AWM: Low Glycemic Diets (2006)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
To evaluate whether a 5-week low-glycemic-index diet versus a high-glycemic index diet can modify glucose and lipid metabolism as well as total fat mass in nondiabetic men.
Inclusion Criteria:
Moderately overweight nondiabetic men.
Exclusion Criteria:
Subjects with abnormal renal, hepatic, or thyroid function were excluded.  None of the subjects was taking any drug that might affect glucose, insulin or lipid metabolism.
Description of Study Protocol:

Recruitment

Not described.

Design

Randomized Controlled Crossover Trial.

Blinding used (if applicable)

Not applicable.

Intervention (if applicable)

Men were allocated to 5 weeks of an LGI or HGI diet separated by a 5 week washout interval.

Statistical Analysis

The validity of the crossover design was tested by ANCOVA of the baseline results of the second period, with the baseline results of the first period as the covariable and the treatment of the first period as the main factor.  The effects of the 2 diets were compared by a multiple ANOVA followed by a post hoc test (least significant differences test).  The main factors considered in the analysis were the type of diet, the time of assay, and the order of diets.  To analyze acute effects, we compared the effects of 1 day LGI to those of 1-day at beginning of study period.  To analyze chronic effects, we compared the effects after 5 weeks.  The dietetic evaluations at beginning and end of each period were compared 2 x 2 with a Student's paired t test.

Data Collection Summary:

Timing of Measurements

Before the beginning of the study, all subjects were instructed to maintain their usual lifestyle during the experimental period.  Patients were randomly allocated to 2 periods of 5 weeks of LGI or HGI in crossover design, separated by 5 week washout period.  At beginning and end of each diet period, subjects were hospitalized for 2 days after an overnight fast.

Dependent Variables

  • Abdominal subcutaneous adipose tissue obtained by needle biopsy
  • Fasting blood samples analyzed for plasma glucose, insulin, lipids, plasma fructosamine, leptin,HDL, Apo-A1 and Apo-B
  • Body lean and fat mass distributions measured by DEXA
  • Fasting blood samples taken at 5-min intervals to measure insulin sensitivity and secretion by the homeostasis model assessment (HOMA)
  • RNA from adipose tissue obtained by using RNeasy total RNA kit and genes were studied

Independent Variables

  • In the LGI period, carbohydrate items with GI < 45% were recommended, whereas foods with GI > 60% were recommended during HGI period.  Subjects were provided a list of recommended daily intake of commonly used foods and substitution lists.  GIs ascribed to foods used were taken from published data or unpublished French work.  Subjects met for individual counseling with an RD concerning food intake - prescribed individually based on 3 day food records.  To assess compliance, subjects were asked to complete a food diary for the last 7 days of each dietary period.

Control Variables

 

Description of Actual Data Sample:

Initial N: 11 men

Attrition (final N):  11 men

Age: 46 +/- 3 years

Ethnicity: Not mentioned

Other relevant demographics: BMI 28 +/- 1

Anthropometrics (e.g., were groups same or different on important measures)

Location: France

 

Summary of Results:

 

HGI Baseline HGI 5 Weeks LGI Baseline

LGI 5 Weeks

Fasting total cholesterol (mmol/l) 5.52 +/- 0.42 5.30 +/- 0.39 5.30 +/- 0.27 4.90 +/- 0.38
Total fat mass (kg) 19.54 +/- 1.52

19.52 +/- 1.57

19.27 +/- 1.69

18.75 +/- 1.59

Trunk fat (kg) 9.32 +/- 0.86

8.92 +/- 0.88

8.70  +/- 0.93

8.41 +/- 0.86

Other Findings

Results of the 7-day dietary records were unchanged at the end of the 2 dietary periods with regard to total daily energy (2462 +/- 75 vs 2204 +/- 65 kcal for HGI vs LGI), macronutrients (carbohydrate:  42 +/- 1 vs 39 +/- 1% of energy, protein:  18 +/- 1 vs 20 +/- 1% of energy, fat:  37 +/- 1 vs 38 +/- 1%) and alcohol intake.

The main difference between the 2 diets was the calculated GI (71.3 +/- 1.3 vs 41.0 +/- 1.0% for HGI vs LGI, P < 0.0001).  An increase in the fiber content after the LGI diet was also found (19 +/- 1 vs 31 +/- 2 g, P < 0.0001).

Body weight was comparable between the end of the HGI and LGI periods (86.5 +/- 2.7 vs 85.7 +/- 2.9 kg).

The LGI diet resulted in lower postprandial plasma glucose and insulin profiles and areas under the curve than the HGI diet.

5 weeks of the LGI diet tended to decrease fasting total cholesterol (P = 0.065) as well as Apo-B (P = 0.076).

A 5-week period of the LGI diet lowered plasma triacylglycerol excursion after lunch (AUC, P < 0.05 LGI vs HGI).

These modifications were associated with a decrease in the total fat mass by ~700 g (P < 0.05) and a tendency to increase lean body mass (P < 0.07) without any change in body weight.

This decrease in fat mass was accompanied by a decrease in leptin, lipoprotein lipase, and hormone-sensitive lipase RNAm quantities in the subcutaneous abdominal adipose tissue (P < 0.05).

Author Conclusion:
We concluded that 5 weeks of an LGI diet ameliorates some plasma lipid parameters, decreases total fat mass, and tends to increase lean body mass without changing body weight.  These changes were accompanied by a decrease in the expression of some genes implicated in lipid metabolism.  Although the HGI diet was not associated with increased food intake and body weight, in the conditions of the present study, the possibility cannot be excluded that these parameters could be increased after longer periods.  Such a diet could be of benefit to healthy, slightly overweight subjects and might play a role in the prevention of metabolic diseases and their cardiovascular complications.
Funding Source:
Government: INSERM (France)
Industry:
Danon Vitapole, Nestle, Delessert, Benjamin Delessert
Food Company:
University/Hospital: Pierre and Marie Currie University (France),
Reviewer Comments:
Only 5 weeks per diet period, small number of subjects.  Compliance checked through food diaries.
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? ???
  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? ???
  2.4. Were the subjects/patients a representative sample of the relevant population? ???
3. Were study groups comparable? N/A
  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? N/A
  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? 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? ???
  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? ???
  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? ???
  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