Pediatric Weight Management

PWM: Low Carbohydrate and Low Glycemic Index Diets (2006)


Ludwig DS, Majzoub JA, Al-Zahrani A, Dallal GE, Blanco I, Roberts SB. High glycemic index foods, overeating, and obesity. Pediatrics 1999;103:e26

PubMed ID: 10049982
Study Design:
Randomized Crossover Trial
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Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:
To test the hypothesis that consumption of High-glycemic index (GI) foods induces a sequence of hormonal changes that lead to decreased availability of metabolic fuels, excessive hunger, and overeating in obese adolescent males. 
Inclusion Criteria:
  1. Pubertal boys (mean age 15.7±1.4 (SD) years
  2. Obese--defined as >120% of ideal body weight (National Center for Health Statistics [NCHS] percentiles, 1979)
  3. Healthy (assessed by physical examination and laboratory analysis--complete blood count, electrolytes, liver function tests, glycosylated hemoglobin, thyroid stimulating hormone and urinalysis)


Exclusion Criteria:

Participants were exluded from study if they were:

  1. Nonobese adolescent boys
  2. Non-healthy
Description of Study Protocol:

Recruitment --13 participants recruited to participated in study

Design--cross-over randomized study consisting of three separate 24-hour admissions (Children's Hospital, Boston) separated by a 1- to 2-week washout-period

Blinding used (if applicable)--no

Intervention (if applicable)

Study protocol:

12 obese adolescent males were randomly assigned to receive different test meals (Low-, Medium-, or High-GI meals) at 3, 24-hour admissions to the General Clinical Reseach Center (GCRC), Children's Hospital, Boston. There was a 1- to 2-week washout period between admissions.

Each admission was conducted in an identical manner. For each admission:

  • After admission at 6 pm, subjects received a standard Low-GI dinner (40% energy from carbohydrate, 30% from protein, 30% from fat; total energy 18.5% of predicted resting metabolic rate (RMR) calculated from body weight at preadmission physical examination).  A bedtime snack was also provided (same macronutrient breakdown as dinner; energy content 5% of predicted RMR).
  • At 6:45 am the following morning, after an intravenous line was placed and baseline blood samples were obtained and hunger scale measurements were taken ("not at all hungry" to "extremely hungry"). Participants received test meals at breakfast that had a Low-, Medium-, or High-GI to be consumed completely in 20 minutes.
  • Blood samples and hunger scale ratings were obtained every 30 minutes for 5 hours from the start of breakfast.
  • After 5 hours, the intravenous line was removed and a second test meal (same GI content as breakfast on that day) was provided for lunch to be consumed completely in 20 minutes.
  • After lunch, subjects were allowed out of bed and encouraged to request "ad libitum" snack meals (~22.7 mJ each) if "very hungry" (as many as desired) during the subsequent 5 hours. They could eat as much or as little as wanted to satiety. Timing before request of snack meals was recorded. Leftovers were weighed to determine amount eaten.
  • Subjects were discharged and instructed to follow usual diet between admissions.

Test meals:

Alterations in GI content were obtained through differences in food structure and sugar types. Meals were not energy restricted. The nutrient breakdown for the 3 test meals were as follows:

  • Low-GI: 40% energy from carbohydrate, 30% from protein, 30% from fat.
  • Medium-GI and High-GI: 64% energy from carbohydrate, 16% from protein, 20% from fat. The 2 test meals differed in type of oatmeal ("steel cut" for Medium-GI and "instant oatmeal" for High GI); type of sweetener (dextrose for High-GI and fructose for Medium-GI); milk (lactaid drops added to milk to increase GI of milk sugar for high-GI).
  • Energy density was similar for 3 meals (2.5 kJ/g).
  • The size of the test meals were determined individually for each subject (18.5% of predicted RMR).

The snack meals were identical for each participant (~22.6 mJ each).

Statistical Analysis

  • Repeated measures ANOVA with meal alone or meal and time as within-subjects factors.
  • Tukey's tests to adjust for multiple meal comparisons, except for fatty acids, epinephrine, and growth hormones for which only the high- and low-GI meals were compared.
  • Within-subject correlations coefficients between afternoon energy intake and hormonal and metabolic parameters.
  • Areas under the glycemic response curves were calculated using the trapezoidal rule for values above baseline.

Significance estabished at P<.05.

Data Collection Summary:

Timing of Measurements

Anthropometrics: body weight obtained during preadmission physical examination. Method not described.

Dietary: For each admission (3 total):

  • Standard low GI meal and bedtime snack after admission to the GCRC (6 pm).
  • Next day, subjects consumed identical test breakfast and lunch meals that had a low, medium, or high-GI (randomly assigned). All meals were prepared under supervision of the research dietitians and were to be consumed completely within 20 minutes.
  • 10-cm analog hunger scale rating ("not at all hungry" to "extremely hungry") was obtained before breakfast and every 30 minutes prior to lunch.
  • Following lunch, until discharge, subjects were encouraged to request "ad libitum" snack meals if "very hungry." Timing to requests following test meals were recorded and leftovers were weighed to determine amount of energy consumed at each meal request.

