EAL

AWM: Low Glycemic Diets (2006)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

To evaluate the effects of consuming high- and low-glycemic index/glycemic load meals, matched on macronutrient composition and palatability, plasma glucose, and insulin, appetite, and food intake.

Inclusion Criteria:

Healthy nonsmoking adults, not using medication (except birth control pills), not pregnant or lactating, not on a therapeutic diet, had no recent weight loss or gain > 3 kg over previous 3 months, had regular eating habits (daily breakfast, lunch, dinner consumption), fasting blood glucose 70 - 110 mg/dl, no family history of diabetes, no celiac disease, and had dietary restraint < 14.

Exclusion Criteria:

Excluded if not included above.

Description of Study Protocol:

Recruitment

Recruited through public advertisements.

Design

Randomized Controlled Clinical Trial. Randomized by coin flip to high- or low-glycemic index groups.

Blinding used (if applicable)

Not used.

Intervention (if applicable)

Subjects consumed only low- or high-glycemic index foods ad libitum in the laboratory for 8 days in either high (3 foods per meal) or low (1 food per meal) conditions.

Statistical Analysis

Glycemic response, insulin response, appetite, and intake analyses were conducted by repeated-measures ANOVA. Day, meal, and time were within-subjects factors, while glycemic index group was a between-subjects factor. Pearson bivariate correlation coefficients were calculated to evaluate the relationship between glycemic response (area under the curve), insulin response (area under the curve), and appetitive ratings (area under the curve) on days 1 and 8 of each study session.

Data Collection Summary:

Timing of Measurements

Two experimental 8-day sessions separated by washout period of 15 days. Energy intake was monitored daily. Glucose, insulin and appetitive sensations determined before and at 30, 60 and 120 minutes following breakfast and lunch on days 1 and 8.

Dependent Variables

Blood glucose assessed with SureStep LifeScan
Serum insulin determined by solid-phase 2-site enzyme immunoassay
Appetite assessed by ratings of hunger, desire to eat, and fullness at stipulated times. Food pleasantness rated after initial tasting. All ratings made on general labeled magnitude scales
Body fat measured through bioelectrical impedance analysis

Independent Variables

Low glycemic index (1 food per meal) or high glycemic index (3 foods per meal) consumed ad lib in the laboratory for 8 days. 79 foods were selected based on similar macronutrient composition and published glycemic index values. Ratings for foods confirmed through pretest with 13 nonstudy adults. 48 foods resulted in consistent responses were selected as test foods. Participants returned unconsumed snacks daily. Consumption of nonstudy foods or beverages were prohibited. Blood glucose taken before each meal to ensure subjects had not eaten. Food intake was measured. Asked to maintain constant level of activity. RD analyzed the dietary intake data.

Control Variables

Description of Actual Data Sample:

Initial N: 39 healthy adults, 19 female, 20 male

Attrition (final N): See above

Age: 24.9 +/- 0.8 years

Ethnicity: Not mentioned

Other relevant demographics: Mean BMI: 22.9 +/- 0.5, mean body fat 23.5 +/- 1.0%

Anthropometrics: There were no statistically significant group baseline characteristic differences.

Location: Purdue University, Indiana

Summary of Results:

Other Findings

Low and high-glycemic index foods had mean glycemic index values of 43.81 +/- 0.99 (range 30.09 - 49.62) and 105.26 +/- 5.74 (68.70 - 169.30), respectively.

Group glycemic responses and insulinemic responses did not significantly differ following breakfast or lunch on day 1 or 8 of either session.

There were no significant group differences in hunger, fullness, or desire to eat ratings. No significant correlation between any appetite index rating and glycemic or insulinemic responses were observed.

There was no group difference in energy or macronutrient intake.

Author Conclusion:

In summary, the present findings reveal that ad libitum ingestion of only empirically documented low- or high-glycemic index foods, served individually and in mixed meals and matched individually for macronutrient composition and palatability, does not elicit a differential glycemic or insulinemic response either acutely or over a multiday period. Further, there were no significant differences of appetite or energy or macronutrient intake on any assessment day or overall. Although there may be important associations between dietary glycemic index and disease risk, the present findings raise questions about the predictive power of the glycemic index of a specific food or diet for either appetitive or dietary responses.

Funding Source:

Reviewer Comments:

Food consumed in lab.

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?	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?	Yes
	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)	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
	3.4.	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?		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?	Yes
	6.5.	Were co-interventions (e.g., ancillary treatments, other therapies) described?	Yes
	6.6.	Were extra or unplanned treatments described?	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
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?	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
	7.7.	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