Adult Weight Management

AWM: Low Carbohydrate Diet (2006)

Citation:
Brehm BJ, Seeley RJ, Daniels SR, D'Alessio DA. A randomized trial comparing a very low carbohydrate diet and a calorie-restricted low fat diet on body weight and cardiovascular risk factors in healthy women. J Clin Endocrinol Metab 2003; 88: 1617-1623. PubMed ID: 12679447
 
Study Design:
Randomized Controlled Trial
Class:
A - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:
To determine the effects of a very low carbohydrate diet on body composition and cardiovascular risk factors.
Inclusion Criteria:
Age at least 18 years, moderate obesity (BMI 30 - 35) and stable weight over preceding 6 months (no weight loss or gain > 10% of their body weight).
Exclusion Criteria:
Presence of cardiovascular disease, untreated hypertension, diabetes, hypothyroidism, substance abuse, pregnancy or lactation.
Description of Study Protocol:

Recruitment

Recruited by advertisement.

Design

Randomized controlled trial.

Blinding used (if applicable)

DEXA and biochemical analyses were made by blinded personnel.

Intervention (if applicable)

Subjects randomized to 6 months of ad libitum very low carbohydrate diet or calorie-restricted diet with 30% calories as fat.  Randomized using random number table.

Statistical Analysis

Prior estimate that 20 - 25 subjects per group would be needed to demonstrate a 25% difference in weight loss and a 30% difference in LDL cholesterol between the regimens.  Baseline characteristics compared between 2 groups using t tests.  To assess effects of diets, 2-way repeated measures ANOVA, with time as the repeated factor, was performed.  If main effect was significant, Bonferroni multiple comparison was implemented to determine significant differences.  Differences between groups are indicated only when there is a significant interaction between diet and time.  Body weight, biochemical parameters and DEXA measurements analyzed for the completers.  Body weight also analyzed for entire randomized cohort.  In this intention to treat analysis, initial weights for subjects who withdrew were used as follow-up weights at 3 and 6 months.

Data Collection Summary:

Timing of Measurements

Anthropometric and metabolic measures assessed at baseline, 3 months and 6 months.

Dependent Variables

  • Height
  • Weight on a single electronic scale
  • Blood pressure measurements made by auscultation using an appropriate sized cuff with subject seated quietly
  • Fasting blood samples analyzed for total, HDL and LDL cholesterol, glucose, insulin, leptin, beta-hydroxybutyrate, and triglycerides
  • ECG
  • Body fat measured by DEXA
  • Assessment of urinary ketones performed with Ketostix

Independent Variables

  • 6 months of ad libitum very low carbohydrate diet (maximum intake of carbohydrate of 20 g for 2 weeks, then allowed increase to 40 - 60 g) or calorie-restricted low fat diet (55% kcals from carbohydrate, 15% protein, 30% fat).  Calorie prescriptions based on body size and Harris-Benedict equation.  For 3 months, subjects attended group meetings held biweekly, on alternating weeks subjects met for individualized counseling with RD to review 3-day food records from previous week.  Subjects advised to continue baseline level of activity.  After 3 months, no scheduled RD contact.

Control Variables

 

Description of Actual Data Sample:

Initial N: 226 screened for eligibility.  53 females randomized.

Attrition (final N):  42 (79%) completed the trial.  4 dropouts from very-low-carbohydrate group (n=22), 7 from low fat diet group (n=20).

Age: Low-fat diet group mean:  43.10 +/- 8.56 years, very low carbohydrate group mean:  44.22 +/- 6.84 years

Ethnicity:  13 African Americans and 40 Caucasians at baseline 

Other relevant demographics:  Low-fat diet group mean BMI:  34.04 +/- 1.83, very-low-carbohydrate group mean BMI: 33.17 +/- 1.83 

Anthropometrics:  There were no significant differences between groups at baseline.

Location:  Ohio 

 

Summary of Results:

 

Baseline 3 Months 6 Months
Low Carb - energy 1608 kcal 1156

1302

Low Carb - % protein

16

28

23

Low Carb - % CHO 47 15 30
Low Carb - % fat 37 57 46
Low Fat - energy 1707 kcal 1245 1247
Low Fat - % protein 15 18 18
Low Fat - % CHO 47 54 53
Low Fat - % fat

38

28

29

Other Findings

Women on both diets reduced calorie consumption by comparable amounts at 3 and 6 months.

The very low carbohydrate diet group lost more weight (8.5 +/- 1.0 vs 3.9 +/- 1.0 kg, P < 0.001) and more body fat (4.8 +/- 0.67 vs 2.0 +/- 0.75 kg, P < 0.01) than the low fat diet group.

Mean levels of blood pressure, lipids, fasting glucose, and insulin were within normal ranges in both groups at baseline.  Although all of these parameters improved over the course of the study, there were no differences observed between diet groups at 3 or 6 months.

Beta-hydroxybutyrate increased significantly in the very low carbohydrate group at 3 months (P = 0.001).

Author Conclusion:
Based on these data, a very low carbohydrate diet is more effective than a low fat diet for short-term weight loss and over 6 months, is not associated with deleterious effects on important cardiovascular risk factors in healthy women.
Funding Source:
Government: NIH
University/Hospital: University of Cincinnati Research Council, Children Hospital Medical Center
Not-for-profit
0
Foundation associated with industry:
Reviewer Comments:
Dietary compliance assessed biweekly with RD.
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? 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? 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