AWM: Low Carbohydrate Diet (2006)
Citation:
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
To examine body weight, body composition, serum lipid levels and adverse effects over 24 weeks in hyperlipidemic persons, who were randomly assigned to follow a low-carbohydrate ketogenic diet or a low-fat, low-cholesterol, reduced-calorie diet commonly used to induce weight loss and decrease serum lipid levels.
Inclusion Criteria:
- Aged 18 to 65 years
- BMI 30 to 60
- Desire to lose weight
- Elevated lipid levels [total cholesterol >5.17 mmol/L (>200 mg/dl)]
- LDL cholesterol level >3.36 mmol/L (>130 mg/dl)
- Triglyceride level >2.26 mmol/L (>200 mg/dl)
- No serious medical condition.
Exclusion Criteria:
- Use of any prescription medication in the previous two months (except for oral contraceptives, estrogen therapy and stable thyroid medication)
- Pregnancy or breastfeeding
- Use of any weight loss diet or diet pills in the previous six months
- Baseline ketonuria.
Description of Study Protocol:
Recruitment
- Recruited from the community, method not defined.
Design
- Randomized controlled trial, randomized using computer-generated simple randomization list.
Blinding used (if applicable)
- Not used.
Intervention (if applicable)
- Low-carbohydrate diet (<20g carbohydrates per day) plus nutritional supplementation, exercise recommendations and group meetings or low-fat diet (<30% energy from fat, <300mg cholesterol daily and deficit of 500-1,000kcals per day) plus exercise recommendations and group meetings, for 24 weeks.
Statistical Analysis
- For categorical outcomes, groups were compared using chi-square test or Fisher exact test, as appropriate. For all primary and secondary continuous outcomes, linear mixed-effects models that included fixed and random effects were used to determine expected mean values at each time point and to test hypotheses of group differences.
- In most body weight and body composition models, time and group assignments were included as fixed effects with linear and quadratic time-by-group interaction terms.
- In the fat-free mass, total body water and vital sign models, time-by-group interaction was treated as a categorical variable.
- In all body weight and body composition models, random effects included intercept and linear slope terms. For the serum outcome measure models, the time-by-group interaction was treated as a categorical variable and an unstructured covariance was used to account for within-patient correlation over time.
- All available data, including those from participants who subsequently discontinued the study, were used for the longitudinal analyses. Mixed-effects models assume non-informative dropout, meaning that the probability of dropout may depend on covariates or participants' previous responses, but not on current or future responses.
Data Collection Summary:
Timing of Measurements
- Group visits twice a month for three months, then monthly for three months.
Dependent Variables
- Body weight on same calibrated scale while wearing lightweight clothing and no shoes
- Body composition through biolectrical impedance
- Blood pressure and pulse rate measured in non-dominant arm by automated digital cuff
- Fasting blood samples analyzed for serum lipid levels and other metabolic parameters
- Tolerability and adverse effects measured through questionnaire
- Urinalysis for ketonuria through dipstick.
Independent Variables
- Low-carbohydrate diet (<20g carbohydrates per day) and nutritional supplements or low-fat diet (<30% kcals from fat, <10% saturated fat, <300mg cholesterol, 500-1,000 kcal restriction based on body weight in lbs x10).
- Both groups received group meetings, diet instruction and exercise recommendations.
- One-hour group meetings took place twice monthly for three months, then monthly for two months.
- Participants selected own menus and prepared or bought own meals.
- Dietary adherence measured by self-report, food records and urinary ketones for low-carbohydrate group. Diet composition analyzed for subsample of 20 people, 13 from low-carbohydrate, seven from low-fat.
- Encouraged to exercise for 30 minutes three times per week.
Description of Actual Data Sample:
Initial N
- 1,051 volunteers screened for eligibility.
- 120 underwent randomization.
Attrition (final N)
- 79 of 120 subjects completed the study (34% dropout rate)
- 45 of 59 (76%) low-carbohydrate subjects
- 34 of 60 (57%) low-fat subjects.
Age
- Low-fat: 44.1±8.7
- Low-carbohydrate: 45.3±9.5.
Ethnicity
- Low fat: 79% white, 18% African-American
- Low-carbohydrate: 80% white, 18% African-American.
Other Relevant Demographics
- Low fat BMI: 33.9±5.3
- Low-carbohydrate BMI: 34.6±5.2.
Anthropometrics
- Groups were similar, statistics not reported.
Location
- North Carolina, USA.
Summary of Results:
Other Findings
- A greater proportion of the low-carbohydrate diet group than the low-fat diet group completed the study (76% vs. 57%, P=0.02).
- 13 low-carbohydrate subjects consumed 8% kcals from carbohydrates, 26% from protein and 68% from fat. Seven low-fat subjects consumed 52% of kcals from carbohydrates, 19% from protein and 29% from fat. Estimated daily energy intake was 6.14±1.37 MJ (1,461.0±325.7kcal) in the low-carbohydrate group and 6.31±0.68 MJ (1,502.0±162.1kcal) in the low-fat group.
- At 24 weeks, weight loss was greater in the low-carbohydrate diet group than in the low-fat diet group (mean change: -12.9% vs. -6.7%, P<0.001).
- Patients in both groups lost substantially more fat mass (change: -9.4kg with low-carbohydrate vs. -4.8kg with low-fat diet) than fat-free mass (change: -3.3kg vs. -2.4kg, respectively; P=0.054).
- Compared with recipients of the low-fat diet, recipients of the low-carbohydrate diet had greater decreases in serum triglyceride levels [change: -0.84mmol/L vs. -0.31mmol/L (-74.2mg/dl vs. -27.9mg/dl); P=0.004] and greater increases in HDL cholesterol levels [0.14mmol/L vs. -0.04mmol/L (5.5mg/dl vs. -1.6mg/dl); P<0.001].
- Changes in LDL cholesterol level did not differ statistically [0.04mmol/L (1.6mg/dl) with the low-carbohydrate diet and -0.19mmol/L (-7.4mg/dl) with the low-fat diet; P=0.2].
- Minor adverse effects were more frequent in the low-carbohydrate diet group.
Author Conclusion:
In summary, over 24 weeks, healthy hyperlipidemic persons who followed a low-carbohydrate diet lost more body weight and body fat than did those who followed a low-fat diet. Serum lipid profiles improved in both groups, but monitoring remains important because a small percentage of persons may experience adverse changes. Further research is needed in other groups and for longer periods to determine the safety of this dietary approach.
Funding Source:
University/Hospital: | Robert C. Atkins Foundation |
Reviewer Comments:
Large dropout rates, especially in low-fat group. Diet composition only reported for 20 subjects: 13 in the low-carbohydrate group, seven in low-fat.
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? | ??? | |
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? | ??? | |
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? | ??? | |
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%.) | ??? | |
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? | ??? | |
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? | 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? | ??? | |
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? | ??? | |
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)? | N/A | |
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 | |