PWM: Individual Child Counseling (2006)


Ebbeling CB, Leidig MM, Sinclair KB, Hangen JP, and Ludwig DS. A Reduced–Glycemic Load Diet in the Treatment of Adolescent Obesity. Arch Pediatr Adolesc Med 2003;157:773-779.

PubMed ID: 12912783
Study Design:
Randomized Controlled Trial
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Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:

To compare the effects of an ad libitum, reduced–glycemic load (GL) diet with those of an energy-restricted, reduced-fat diet in obese adolescents.

The aims of this work were (1) to develop a reduced-GL diet for use in an adolescent population; (2) to determine whether adolescents following this diet will successfully achieve long-term reduction of GL; and (3) to compare the long-term effects of a reduced-GL diet with those of a conventional reduced-fat diet in a pilot study involving obese adolescents.

Inclusion Criteria:

Obesity defined as BMI exceeding sex-and-age-specific 95th percentiles, age 13-<22 years.

Exclusion Criteria:

Subjects free of major medical illness, as assessed by means of physical examination and screening laboratory tests (measurement of kidney and liver enzymes, thyrotropin, glycosylated hemoglobin, and fasting plasma glucose levels and urinalysis).

Description of Study Protocol:

The reduced-GL prescription emphasized selection of carbohydrate-containing foods (eg nonstarch vegetables, fruits, legumes, nuts and dairy) that are characterized by a low to moderate GI. Patients were instructed to balance consumption of carbohydrates with protein and fat at every meal and snack.  The prescription was not energy restricted.  Rather, subjects were advised to eat to satiety and to snack when hungry.  The targeted proportion of energy from carbohydrate and fat were 45% to 50% and 30% to 35%, respectively, with the remainder from protein.  An ad libitum approach was used in light of preliminary evidence that suggests greater satiety and decreased voluntary energy intake occurs among children and adolescents consuming reduced-GL diets.

The reduced-fat prescription was based on current recommendations for weight loss and diabetes prevention, with emphasis on limiting dietary fat intake and increasing the intake of grains, vegetables, and fruits.  Meal plans were designed to elicit a negative energy balance of 250 to 500 kcal/d.  Energy requirements were estimated using the Harris-Benedict equation, with an activity factor of 1.5 and consideration of baseline dietary intake.  Subjects were counseled to obtain 55% to 60% of energy from carbohydrates, 25% to 30% from fat, and the remainder from protein.

Social cognitive theory provided a conceptual framework for the educational and behavioral components of treatment that was consistent between intervention groups.  Counseling focused on enhancing self-efficacy for dietary change using the concepts of behavioral capability (knowledge and skill) and self-control.  Patient expectations (anticipated outcomes), expectancies (values ascribed to outcomes), and perceptions of environmental influences were discussed during treatment sessions.

Written materials included topic modules, food choice lists, and select-a-meal menu.  The topic modules were the primary mechanism for presenting nutrition intervention messages and facilitating self-assessment, goal setting, and problem solving.  These modules were designed to promote dialogue between the patient and study dietitian.  Food choice lists were used to enhance practical application of intervention messages presented in the topic modules.  For the experimental group, lists corresponded to food groups delineated by a reduced-GL food pyramid.  In contrast, for the conventional group, the lists corresponded to the diabetes food pyramid and were presented as an exchange system.  The select-a-meal menu contained recipes and ideas for meal planning to complement the food choice lists.  One topic module was devoted to physical activity, with subjects in both groups receiving information based on current recommendations.  Nutrition bars were offered to subjects in the experimental (Balance Bar; kindly provided by Kraft Foods, Inc., Northfield, Ill) and conventional groups (Nature Valley Granola Bar; General Mills, Inc., Minneapolis, Minn) for occasional use as snacks.

Data Collection Summary:

Total body mass and fat mass were measured by dual-energy x-ray absorptiometry using hologic instrumentation (Model QDR 4500; Hologic, Inc., Bedford, Mass). Height was measured using a wall-mounted stadiometer (Holtain Limited, Crymych, Wales).  A blood sample was drawn by means of venipuncture after a 12-hour overnight fast.  Plasma glucose level was measured using a Hitachi analyzer (Model 917, Roche Diagnostics, Indianapolis, Ind), and serum insulin level was measured using an Elecsys system (Model 2010, Roche Diagnostics).  We used homeostasis model assessment (HOMA) to estimate insulin resistance by means of the following equation: (Fasting  serum insulin level (in microunits per milliliter] X fasting plasma glucose level [in millimoles per liter] ) /22.5.  This index has been used previously for assessing insulin resistance in youth, with higher values indicating lower insulin sensitivity.

