Adult Weight Management

AWM: Low Carbohydrate Diet (2006)

Study Design:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
What effect does a low carbohydrate, high protein, high fat Atkins diet have on weight loss and coronary heart disease risk factors?
Inclusion Criteria:

Healthy men and women who both:

  1. Signed a consent form approved by participating institutional IRBs
  2. Were screened for appropriateness by completing a comprehensive medical exam and routine blood test.
Exclusion Criteria:

Any clinically significant illness including:

  • Type 2 Diabetes Mellitus
  • Taking lipid-lowering medications
  • Medications that affected body weight
  • Pregnant or lactating.
Description of Study Protocol:


  • Does not specify.


  • Random-number generator assigned each subject randomly at each of four sites.
  • Clincal Trial with one of two diets:
    1. Low CHO, high PRO, high fat
    2. High CHO, low fat
  • Randomly assigned as treatment for 12 months.

Blinding used (if applicable)

  • None.

Intervention (if applicable)

  • Subjects met with an RD for 15 to 30 minutes at three, six and 12 months
  • Specific books and manuals were provided to each subject addressing assigned diet protocol.

Statistical Analysis

  • ANOVA determined no effects of research site on weight loss or attrition at three, six or 12 months, so all subjects were analyzed together.
  • T-test independent samples differeneces between two groups at baseline
  • Primary analyses: Repeated measures ANOVA
  • Secondary analyses: Covariance ANOVA
  • Chi-square analyses to determine differences between groups in categorical variables. Correlations were further analyzed with Spearman's RHO coefficient.
  • SPSS v/11 software used.
Data Collection Summary:

Timing of Measurements

  • Weight, blood pressure, urinary ketones assessed at baseline, two, four, eight,  12, 16, 20, 26, 34, 42 and 52 weeks
  • Fasting blood samples and an oral glucose tolerance test were taken at baseline, three, six and 12 months.

Dependent Variables

  • Variable One: Weight; light clothing, no shoes, calibrated scales
  • Variable Two: Blood pressure
  • Variable Three: Urinary ketones; Ketostix read either positive or negative
  • Variable Four: OGGT
  • Variable Five: Fasting blood samples
    • Serum total CHO, HDL, TG using CDC assay protocol
    • Plasma insulin; radioimmunoassay
    • Plasma glucose; glucose oxidase autoanalyzer.

Independent Variables

  • Group One: Low CHO, high PRO, high fat diet
  • Group Two: Conventional diet (high CHO, low fat, low kcal
    • Women: 1,200-1,500 kcal
    • Men: 1,500-1,800 kcal.

Control Variables

  • None specified.
Description of Actual Data Sample:

Initial N

  • 63: 43 female, 20 male.

Attrition (final N)

  • 49 completed three months
  • 42 completed six months
  • 37 subjects completed 12 months
  • 59% subjects completed the study.


  • Mean age: 44.0±9.4
  • Low CHO: 44.2±7.0 (unconventional diet).


  • Low CHO diet
    • White: 26
    • Black: Four
    • Hispanic: Three.
  • Conventional diet
    • White: 22
    • Black: Eight
    • Hipanic: None.

Other Relevant Demographics

  • BMI
    • Low CHO diet: 33.93±3.8
    • Conventional diet: 34.4±3.1.
  • Weight
    • Low CHO diet: 98.7±19.5 kg
    • Conventional diet: 98.3±16.4 kg.


  • No specific sites provided.
Summary of Results:


Treatment Group

Measures and Confidence Intervals

Control group

Measures and Confidence Intervals

Statistical Significance of Group Difference

Study attrition


Low CHO: 39% attrition, 12 months

4% > weight loss up to six nth



High CHO: 43% attrition, 12 months




No significance

P=0.002 at three months

P=0.03 at six months

No significance (P=0.27)at 12 months

Insulin sensitivity




Positive: Up to three months


At six months (P=0.94) Positive up to six months

P<0.05 difference from baseline



Diastolic BP




P<0.05 (P=0.84) three months

Author Conclusion:
  • Self-help format increased attrition. The mechanism for decreased energy intake in subjects following the low DHO diet was unknown (possibly the monotony of the diet or the diet interacted with appetite or satiety) but ketosis unlikely, since no correlation was found between ketosis and weight loss.
  • Limitations: Small sample size. One year longer may have been more precise with better measure of insulin sensitivity.
  • No additional intervention, if necessary, was reported for study participants.
Funding Source:
Government: NIH
University/Hospital: Unviersity of Pensylvania School of Medicine, University of Colorado Health Sciences Center, Washington Unviersity School of Medicine, Thomas Jefferson University
Reviewer Comments:


  • Excellent: Would like to see a study in which fat is controlled to determine which macronutrients (CHO or PRO) have more effect on CAD markers.


  • These data do not demonstrate an effect of macronutrient composition, independent of weight loss, on insulin sensitivity in obese subjects without diabetes. However, the results of these metabolic studies should be interpreted with caution, given the study’s relatively small sample size and the one-year duration. Additional studies in which more precise measures of insulin sensitivity are used are needed to evaluate this issue more carefully.
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? ???
  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? ???
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? No
  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.) ???
  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? ???
  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? No
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? No
  6.6. Were extra or unplanned treatments described? No
  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? 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)? 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? ???
  8.7. If negative findings, was a power calculation reported to address type 2 error? ???
9. Are conclusions supported by results with biases and limitations taken into consideration? N/A
  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