EAL

DF: Cardiovascular Disease (2008)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

To examine the effects of low- and high-fiber meals on postprandial serum glucose, insulin, lipid, lipoprotein and apolipoprotein levels among men with high cholesterol.

Inclusion Criteria:

Male
With hypercholesterolemia (multiple serum cholesterol level higher than 5.2mmol per L)
Non-obese (specific definition was not reported)
Middle-aged (specific age requirement was not reported)
Without diabetes, renal disease, liver disease, thyroid disease, other secondary causes of hyperlipidemia
Not on lipid-lowering medications for three months or more before enrollment into the study.

Exclusion Criteria:

None except not meeting inclusion criteria.

Description of Study Protocol:

Design

Randomized crossover design, with two treatment periods of three days and a washout period of four days in between.

Intervention

Treatment periods lasted for three days. On day one, subjects ate a low-fat, low-fiber meal (35% of estimated kcal need, 65% kcal from CHO, 15% kcal from protein, 20% kcal from fat, 200mg cholesterol per 1,000kcal, 3g fiber per 1,000kcal) at 5:30 P.M. and then fast for 14 hours. On day two, subjects ate three treatment meals, at 7:30 A.M., 12:30 P.M. and 5:30 P.M., and then fasted for 14 hours. On day three, subjects ate a "large single meal" at 7:30 A.M. and then fasted. Treatment meals (ate on day two and three) were either high fiber or low fiber. Both high- and low-fiber meals had 40% kcal from CHO, 45% kcal from fat, 15% kcal from protein and had similar amounts of saturated fat, monounsaturated fat, polyunsaturated fats and cholesterol. High fiber meals had eight times the amount of fiber in low fiber meals. Fiber was from both food and psyllium.

Statistical Analysis

Two-factor (time and diet) repeated measures ANOVA, paired T-tests.

Data Collection Summary:

Timing of Measurements

Blood samples were collected hourly on day two from 8:30 A.M. to 10:30 P.M. and on day two from 8:30 A.M. to 4:30 P.M.

Dependent Variables

Serum glucose: Analyzed using glucose oxidase
Serum insulin: Analyzed by immunoassay
Serum free fatty acid: Enzymatic colorimetric method
Serum cholesterol: Measured using cholesterol esterase-cholesterol oxidase assay
Serum triglyceride (TG): By hydrolyzing the TG and measuring the released glycerol
Serum HDL: Measured using cholesterol esterase-cholesterol oxidase assay
Serum HDL2: Vertical autoprofile measurements
Serum HDL3: Vertical autoprofile measurements
Serum LDL: Vertical autoprofile measurements
Serum VLDL: Vertical autoprofile measurements
Serum ILDL: Vertical autoprofile measurements
Apolipoprotein A-I: Radioimmunodiffusion method
Apolipoprotein B-100: Radioimmunodiffusion method.

Independent Variables

Assigned treatment (high- or low-fiber meals).

Description of Actual Data Sample:

Initial N: 10
Attrition: 10 for most measures, six for VAP analysis for multiple meal day, seven for VAP analysis for single meal day
Age: Mean 62.7, SD 2.5, range 43 to 70
Anthropometrics: BMI mean 26.3, SD 2.0, range 21.4 to 28.3.

Summary of Results:

**Fasting Levels on Single-meal Day (Day Three)**
Fasting Levels	Low-fiber Meal (Mean ± SEM)	High-fiber Meal (Mean ± SEM)
Glucose (mmol per L) (N=10)	5.53±0.13	5.58±0.16
Insulin (pmol per L) (N=10)	72.9±11.1	46.5±1.4
Free fatty acid (mEq per L) (N=10)	0.81±0.21	0.66±0.1
Triglycerides (mmol per L) (N=10)	1.90±0.23	2.08±0.28
Cholesterol (mmol per L) (N=10)	5.81±0.19	5.67±0.19
HDL (mmol per L) (N=10)	1.05±0.08	1.03±0.07
LDL (mmol per L) (N=7)	3.05±0.11	2.86±0.16
VLDL (mmol per L) (N=7)	0.88±0.09	0.84±0.07
ILDL (mmol per L) (N=7)	1.06±0.05	0.94±0.04
HDL2 (mmol per L) (N=7)	0.147±0.021	0.147±0.021
HDL3 (mmol per L) (N=7)	0.705±0.065	0.700±0.072
Apo B-100 (g per L) (N=10)	1.09±0.07	1.06±0.05
Apo A-I (g per L) (N=10)	1.65±0.11	1.66±0.1

