EAL

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

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

To investigate whether a low-glycemic index (GI) meal replacement (LMR) produced similar metabolic, hormonal, and satiety responses in overweight adolescents as a low-GI whole-food (LWM) as demonstrated by Ludwig et al. (1999), when compared with a moderately high-GI meal replacement (HMR).

Inclusion Criteria:

Screening included measurement of height and weight for calculation of body mass index (BMI), a physical examination, self-reported assessment of puberty, and blood tests--complete blood count, electrolytes, liver function tests, thyroid-stimulating hormone, and glycosylated hemoglobin. Female participants were admitted during the first 10 days after the start of their menstrual cycle.

Inclusion criteria included:

12 to 18 years of age
BMI >= 95th percentile for age and sex or >30 (kg/m²)
good health status, other than overweight (assessed from screening physical exam and blood tests)

Exclusion Criteria:

Exclusion criteria included:

medical history other than overweight
taking medication known to affect metabolism
for females: if pregnant or had history of pregnancy

Description of Study Protocol:

The study was conducted in the General Clinical Research Center (GCRC) at the University of Utah.

Recruitment -- 16 (8 females and 8 males) were recruited to participate in study

Design--randomized, cross-over design, modeled after Ludwig et al (1999); 3 separate 24-hour admissions separated by 3 day minimum washout period.

Blinding used (if applicable)--No

Intervention (if applicable)

Participants were admitted to the GCRC for 3, 24-hour admissions; separated by a 3-day minimum wash-out period. Each admission was handled identically.

Study protocol:

Participants were admitted at 5 pm. Height, weight, and blood pressure were measured.
A low-GI (45% carbohydrate, 30% fat, 25% protein) dinner and bedtime snack were served, and participants were encouraged to consume all food served.
Between 6:30 and 7 am, a peripheral indwelling venous catheter for blood draws was placed and a baseline blood sample was drawn.
A hunger rating scale was completed and a randomly assigned breakfast was served. Each participant was encouraged to consume all food within 15 minutes.
Additional blood samples and hunger scale ratings were obtained at 15-, 30-, 60-, 120-, 180-, and 240- minutes after breakfast was served.
Four hours after breakfast, the catheter was removed and lunch was provided (identical to test meal at breakfast), to be consumed within 15 minutes.
After lunch, participants were encouraged to request "ad libitum" snack platters when "very hungry." Participants were encouraged to eat to satiety. Leftovers (after 30 minutes) were weighed to determine amount eaten.
Participants were discharged 5 hours after lunch and told to follow usual eating and physical activity patterns.

Study test meals:

One of 3 test meals--Low GI Meal Replacement (LMR), High GI Meal Replacement (HMR), or Low GI Whole Food (LWM) was provided for breakfast and lunch (randomly assigned). Meals were not energy-restricted. GI value different for 3 test meals; otherwise diets similar in macronutrient content.
Energy content of meals was based on the estimated resting energy expenditure (REE) of each participant based on height and weight using the gender-specific Schofield equations.
The LMR included a powdered drink supplement served with a nutrition bar; the macronutrient content was 45% carbohydrate, 29% fat, and 26% protein with a GI value of 28.
The HMR also contained a powdered drink supplement (with 2 drops of Lactaid added) and nutrition bar; the macronutrient content was 43% carbohydrate, 32% fat, and 25% protein with a GI value of 62.
The LWM contained scrambled eggs, cheese, ham, apple, and skim milk. The macronutrient content was 45% carbohydrate, 30% fat, and 25% protein with a GI value of 43.
The snack platters were identical for each participant; requests based on hunger scale rating.