Laboratory (for hormonal and metabolic changes after test breakfasts)

  • Baseline: complete blood count, electrolytes, liver function tests, glycosylated hemoglobin, thryroid stimulating hormone and urinalysis.
  • Blood samples obtained every 30 minutes (intravenous line) between breakfast and lunch test meals (plasma glucose, insulin glucagon, epinephrine, serum fatty acids, growth hormone levels). 

Dependent Variables

  • Hormonal and metabolic responses: (mean plasma glucose, insulin, glucagon, epinephrine, fatty acids, growth hormone) from blood samples between breakfast and lunch
  • Perceived hunger: hunger scale ratings
  • Voluntary food intake: snack meals were used for measurement of voluntary food intake. Time between test meals and requests of snack meals and energy intake were recorded.

Independent Variables

  • 3 test meals--low-, medium-, or high-GI

Control Variables--not reported

Description of Actual Data Sample:

Initial N: 13 adolescent males

Attrition (final N): 12; one participant had recurrent difficulties establishing and maintaining intravenous access

Age: mean and SD: 15.7±1.4 y

Ethnicity: not provided

Other relevant demographics: not provided

Anthropometrics: all adolescent boys were obese (defined as >120% ideal body weight; NCHS, 1979)

Location: General Clinical Research Center (GCRC), Children's Hospital, Boston, MA

Summary of Results:

Hormonal and metabolic responses:

The hormonal and metabolic responses to the High-, Medium-, and Low-GI meals were markedly different as follows:

  • The mean area under the glycemic response curve for the High-GI meals was twice that of the Medium-GI meal and nearly fourfold that of the Low-GI meal (p<.001).
  • The mean plasma glucose concentration was lower after the High-GI meal than after the Medium-GI meal or the Low-GI meal (p=.02).
  • The insulin level was greater after the High-GI meal than after the Medium-GI meal or Low-GI meal because of the rapid absorption of glucose (p<.01).
  • Plasma glucagon level rose after the Low-GI meal but was suppressed after the Medium- and High-GI meals; likely because of the low protein content of the high-GI meal and inhibitory effects of high plasma glucose and insulin concentrations (p<.01).
  • Serum fatty acids were suppressed to a greater extent after the High-GI meal compared with the Low-GI meal (p<.05).
  • Higher concentrations of the hormones epinephrine (p<.05) and growth hormone (p=.05; not significant, respectively) after the High-GI meal relative to the Low-GI meal.

Perceived hunger and voluntary snack meal timing and energy intake:

  • Perceived changes in hunger after test breakfasts (ratings of hunger) were greater at all 30 minute time periods for the High-GI breakfast, compared with the Low-GI breakfast, with Medium-GI yielding intermediate scores.
  • On average, participants consumed 53% more energy after High-GI meals than after the Medium-GI meals (5.8 mJ and 3.8 mJ, respectively; p<.05) and 81% more total energy after High-GI meals than after Low-GI meals (5.8 mJ and 3.2 mJ, respectively; p=.01).
  • Mean time to the first snack meal request was 2.6 hours for the High-GI meals, 3.2 hours for the Medium-GI meals, and 3.9 hours for the Low-GI meals (High- versus Low-Gi meals; p=.01; High-versus Medium-GI meals; not significant).


  • Only baseline heights and weights were reported; no follow-up on weight status during study.
Author Conclusion:

The results of this study demonstrated that meals containing varying GI content had markedly different effects on metabolism and hormones, perceived hunger, and subsequent food intake in overweight adolescent males. In comparison to Low-GI meals, High-GI test meals resulted in higher postprandial serum glucose and insulin levels, lower glucagon levels, and lower serum fatty acid levels. In addition, longer time to request voluntary meals after Low-GI meals (breakfast and lunch) was observed. Voluntary energy intake after High-GI meals was 53% greater than after Medium-GI meals and 81% greater than after Low-GI meals.

"We recognize that this study evaluated only the acute effects of Low-GI meals; the effectiveness of Low-GI diet in promoting long-term weight loss is unknown. Long-term dietary intervention studies are necessary to resolve this question. Moreover, reductions in dietary GI may also have beneficial effects on serum lipids, risk of diabetes mellitus, and other diseases associated with hyperinsulinemia."

Funding Source:
Government: NHLBI
Reviewer Comments:


  • No blinding indicated
  • Study only evaluated the acute effects of Low-GI meals; not long-term. may not reflect long-term effects of Low- or High-GI diets such as effects on body weight   
  • Limited generalizability; only male adolescent subjects were included in study (females, different age groups?)


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? No
  2.4. Were the subjects/patients a representative sample of the relevant population? ???
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.) 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? 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? N/A
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? 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
  7.1. 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? N/A
  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)? 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? 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