Adult Weight Management

AWM: Low Carbohydrate Diet (2006)


Meckling KA, O'Sullivan C, Saari D. Comparison of a low-fat diet to a low-carbohydrate diet on weight loss, body composition, and risk factors for diabetes and cardiovascular disease in free-living, overweight men and women. J Clin Endocrinol Metab. 2004; 89(6): 2717-2723.

PubMed ID: 15181047
Study Design:
Randomized controlled trial
A - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:
To compare the effects of a conventional energy-restricted low-fat diet with an equivalent energy-restricted low-carbohydrate diet on weight loss.
Inclusion Criteria:

BMI>25 with the potential for weight loss of nine kg or more without becoming underweight (BMI<20), sufficient energy intake as based on habitual diet (>4,000 kJ per day) and strong personal motivation.

Exclusion Criteria:
Patients were ineligible if they were on medications known to affect blood glucose, blood lipids or blood pressure. Individuals with obesity secondary to clinically diagnosed endocrine disease were also excluded.
Description of Study Protocol:


  • Via poster and newspaper advertisements.


  • Randomized controlled trial.

Blinding used

  • Data concerning certain parameters not unblinded to identify subjects until after all samples had been analyzed.


  • Assigned to low-fat or low-carbohydrate diet for 10 weeks.

Statistical Analysis

  • Not described.
Data Collection Summary:

Timing of Measurements

  • Subjects met weekly with diet coordinator for weight measurements and consultation.

Dependent Variables

  • Weight measured in similar clothing without shoes, using electronic scale
  • Blood pressure measured while subject was seated in a chair after a five-minute rest period, using digital self-inflating cuff
  • Body composition measured by BIA
  • Fasting venous blood samples analyzed for total, LDL and HDL cholesterol, triglycerides, beta-hydroxybutyrate, insulin, plasminogen activator inhibitor-1 and glucose.

Independent Variables

  • Participants recorded at least seven days of diet records before commencing the study.
  • Assigned to low-fat or low-carbohydrate (goal: 50 to 70 g carbohydrates per day) diets. 
  • Subjects given food and exercise journals to maintain for study.
  • Instructed not to modify activity and exercise programs.
  • Restriction in carbohydrates resulted in energy restriction of 5,020 to 6,690 kJ per day in females, 5,860 to 9,200 kJ per day in males, subjects on low-fat diet energy-restricted to achieve same restriction as those on low-carbohydrate diet.
Description of Actual Data Sample:

  • Initial N: 40 subjects
    • 10 males
    • 30 females
    • 20 in each experimental group.
  • Attrition (final N): 31 completed the study (23% dropout rate).
    • Four dropped out of low-fat
    • Five dropped out of low-carbohydrate.
  • Age
    • Low-fat: Mean age 43.2 years
    • Low-carbohydrate: Mean age 41.2 years.
  • Ethnicity: Not mentioned.
  • Other relevant demographics
    • Low-fat BMI: 32.2±0.9
    • Low-carbohydrate BMI: 32.2±1.5 at baseline
  • Anthropometrics: Groups were comparable in terms of sex distribution, age, weight, height and BMI.
  • Location: Guelph, Canada.
Summary of Results:

LF baseline LF 10 weeks LC baseline LC 10 weeks
Energy (kJ) 8,617±414 6.077±255 9,616±600 6,421±353
Protein (g) 82.4±4.0




Protein (percentage) 16.0±0.8 19.5±1.1 15.4±1.3 26.2±1.4
Fat (g) 80.9±4.9 28.8±2.6 90.8±7.9 94.6±3.9
Fat (percentage) 36.4±2.2 17.8±1.6 35.6±2.7 55.5±3.9
Carbs (g) 251±13 225±9 287±26 59±3
Carbs (percentage) 49.0±2.7




Other Findings

  • Subjects on the low-fat diet consumed an average of 17.8% of energy from fat, compared with their habitual intake of 36.4%, resulting in an energy restriction of 2,540 kJ per day.
  • Subjects on the low-carbohydrate diet consumed an average of 15.4% of energy from carbohydrates, compared with habitual intakes of 50%, resulting in an energy restriction of 3,195 kJ per day.
  • Both groups of subjects had significant weight loss over the 10 weeks and nearly identical improvements in body weight and fat mass. There was no difference between diets in terms of level of energy restriction.
  • Low-fat subjects lost an average of 6.8 kg and had a decrease in BMI of 2.2, compared with a loss of 7.0 kg and a BMI decrease of 2.1 in the low-carbohydrate subjects. There was no difference in the pattern of weight loss between groups.
  • The low-fat group better preserved lean body mass, when compared with the low-carbohydrate group. However, only the low-carbohydrate group had a significant decrease in circulating insulin concentrations.
  • Group results indicated that the diets were equally effective in reducing systolic blood pressure by about 10 mm Hg and diastolic blood pressure by five mm Hg and decreasing plasminogen activator inhibitor-1 bioactivity.
  • Blood beta-hydroxybutyrate concentrations were increased in the low-carbohydrate group only, at the two- and four-week time points.
Author Conclusion:

In conclusion, hypoenergetic diets of widely differing macronutrient concentration are feasible strategies for promoting short-term weight loss and improvements in chronic disease risk markers in overweight and obese men and women.

A low-fat regimen may be preferred when reduction of blood cholesterol is a primary goal, whereas the low carbohydrate regimen may be more appropriate when improvement in insulin sensitivity is the target. Either strategy promotes loss of fat weight and improvements of similar magnitude in blood pressure and triglycerides, both of which can be seen as additional benefits to chronic disease risk reduction in addition to weight loss itself.

Funding Source:
Government: natural sciences engineering research council
Reviewer Comments:

Statistical analysis not described.

Low-carbohydrate energy restriction seemed to be the driver for the low-fat energy restriction.

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? 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? Yes
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? Yes
  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.) Yes
  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? ???
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? ???
  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? ???
  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? ???
  8.1. Were statistical analyses adequately described and the results reported appropriately? No
  8.2. Were correct statistical tests used and assumptions of test not violated? ???
  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)? ???
  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? ???
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