Description of Actual Data Sample:

Sixteen obese adolescents aged 13 to 21 years.

Summary of Results:

Fourteen subjects finished the study (7 per group), yielding a completion rate of 87.5%. There were no group differences in session attendance, with subjects in the experimental and conventional groups completing 9.4 +/- 0.6 of the 12 planned sessions during the intervention period.  All 14 subjects attended the 2 scheduled sessions during the follow-up. 

Baseline Measures

At baseline, we found no differences between the experimental and conventional groups for:

  • age (16.9±1.3 vs. 15.3±0.9 years; P=.33),
  • body mass (103.5±6.0 vs. 104.7±4.8 kg; P=.88),
  • height (171.6±3.3 vs. 167.9±2.1 cm; P=.37),
  • BMI (34.9±1.0 vs 37.1±1.2; P=.21), and
  • HOMA estimation of insulin resistance (3.5±0.7 vs. 4.3±0.7; P=.43). 

However, fat mass was lower for the experimental group compared with the conventional group (38.8±2.6 vs. 48.5±3.0 kg; P=.03).

Dietary Intake Outcomes

The GL decreased for the experimental group (0-6 months, P=.005; 0-12 months; P=.007) and did not change significantly for the conventional group.  Dietary fat decreased for the conventional group (0-6 months, P=.01; 0-12 months, P=.03) and tended to increase for the experimental group (0-6 months, P=.06).  Carbohydrate intake decreased for the experimental group (0-6 months, P=.03; 0-12 months, P=.07).

Anthropometric Outcomes

BMI (P=.03) and fat mass (P=.02) decreased in the experimental group from 0 to 12 months, and neither outcome changed significantly in the conventional group.  At 12 months, BMI (-1.3±0.7 vs. 0.7±0.5; P=.02) and fat mass (-3.0±1.6 vs. 1.8±1.0 kg; P=.01) had decreased significantly more in the experimental compared with the conventional group.  These results were materially unchanged in intention-to-treat analyses (BMI, -1.2±0.7 vs. 0.6 ±0.5 [P=.02]; fat mass, -2.6±1.5 vs. 1.6±0.9 kg [P=.01]. 

Of interest, there was no weight regain between 6 and 12 months for the experimental group.  Insulin resistance, as assessed by means of HOMA, increased significantly less in the experimental compared with the conventional group during the intervention period (-0.4±0.9 vs. 2.6±1.2; P=.02), and statistical adjustment for BMI did not materially alter this result (P=.03).

Bivariate linear regression analysis was performed using dietary GL or fat intake during the intervention period as the independent variable and change in body fat from 0 to 6 months as the dependent variable.  Change in GL was a strong predictor of this study outcome, explaining about half of the variance in both groups combined (R2 = 0.51; P=.006).  In contrast, change in dietary fat was not significantly associated with change in body fat (R2 = 0.14; P=.22).

Author Conclusion:

An ad libitum reduced-GL diet appears to be a promising alternative to a conventional diet in obese adolescents. Large-scale randomized controlled trials are needed to further evaluate the effectiveness of reduced-GL and –glycemic index diets in the treatment of obesity and prevention of type 2 diabetes.

Our results suggest that reducing dietary GL may have greater benefits than reducing dietary fat when treating adolescent obesity to lower the risk for type 2 diabetes mellitus. Although findings must be considered preliminary, this study provides relevant pilot data to inform future research.  Large-scale randomized controlled trials are needed to evaluate the effectiveness and public health applications of reduced-Gl and GI diets.
Funding Source:
Government: NIDDK, NIH
University/Hospital: Children’s Hospital Boston, Harvard Medical School
Foundation associated with industry:
Reviewer Comments:

Very well-designed study.

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? ???
  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.) ???
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? ???
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? ???
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? ???
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? ???
  5.5. In diagnostic study, were test results blinded to patient history and other test results? ???
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? 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
  6.5. 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? ???
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)? 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
  8.7. If negative findings, was a power calculation reported to address type 2 error? Yes
9. Are conclusions supported by results with biases and limitations taken into consideration? Yes
  9.1. Is there a discussion of findings? Yes
  9.2. 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