**Fasting Levels on Multiple Meal Day (Day Two)**
Fasting Levels	Low-fiber Meal (Mean ± SEM)	High-fiber Meal (Mean ± SEM)
Glucose (mmol per L) (N=10)	5.30±0.08	5.52±0.17
Insulin (pmol per L) (N=10)	60.4±6.9	56.9±6.3
Free fatty acid (mEq per L) (N=10)	0.63±0.11	0.91±0.29
Triglycerides (mmol per L) (N=10)	1.92±0.28	2.13±0.26
Cholesterol (mmol per L) (N=10)	5.65±0.18	5.74±0.23
HDL (mmol per L) (N=10)	1.05±0.09	1.01±0.07
LDL (mmol per L) (N=6)	2.92±0.09	2.78±0.22
VLDL (mmol per L) (N=6)	0.78±0.05	0.72±0.07
ILDL (mmol per L) (N=6)	1.02±0.13	0.86±0.10
HDL2 (mmol per L) (N=6)	0.189±0.054	0.168±0.047
HDL3 (mmol per L) (N=6)	0.796±0.101	0.767±0.085
Apo B-100 (g per L) (N=10)	1.03±0.06	0.99±0.05
Apo A-I (g per L) (N=10)	1.63±0.1	1.68±0.09

Findings

For single meal day (day three): Serum glucose was lower with HF than with LF meals (P=0.019). Peak glucose levels were 7.6±1.4mmol per L with HF meals and 9.6±1.5 with LF meals (P<0.001). Incremental peaks, i.e., mean of individual increases above fasting levels were 2.0±1.2mmol per L with HF meals and 4.2±1.3 with LF meals (P<0.001).
For multiple meal day (day two): Serum glucose were lower with HF than with LF meals (P=0.0043). Peak glucose levels were 7.8±1.4mmol per L with HF meals and 9.6±1.5 with LF meals (P<0.001). Incremental peaks, i.e., mean of individual increases above fasting levels were 2.3±1.2mmol per L with HF meals and 4.3±1.4 with LF meals (P<0.001).
On both single meal and multiple meals days, serum insulin changed significantly over time (P<0.0005), and were lower with HF meal than with LF meal at one hour after single meal on day three and at one hour after lunch on day two
TG, cholesterol and HDL generally did not differ between HF and LF except certain time points. These differences do not exhibit any patterns.
HDL: No difference between HF and LF
Apo B-100: Lower in LF than in HF
apo A-I: No significant difference between HF and LF.

Author Conclusion:

Dietary fiber affects postprandial blood glucose and insulin responses, but very little effects on postprandial serum lipids, lipoproteins and apolipoproteins.

Funding Source:

Industry:

Procter & Gamble

Other:

Not-for-profit

Reviewer Comments:

It is unclear how subjects were recruited, and inclusion criteria were vague. For example, weight and age requirements were not specifically defined.
It is unclear what the exact research question was. According to the results, authors were looking for differences in all of the outcome variables at every single possible time points on day two and three. It is unsure how these seemingly random observations can be interpreted meaningfully. This also risks the danger of multiple comparisons, which the authors did not adjust for in their analysis.
Also, the authors did not report or measure weight change during the study, which could potentially be a confounder in this metabolic study
Sample size was small. Besides, not all 10 subjects provided complete data.

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?		No
	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?	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?	???
	2.2.	Were criteria applied equally to all study groups?	No
	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?	???
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?		???
	4.1.	Were follow-up methods described and the same for all groups?	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%.)	N/A
	4.3.	Were all enrolled subjects/patients (in the original sample) accounted for?	No
	4.4.	Were reasons for withdrawals similar across groups?	No
	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?	No
	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.)	No
	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?		Yes
	6.1.	In RCT or other intervention trial, were protocols described for all regimens studied?	Yes
	6.2.	In observational study, were interventions, study settings, and clinicians/provider described?	N/A
	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?	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?	N/A
	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?	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?		No
	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)?	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?	No
9.	Are conclusions supported by results with biases and limitations taken into consideration?		No
	9.1.	Is there a discussion of findings?	Yes
	9.2.	Are biases and study limitations identified and discussed?	No
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