EAL

PDM: Prediabetes (2013)

Citation:

Wolever TM, Mehling C. Long-term effect of varying the source or amount of dietary carbohydrate on postprandial plasma glucose, insulin, triacylglycerol and free fatty acid concentrations in subjects with impaired glucose tolerance. Am J Clin Nutr. 2003; 77: 612-621.

PubMed ID: 12600851

Study Design:

Randomized Controlled Trial

Class:

A - Click here for explanation of classification scheme.

Quality Rating:

NEUTRAL: See Quality Criteria Checklist below.

Research Purpose:

To determine whether reducing carbohydrate intake or reducing the glycemic index (GI) of the diet have the same long-term effects on post-prandial plasma glucose, insulin, triacylglycerol and free fatty acid (FFA) concentrations in subjects with impaired glucose tolerance (IGT).

Inclusion Criteria:

Men and non-pregnant women with IGT, as defined by the World Health Organization
Aged 30 years to 65 years
BMI under 40kg/m²
Serum triacylglycerols under 10mmol per L.

Exclusion Criteria:

Excluded if they were pregnant
Under 30 years or over 65 years
Did not have IGT or triacylglycerol concentrations under 10mmol per L or BMI under 40kg/m².

Description of Study Protocol:

Recruitment: Subjects were screened for IGT and then were recruited for the study
Design: Randomized controlled trial
Blinding used: Implied with measurements
Intervention: Subjects were randomly-assigned to high-carbohydrate, high-glycemic index (high-GI); high-carbohydrate, low-glycemic index (low-GI); or low-carbohydrate, high-monounsaturated fatty acid (MUFA) diets for four months
The aim was for the diets to be weight maintaining, with the high-carbohydrate diets containing 55% of energy from carbohydrate and 30% from fat and the MUFA diet containing 45%
carbohydrate and 40% fat, of which one-half was MUFAs.
Statistical analysis: Differences in the clinical variables were examined by analysis of variance (ANOVA). Significant mean effects were confirmed by using linear regression. Tukey's test was used to adjust for multiple comparisons. All statistical tests were two-tailed, with P≤0.05 taken as significant.

Data Collection Summary:

Timing of Measurements

After fasting overnight, subjects came into the nutrition center at baseline and during the last week of the study for an eight-hour metabolic profile
After baseline data were collected, subjects were assigned to one of three diets for four months
During the study, subjects were seen monthly for the collection of fasting blood samples, weight measurements and consultation with dietitians and to hand-in the three-day diet records and pick-up study foods.

Dependent Variables

Plasma glucose, insulin, triacylglycerols, free fatty acids and total cholesterol were measured by standard clinical procedures.

Independent Variables

Assignment to high-GI, low-GI or MUFA diet for four months
The aim was for the diets to be weight maintaining, with the high-carbohydrate diets containing 55% of energy from carbohydrate and 30% from fat and the MUFA diet containing 45%
carbohydrate and 40% fat, of which one-half was MUFAs.
Study foods provided
Nutrient intake from the high-GI, low-GI and MUFA diets were calculated from the food records with an in-house program that used a database based on the US Department of Agriculture food-composition tables.

Description of Actual Data Sample:

Initial N

257 individuals were screened for IGT: 44 subjects were eligible.

Attrition (Final N)

37 eligible subjects were assigned by coin toss to one of three test diets. The abstract mentions that 34 subjects completed the study.

High-GI diet: 11 subjects, two males, nine females; mean age, 58.8±4.0 years
Low-GI diet: 13 subjects, three males, 10 females; mean age, 55.2±3.0 years
MUFA diet: 11 subjects, two males, nine females; mean age, 55.8±4.0 years.

Age

30 to 65 years.

Ethnicity

Not given.

Other Relevant Demographics

Not described.

Anthropometrics

Significant differences between groups at baseline, in terms of metabolic profiles.

Location

Toronto, Canada.

Summary of Results:

Key Findings

Carbohydrate intake, as a percentage of energy, glycemic index and glycemic load in the different groups (breakfast and lunch meals combined)
- High-GI: 60%, 61 and 63
- Low-GI: 60%, 53 and 55
- MUFA: 49%, 61 and 52.
In subjects with IGT, reducing the GI of the diet for four months reduced post-prandial plasma glucose by the same amount as did reducing carbohydrate intake
Compared with the change after four months of the high-GI diet, both the low-GI and MUFA diets reduced zero- to eight-hour mean plasma glucose concentrations by 0.35mmol per L (P<0.05)
However, these two dietary maneuvers had different effects on post-prandial plasma insulin, triacylglycerols and FFAs
Mean plasma insulin was approximately 20% higher (P<0.05) and FFAs approximately 12% lower (P<0.05) after the low-GI diet than after the high-GI diet, with no significant effect of MUFA
In addition, there were significant differences in zero-to-eight-hour mean plasma triacylglycerols between the High-Glycemic Index, Low-Carbohydrate and Low-Glycemic Index Diet Groups (-0.14mmol, 0.04mmol and 0.18mmol per L, respectively) as well as body weight (-0.49±0.29kg, 0.27±0.45kg and -0.19±0.40kg, respectively, P<0.001).
Blood pressure and renal outcomes were not reported.

Author Conclusion:

We conclude that in subjects with IGT, reducing glycemic load of the diet for four months significantly reduces post-prandial plasma glucose concentrations
The same reduction in plasma glucose was achieved by reducing the GI of the diet and by reducing carbohydrate intake
However, these two dietary maneuvers had different effects on post-prandial plasma insulin, triacylglycerols and FFAs.

Funding Source:

Industry:

International Olive Oil Council

Commodity Group:

Not-for-profit

Canadian Diabetes Association

Foundation associated with industry:

Reviewer Comments:

Small numbers of subjects in groups, significant differences in metabolic profile between groups at baseline.

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?	???
2.	Was the selection of study subjects/patients free from bias?		???
	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
	2.1.	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
	2.2.	Were criteria applied equally to all study groups?	Yes
	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?	???
	2.4.	Were the subjects/patients a representative sample of the relevant population?	???
	3.	Were study groups comparable?	No
3.	Were study groups comparable?		No
	3.1.	Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT)	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?	No
	3.2.	Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline?	No
	3.3.	Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.)	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
	3.4.	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
	3.5.	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
	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.	Was method of handling withdrawals described?		No
	4.1.	Were follow-up methods described and the same for all groups?	???
	4.1.	Were follow-up methods described and the same for all groups?	???
	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%.)	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%.)	No
	4.3.	Were all enrolled subjects/patients (in the original sample) accounted for?	???
	4.3.	Were all enrolled subjects/patients (in the original sample) accounted for?	???
	4.4.	Were reasons for withdrawals similar across groups?	???
	4.4.	Were reasons for withdrawals similar across groups?	???
	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?	Yes
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?	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?	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
	5.4.	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?	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?	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?	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
	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.	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
	7.1.	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
	7.2.	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
	7.3.	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
	7.4.	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
	7.5.	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
	7.6.	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?	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?	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?	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?	No
	9.2.	Are biases and study limitations identified and discussed?	No
	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