EAL

DM: Carbohydrates (2007)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

To determine whether glycemic index differentially affects improved glucose and lipid profiles observed during weight loss in overweight subjects previously diagnosed with type 2 diabetes with variable glucose tolerance.

Inclusion Criteria:

diagnosis of type 2 diabetes in the last 10 years
overweight
required only dietary treatment

Exclusion Criteria:

treatment with oral hypoglycemic agents or insulin
renal or liver disease

Description of Study Protocol:

Recruitment : through public advertisement

Design: Randomized Controlled Trial

4-week run-in period on weight loss diet similar in composition to typical Australian diet
8 weeks on allocated high- or low-GI diet
subjects asked not to consume alcohol while on study
subjects asked to maintain usual exercise patterns while on study

Blinding used (if applicable): blinding to diet not possible

Intervention (if applicable)

Diet

energy restriction to 1500 kcal/d
first 4 weeks: 32% fat, 17% saturated fat, 50% carbohydrate, 20% protein
intervention period of 8 weeks
- both diets 60% carbohydrate, 15% fat, 20% protein
- Low GI diet: GI score of 43
- high GI diet: GI score of 75
- GI of diet was reduced using wholegrain foods; no legumes were included in low-GI diet

Statistical Analysis

data from two consecutive visits at weeks 0, 4, 8, and 12 were averaged for statistical analysis.
data was analyzed at weeks 0 and 4 for all subjects together and then at weeks 4 and 12 to test the differential effects of GI with repeated measures GLM and age, gender, BMI, saturated fat intake and diabetes status as cofactors
one-way ANOVA was used to test baseline differences and differences in energy and nutrient composition
post hoc analysis was performed using Bonferonni where necessary
correlations performed using Pearson correlation coefficients
chi-square analysis used to determine the distribution of gender and diabetes status by high-and low-GI diet

Data Collection Summary:

Timing of Measurements

fasting venous blood samples taken on two consecutive mornings at week 0 and at weeks 4, 8, and 12
weight and blood pressure measured at each visit
upper arm, waist, hip, circumferences; biceps, triceps, subscapular and supra-iliac skinfolds measured at weeks 0 and 12
HbA1c, 24-hour urine collection, and 3-hour OGTT measured at weeks 0, 4, and 12

Dependent Variables

weight
blood pressure
serum lipids
glycemic control

Independent Variables

subjects provided with breads, cereals, biscuits and some protein foods, approximately 60% of energy intake, every week
subjects attended diet consultations every two weeks tor assessment of compliance
subjects completed 3-day food records every two weeks

Control Variables:

age
gender
BMI
saturated fat intake
diabetes status

Description of Actual Data Sample:

Initial N: 56 subjects, 26 male and 30 female, matched on the basis of gender, age, BMI, fasting plasma glucose, triglycerides and total cholesterol concentrations before being randomized

Attrition (final N): 45 subjects, 23 male and 22 female included in the final analysis

Age: 56.0±2.0

Ethnicity: Caucasian

Other relevant demographics:

fasting glucose: 7.07±0.46
HbA1c: 6.74±0.29%

Anthropometrics: BMI 34.2±1.0. Pre-study subject characteristics were not significantly different between groups.

Baseline glucose tolerance:

12 men and 13 women classified with low glucose tolerance ( 2-hours post glucose ingestion venous plasma glucose sample was > 11.1 mmol/l
10 subjects had median glucose tolerance, >7.8 mmol/l
10 subjects had high glucose tolerance <7.8 mmol/l

Location: Australia

Summary of Results:

Clinical and metabolic characteristics of subjects at week 12

Variables	High GI Diet Group Week 12	Low GI Diet group Week 12	Between Treatments
			Change Weeks 4-12	P-Value
Weight, kg	88.4±2.6*#	87.3±3.3 *#	0.29	0.876
Systolic BP, mmHg	125±3*#	130±3* #	3.3	0.430
Diastolic BP, mmHg	79±2*#	77±2* #	3.5	0.123
Glucose, mmol/l	6.08±0.25*#	6.47±0.39*#	0.12	0.309
AUC, mmol/min/l	10.2±0.9*	11.8±1.1*	0.35	0.742
HbA1c, %	6.06±0.19*#	6.65±0.28 *#	0.31	0.170
Total-C, mmol/l	4.75±0.18*#	5.01±0.17* #	0.17	0.221
LDL, mmol/l	2.91±0.17*#	2.91±0.15 *#	0.20	0.102
HDL,mmol/l	1.12±0.08	1.26±0.08	0	0.935
Triglyceride, mmol/l	1.60±0.11*	1.84±0.14*	0.06	0.828
Total-C/HDL ratio	4.38±0.23*#	5.28±0.48* #	0.20	0.621

* P<0.005 from baseline

# P<0.05 from week 4

Other Findings

Author Conclusion:

This study suggests that altering the glycemic index of high-carbohydrate energy-restricted diets does not impact on the improvement in glycemic control that is observed normally during energy restriction.

However, low glycemic index, high-carbohydrate diets may be slightly better in improving glycemic control and lipoprotein metabolism in subjects who have low glucose tolerance, but this clearly needs confirmation.

Funding Source:

Reviewer Comments:

This study separates the effects of weight loss from those of GI value of the diet.

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?		Yes
	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.)	Yes
	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?	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
	6.8.	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?		???
	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)?	No
	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?	No
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