AWM: Low Carbohydrate Diet (2006)
Stern L, Iqbal N, Seshadri P, Chicano KL, Daily DA, McGrory J, Williams M, Gracely EJ, Samaha FF. The effects of low-carbohydrate versus conventional weight loss diets in severely obese adults: one-year follow-up of a randomized trial. Ann Intern Med 2004; 140(10): 778-785.PubMed ID: 15148064
Recruited from Philadelphia VAMC.
Randomized Controlled Trial. Randomization performed using preestablished algorithm generated from random numbers.
Blinding used (if applicable)
Intervention (if applicable)
Assigned to either low-carbohydrate diet or low-fat, low-calorie diet
Primary end point was total weight loss at 1 year. Secondary analyses included change from baseline in serum lipid levels, insulin sensitivity, and glycemic control. 100 persons (50 per group) would be needed assuming a 2-sided type I error of 5% for the study to have 80% power to detect a 5 kg difference. Changes in weight, dietary intake, and metabolic data were compared by random-coefficient analysis. For all analyses, covariates included an indicator variable for time, diet group, and a diet group by time interaction term. Triglyceride, insulin and glucose levels were skewed and log-tranformed. Baseline differences between diet groups were compared by chi-square analyses for dichotomous variables and by the unpaired t test for continuous variables.
Timing of Measurements
Weight, self-reported medical history, and blood pressure collected at baseline, 6 months and 1 year.
- Weight measured through single calibrated scale
- Fasting blood specimens obtained for glucose, hemoglobin A1c, serum lipid levels
- LDL cholesterol calculated using Friedewald equation
- Presence of diabetes or metabolic syndrome
- Serum insulin through radioimmunoassay
- Insulin resistance in nondiabetic persons estimated by the quantitative insulin sensitivity check
- Low-carbohydrate diet (<30 g carbohydrate/day) or low-fat, low-calorie diet (-500 kcal/day, 30% kcals from fat). Diet groups met in weekly counseling sessions for 4 weeks, followed by 11 monthly sessions.
Initial N: 132 subjects, 64 in low-carbohydrate, 68 in low-fat
Attrition (final N): 79 subjects at 6 months, 87 subjects at 1 year (66% completion), 44 in low-carbohydrate, 18% female, 43 in low-fat, 19% female. 45 participants had missing data for diet recall and metabolic measurements.
Age: Low-carbohydrate diet: mean age 55 +/- 9 years, low-fat diet: 55 +/- 9 years
Ethnicity: Low-carbohydrate diet: 48% White, 48% African American, 5% Hispanic. Low-fat diet: 28% White, 70% African American, 2% Hispanic.
Other relevant demographics:
Anthropometrics: Participants well matched at baseline. Dropouts were not significantly different.
|Baseline||1 Year (n=87)||Change (n=87)||Mean Difference (95% CI)||P-value|
|Calories - low-fat||1919 +/- 940||1822 +/- 1008||-97 +/- 1067||-354 (-881 to 172)||0.183|
|Calories - low-carb||1972 +/- 1046||1462 +/- 776||-510 +/- 1187||
|Protein - low-fat||67 +/- 34 g||74 +/- 50 g||7 +/- 56 g||-15 (-39 to 9)||>0.2|
|Protein - low-carb||84 +/- 48 g||73 +/- 34 g||-11 +/- 56 g|
|Carbs - low-fat||252 +/- 139 g||230 +/- 150 g||-22 +/- 157 g||-98 (-179 to -40)||0.011|
|Carbs - low-carb||251 +/- 155 g||120 +/- 93 g||-131 +/- 168 g|
|Fat - low-fat||74 +/- 54 g||69 +/- 48 g||-6 +/- 55 g||28 (-14 to 70)||0.194|
|Fat - low-carb||72 +/- 50 g||93 +/- 117 g||
22 +/- 127 g
Caloric intake decreased more by 1 year in the low-carbohydrate group compared to the low-fat diet group, but the differences were not statistically significant.
By 1 year, mean weight change for persons on the low-carbohydrate diet was -5.1 +/- 8.7 kg compared with -3.1 +/- 8.4 kg for persons on the conventional diet. Differences between groups were not significant (-1.9 kg [95% CI: -4.9 to 1.0 kg], P = 0.20).
For persons on the low-carbohydrate diet, triglyceride levels decreased more (P = 0.044) and HDL cholesterol levels decreased less (P = 0.025).
As seen in the small group of persons with diabetes (n=54) and after adjustment for covariates, hemoglobin A1c levels improved more for persons on the low-carbohydrate diet.
These more favorable metabolic responses to a low-carbohydrate diet remained significant after adjustment for weight loss differences.
Changes in other lipids or insulin sensitivity did not differ between groups.
|Government:||Veteran Affairs Healthcare Network|
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?||???|
|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?||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?||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?||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?||???|
|8.1.||Were statistical analyses adequately described and the results reported appropriately?||???|
|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|