AWM: Low Glycemic Diets (2006)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
To evaluate the effect of a high-dairy diet on weight loss and body fat and investigate whether the effect would be enhanced with a high-fiber, low-glycemic index diet. 
Inclusion Criteria:
Men and women aged 25 - 70 with stable weight (BMI 30 to 40) over the previous 6 months.
Exclusion Criteria:
Subjects who were lactose intolerant, pregnant, had history of eating disorder, took calcium supplements (and were unwilling or unable to discontinue them for the study), took medication for diabetes or weight loss, took antidepressant agents associated with weight gain, or had digestive disorders that would prohibit following a high-fiber diet were not eligible.
Description of Study Protocol:

Recruitment

Subjects recruited from October 2001 through April 2002 by placing posters near employee elevators in the clinic and hospital.

Design

Randomized controlled trial.

Blinding used (if applicable)

Neither subjects nor dietitian were blinded to assigned diet.

Intervention (if applicable)

3 diets providing a calorie deficit of 500 kcals/day.  Diet 1 was 30% fat, 20% protein, and 50% carbohydrate, with an average level of calcium and fiber, 2 dairy servings.  Diet 2 was the same as Diet 1 except 4 dairy servings were included, at least 2 being milk.  Diet 3 was the same as Diet 2 except with an increased amount of fiber (through additional whole grains, fruits and vegetables) and a reduction in glycemic index (foods with a glycemic index >100 were discouraged). 

Statistical Analysis

Statistician generated the computer randomization algorithm stratified by sex.  Distributions were characterized by percentages, means and standard deviations.  Differences between baseline and end-of-study measurements were assessed using the Wilcoxon rank sum test.  Differences among groups were determined by the Kruskal-Wallis test.  Non-parametric tests were used because many of the factors measured were highly skewed.  Three analyses were performed:  an intention-to-treat analysis with the last available value carried forward, a completer's analysis (those completing the trial) and an adherer's analysis (all who adhered to exercise guidelines and were rated as adherent by the dietitians 75% of the weeks in the study).  Study was designed to have 80% power to detect a difference in means of 3.1 kg, assuming a common standard deviation of 3.8 using one-way ANOVA and a 20% dropout rate, resulting in 24 in each group.

Data Collection Summary:

Timing of Measurements

Subjects completed a 2-week weight maintenance run-in phase and then randomized to 1 of 3 diets for 48 weeks.  Most variables measured at beginning and at end of study.  Weight and waist-to-hip ratio measured at beginning, 12, 24 and 36 weeks.  REE and body fat were measured at beginning, 24 weeks, and at end of study.

Dependent Variables

  • Body weight
  • Body fat and trunk fat by DXA scan
  • Waist circumference measured at umbilicus
  • Hip circumference measured at widest point of the hip/buttocks area with the tape measure parallel to the floor 
  • Fasting lipid profile
  • Fasting glucose and insulin
  • 2-hour glucose and 2-hour insulin
  • High-sensitivity C-reactive protein
  • Leptin measured by the Human Leptin double antibody radioimmunoassay kit
  • Resting energy expenditure by indirect calorimetry

Independent Variables

  • 3 dietary interventions - all 500 kcal/day deficits from BEE and 40% activity factor.  Meal plans based on calorie level using ADA exchanges.  Subjects bought own food.  Subjects completed a daily food diary and recorded minutes of exercise which was reviewed weekly with the dietitian.  Subjects who adhered to the plan were seen biweekly in the second half of the study, others continued to be seen weekly.  Harris-Benedict equation recalculated at 12, 24, and 36 weeks and subjects given new caloric goals to further weight loss.  Food diaries were analyzed at weeks 11, 23, 35 and 47 for 2 weekdays and 1 weekend day using the Food Processor. 

Control Variables

 

Description of Actual Data Sample:

Initial N: 90 obese subjects enrolled.

