AWM: Low Carbohydrate Diet (2006)
Yancy WS, Olsen MK, Guyton JR, Bakst RP, Westman EC. A low-carbohydrate, ketogenic diet vs. a low-fat diet to treat obesity and hyperlipidemia: a randomized controlled trial. Ann Intern Med, 2004; 140: 769-777.PubMed ID: 15148063
- 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.
- 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.
- Recruited from the community, method not defined.
- 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.
- 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.
Timing of Measurements
- Group visits twice a month for three months, then monthly for three months.
- 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.
- 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.
- 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.
- Low-fat: 44.1±8.7
- Low-carbohydrate: 45.3±9.5.
- 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.
- Groups were similar, statistics not reported.
- North Carolina, USA.
- 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.
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.
|University/Hospital:||Robert C. Atkins Foundation|
Quality Criteria Checklist: Primary Research
|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|
|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|