Adult Weight Management

AWM: Low Carbohydrate Diet (2006)


Landers P, Wolfe MM, Glore S, Guild R, Phillips L. Effect of weight loss plans on body composition and diet duration. J Okla State Med Assoc. 2002 May;95(5):329-31.

PubMed ID: 12043107
Study Design:
Randomized Controlled Trial
A - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:
  1. Examine the effects of a low carbohydrate high protein (LCHP) diet, Zone diet and conventional weight loss diet on weight loss and body composition.
  2. Compare attrition rates of study participants based on assigned diet.
Inclusion Criteria:
  1. Obesity defined as BMI>27
  2. Age >18 and <55
  3. Considered in "generally good" health by PCP.
Exclusion Criteria:
  1. Hx of kidney or liver disease, including renal calculi and gout
  2. Pregnant or lactating
  3. Currently medicated for HTN, DM or hypercholesterolemia.
Description of Study Protocol:


  • Recruitment techniques were not specified. The only information provided was that participants gave informed consent and the study was approved by the Oklahoma University Health Sciences Center IRB.


  • Subjects were randomly assigned to one of three diet treatments for a 12-week treatment period. Randomization techniques were not specified. DEXA scans were used to measure body fat percentage, total body fat mass, total body lean mass and total body mass at the beginning and end of the study. Subjects returned to the clinic for weekly weigh-ins. Subjects on the LCHP diet also provided weekly urine samples to be checked for ketones.
  • The three diets are described as:
    1. Low Carbohydrate High Protein (LCHP) Diet: An RD calculated the minimum grams of high biological value protein to be consumed, based on each subject's lean body mass (from DEXA scan). Carbohydrate consumption to be <30 g per day. No calorie limit specified.
    2. Zone Diet: An RD calculated the amount of protein using the same method as the LCHP diet. Protein grams were broken into "blocks," as defined in Dr. Barry Sears' Zone Diet book. Participants were instructed to consume five meals or snacks per day, with fewer than five hours between feedings. Macronutrient distribution was 40% carbs, 30% protein and 30% fat.
    3. Conventional Diet: An RD calculated calorie needs based on the Harris-Benedict equation and the subject's ABW to promote weight loss of 0.45 kg per week.  Minimum calories was 1,200. Macronutrient distribution was 50% carbs, 20% protein and 30% fat. Diet plan was based on diabetic exchange system.


  • Subjects were instructed to continue their current physical activity level, to drink at least 64 ounces of non-caffeinated calorie-free fluid per day, take an MVI and record food intake in a provided diary.
  • Subjects on the LCHP diet received a carb counter booklet.
  • Those on the Zone diet received a copy of "A Week in the Zone" book, a handout with written instructions and a sample menu.
  • Those on the Conventional diet received a customized sample meal plan and a copy of "Exchange Lists for Meal Planning."

Statistical Analysis

  • One-way analysis (ANOVA) by diet and means comparison for all pairs using Tukey-Kramer honestly significant differences.
Data Collection Summary:

Timing of Measurements

  • DEXA scans recorded prior to and following the 12-week intervention. Baseline body weight was recorded at the beginning of the study and following each week of the 12-week intervention.

Dependent Variables

  • Body weight: Measured using a scale
  • Fat mass: Measured using DEXA scan
  • Lean mass: Measured using DEXA scan
  • Attrition Rate: Measured weekly, based on continued participation in study.

Independent Variables

  • Macronutrient distribution of diet broken into three treatment groups:
    1. LCHP diet
    2. Zone Diet
    3. Conventional diet.

Control Variables

  • None specified.
Description of Actual Data Sample:

Initial N

  • 91 subjects
  • Study did not specify gender breakdown for groups.

Attrition (final N)

  • 49 subjects
    • N=16 in LCHF group
    • N=12 in Zone group
    • N=21 in Conventional group
  • Study did not provide attrition reasons.


  • 18-55
  • Study did not provide mean age or age breakdown for each study group.


  • Not specified.

Other Relevant Demographics

  • Not specified.


  • BMI>27 was the only value provided
  • Study did not provide mean BMI for each study group.


  • Oklahoma
  • Study did not specify clinical setting or locations.
Summary of Results:


  • After the 12-week intervention, no significant differences were detected between the three study groups in total weight loss, body fat loss or lean tissue loss.



Zone Diet

Conventional Diet

Statistical Significance of Group Difference

Body Weight





Fat Mass





Lean Mass





Attrition Rate





Other Findings

  • Upon exit interview, no subjects following the LCHP diet expressed willingness to continue the diet. Zone participants who remained in the study "generally" liked the diet. Conventional dieters felt the diet closely followed a well-balanced eating plan that would promote healthy eating habits.
Author Conclusion:
The lack of significant findings may be secondary to the high rates of attrition and the small sample size. The study revealed that weight loss instruction must be kept simple, because peole have difficulties learning basic facts abouts carbohydrates, proteins and fat. Also, the diet plan that appealled to most participants is a conventional diet that closely approximates a "normal" healthful eating plan.
Funding Source:
University/Hospital: University of Oklahoma Health Science Center
Reviewer Comments:

There were several weaknesses with this study:

  • Participants were responsible for preparing all meals to meet diet specifications
  • Compliance was based on self-reported food logs
  • Age and activity level were not considered confounding variables
  • Recruitment and randomization schemes were not described.

While it is a good study concept, this study was not well implemented.

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? No
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? No
  2.4. Were the subjects/patients a representative sample of the relevant population? ???
3. Were study groups comparable? No
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) No
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? ???
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) No
  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? 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? ???
  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? No
  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)? No
  8.6. Was clinical significance as well as statistical significance reported? No
  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