Statistical Analysis

Participant responses were evaluated using repeated-measures analysis of variance (ANOVA) with meal alone and meal and time as within participant factors and diet sequence order as between participant categorical factor to determine any effect of diet sequence order
One-way ANOVA was used to compare incremental areas under the curve for glucose, insulin, glucagon, and fatty acids for each test meal
Pair-wise comparisons between the 3 test meals using a paired sample Student t test
Friedman 2-way ANOVA for energy consumed from the snack platters

P<.05 was considered statistically significant

Data Collection Summary:

Timing of Measurements

Anthropometrics:

Height and weight were measured for the calculation of BMI at the beginning of each admission

Laboratory and clinical:

Blood pressure was measured at start of each admission
Blood was collected at each admission and analyzed for: glucose, insulin, glucagon, insulin-like growth factor (IGF-1), insulin-like binding protein (IGFBP-3), and fatty acid

Perceived satiety:

Hunger rating scales during each admission
Ad libitum food intakes

Dependent Variables

Metabolic and hormonal responses (glucose, insulin, glucagon, insulin-like growth factor [IGF-1], insulin-like binding protein [IGFBP-3], and fatty acid)
Percieved satiety (assessed by hunger scales between morning and noon meals
Voluntary food intake: (assessed by time to and amount of additional voluntary food intake between noon meals and discharge)

Independent Variables

3 test meals: Low GI Meal Replacement, High GI Meal Replacement, or Low GI Whole Food

Control Variables--not presented

Description of Actual Data Sample:

Initial N: 16 adolescents; 8 females and 8 males

Attrition (final N): all 16 participants completed the study

Age: At baseline:

Females: 14.3 ± 2.1 years
Males: 13.6 ± 1.5 years

Ethnicity: not presented

Other relevant demographics: N/A

Anthropometrics: At baseline:

Females: 35.2 ± 2.4
Males: 33.7 ± 5.2

Location: at GCRC at the University of Utah

Summary of Results:

Metabolic and Hormonal changes:

Changes from baseline glucose and insulin responses were significantly different between the test meals:

The incremental areas under the curve for glucose were almost twice as large after the High GI Meal Replacement compared with the Low GI Meal Replacement and Low GI Whole Food; 46% and 43% lower after the Low GI Meal Replacement and Low GI Whole Food, respectively, compared with the High GI Meal Replacement (p<.001)
The incremental area under the curve for insulin was significantly lower after both the Low GI Meal Replacement (~1/3; 36%) and Low GI Whole Food (~1/2; 51%) compared with the High GI Meal Replacement (p<.05)
No significant differences existed between the 3 test meals for glucagon, fatty acids, IGF-1, and IGFBP-3

Percieived satiety (assessed on basis of 3 indices: hunger scales between morning and noon meals, time to snack platters, and voluntary energy intake from snack platters after noon meals until discharge:

Snack platters were requested sooner after the High GI Meal Replacement compared with the Low GI Meal Replacement and Low GI Whole Food; Low GI Meal Replacement vs. High GI Meal Replacement (mean 3.9 vs 3.1 hours, respectively; p<.01); but not significant Low GI Whole Food vs High GI Meal Replacement and Low GI Meal Replacement vs Low GI Whole Food
However, once snack platters were requested, voluntary energy intake did not differ significantly between test meals

BMI:

Although baseline BMIs were presented, no follow-up BMIs were presented in article.

Author Conclusion:

Results of this study showed significantly lower glucose and insulin responses in obese adolescents after the ingestion of both the Low GI Meal Replacement and Low GI Whole Food when compared with the High GI Meal Replacement. In addition, prolongation of satiety after the Low GI Meal Replacement, based on time to request snack platters, was observed. However, voluntary snack energy intake did not differ for 3 test meals.

"We speculate that the prolonged satiety associated with low GI foods may prove an effective method for reducing calorie intake and achieving long-term weight control. Additional studies examining the effects of long-term low-GI diet are needed."

Funding Source:

Government:

National Center for Research Resources

Industry:

USANA

Other:

Reviewer Comments:

Limitations:

No blinding indicated
The hunger rating scale utilized is a subjective assessment tool; obese individuals may respond differently to external cues of hunger than nonobese individuals
Metabolic and hormonal responses and perceived satiety were evaluated for 3 test meals (acute responses) but not long-term weight changes. Although the authors stated that height and weight were measured at each admission, only the baseline BMI values were presented. Thus, it is not clear how the authors could conclude that the results of this study may be related to "achieving long-term weight control."
? generalizability; participants were overweight adolescents

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%.)	N/A
	4.3.	Were all enrolled subjects/patients (in the original sample) accounted for?	Yes
	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?		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?	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?	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