” yet “dietary fiber” was not a term previously used and we don’t know how much rye bread the subjects ate.

The authors talk about ascertaining the subjects deaths by >98% but we don’t know the number of subjects who died or any drop-out info.

The association between cereal fiber and PAD risk was stronger for men who took vitamin E supplements (P=0.02).®The table in the paper that this is reported on says “0.07” not 0.02.

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
	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?	N/A
	1.2.	Was (were) the outcome(s) [dependent variable(s)] clearly indicated?	N/A
	1.3.	Were the target population and setting specified?	N/A
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?	N/A
	2.2.	Were criteria applied equally to all study groups?	N/A
	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?	N/A
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?		No
	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
	4.3.	Were all enrolled subjects/patients (in the original sample) accounted for?	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
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
	5.2.	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.)	N/A
	5.3.	In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded?	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
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
	6.2.	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?	No
	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?		Yes
	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?	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?	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?	N/A
	7.7.	Were the measurements conducted consistently across groups?	N/A
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?	N/A
	8.2.	Were correct statistical tests used and assumptions of test not violated?	N/A
	8.3.	Were statistics reported with levels of significance and/or confidence intervals?	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)?	N/A
	8.6.	Was clinical significance as well as statistical significance reported?	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
	9.1.	Is there a discussion of findings?	N/A
	9.2.	Are biases and study limitations identified and discussed?	N/A
10.	Is bias due to study's funding or sponsorship unlikely?		Yes
	10.1.	Were sources of funding and investigators' affiliations described?	N/A
	10.2.	Was the study free from apparent conflict of interest?	N/A