Attrition (final N):  72 completed the study (final dropout rate of 20%).  Dropouts were distributed unevenly across the groups:  2 due to pregnancy, 1 immediately dropped out, 1 gained weight, and remainder were unable to comply with weekly dietitian visits and food records.  53 subjects were compliant with diet and exercise requirements more than 75% of the time (adherers).

Age:  Standard diet:  42.0 +/- 8.8 years (25 female, 4 male), High Dairy:  41.2 +/- 9.3 years (26 female, 4 male), High Fiber/High Dairy:  41.1 +/- 8.6 years (26 female, 5 male)

Ethnicity:  Not mentioned

Other relevant demographics:  Not mentioned

Anthropometrics There were no significant differences in any of the baseline parameters among the 3 groups.

Location: Minnesota

 

Summary of Results:

 

Standard Diet High Dairy High Fiber/High Dairy P-value

Intention-to-treat weight loss (kg)

9.1 +/- 7.0 (n=29) 8.8 +/- 7.5 (n=30) 8.8 +/- 7.9 (n=31) 0.88
Adherer weight loss (kg) 11.0 +/- 6.9 (n=18) 11.2 +/- 5.9 (n=18) 11.9 +/- 7.8 (n=17) 0.91
Completer weight loss (kg) 10.0 +/- 6.8 (n=26) 11.8 +/- 6.1 (n=22) 10.6 +/- 7.9 (n=24) 0.45
Fat loss by DXA (kg) 7.5 +/- 6.6 9.0 +/- 6.0 8.5 +/- 7.8 0.58
Trunk fat loss by DXA (kg) 4.4 +/- 3.9 4.7 +/- 3.9 4.9 +/- 4.6 0.95
Change in waist circumference (cm) 8.8 +/- 6.3

11.6 +/- 6.1

11.0 +/- 7.6

0.34

Change in hip circumference (cm)

7.1 +/- 6.6

8.9 +/- 4.3

8.5 +/- 6.6

0.18

Other Findings

Significant weight and fat loss occurred with all 3 diets.  There was no significant difference in calories prescribed, caloric intake, or exercise minutes during the study among the 3 groups. 

Subjects achieved a 9% weight loss over the 48-week period using the intention-to-treat method (completers lost 11% of body weight, and adherers lost 12%).  There were no significant differences among groups in body fat loss, trunk fat loss, change in waist circumference, or change in hip circumference.

A diet with 1400 mg calcium did not result in greater weight loss (11.8 +/- 6.1 kg) or fat loss (9.0 +/- 6.0 kg) than a diet with 800 mg calcium (10.0 +/- 6.8 kg weight loss, 7.5 +/- 6.6 kg fat loss).

A diet with 1400 mg calcium, increased fiber content and fewer high-glycemic index foods did not result in greater weight loss (10.6 +/- 6.8 kg) or fat loss (8.5 +/- 7.8 kg) than the standard diet with 800 mg calcium.

Lipid profile, high-sensitivity C-reactive protein, leptin, fasting glucose, and insulin improved significantly, but there were no significant differences between the experimental diets and the control diet.

Author Conclusion:
In summary, we found no evidence that diets higher than 800 mg calcium in dairy products or higher in fiber and lower in glycemic index enhance weight reduction beyond what is seen with calorie restriction alone.  A diet high in dairy products (whether or not it was also high in fiber and lower in glycemic index) did not enhance weight loss.  Further work needs to be done to compare diets low in dairy products (400-600 mg daily calcium) with diets that are moderate (800-1000 mg) and high (1200-1400 mg) in dairy products.  This study indicates that high-dairy (vs. moderate dairy) and low-glycemic index diets should not be accepted as effective without further evidence from long-term randomized trials. 
Funding Source:
University/Hospital: Beth Isreal Hospital, Joslin Clinic, Columbia University
Reviewer Comments:

Long term study.  Relatively low dropout rate.

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? ???
  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? 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? 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