DLM: Diet Composition (2010)
- To determine whether the replacement of dietary saturated fat with monounsaturated fat, as opposed to carbohydrate, would result in a better overall risk factor profile in non-diabetic individuals with one or more of the following: Low HDL-cholesterol, high triacylglycerol, or high insulin concentrations
- To evaluate two separate post-prandial conditions
- To explore whether the diet response would differ depending on baseline lipid concentrations or the presence of the metabolic syndrome and insulin resistance.
- Aged 21-65 years
- Likely at risk of the potential negative effects of low-fat diets; meaning the average of two screening measurements met the following: HDL ≤30th percentile, triacylglycerol ≥70th percentile and insulin ≥70th percentile
- In good health, free of chronic disease and taking no medications known to affect lipids or thrombotic factors.
- Average screening total cholesterol <25th percentile or >90th percentile
- LDL >4.91mmol/L
- Fasting triacylglycerol <30th percentile or >5.65mmol/L
- HDL >70th percentile.
Recruitment
Recruitment methods not described.
Design
- Randomized crossover trial
- Three diets fed in a double-blind, three-way crossover with each diet lasting seven weeks with a rest period of four to six weeks between each diet
- All food was provided except for a self-selected meal on Saturday evenings
- The meal was to follow the NCEP Adult Treatment Panel (ATP) Step I guidelines.
Blinding Used
Double-blind.
Intervention
- Average American diet (AAD) to reflect the typical pattern of US population
- Carbohydrate-replacement diet (CHO diet) to meet the nutrient specifications of the NCEP Step I diet. It contained more fiber than the AAD.
- Monounsaturated fat-replacement diet (MUFA diet) to match the saturated fat (SFA) and polyunsaturated fat content of the CHO diet but also the total fat of the AAD
- Seven percent of energy from SFAs was replaced with either CHO (primarily complex) on the CHO diet or with MUFAs on the MUFA diet
- All three diets provided 300mg cholesterol per day.
Statistical Analysis
- The linear statistical model, the set of primary hypotheses, the strategy for controlling type I error and the estimation procedures were all specified a priori
- P<0.01 as chosen as statistically significant.
Timing of Measurements
- Blood samples at weeks five, six and seven of each of the three diets
- Weights twice weekly
- Two day-long studies during week seven of each diet to study the effect of eating natural food and a high-fat load.
Dependent Variables
- Total cholesterol, LDL, HDL, triacylglycerol, glucose, uric acid (enzymatic assay)
- Apolipoprotein (apo) A-1 and apo B (rate immunonephelometry)
- Lipoprotein(a) [Lp(a)] (enzyme-linked immunosorbent assay)
- Insulin (radioimmunoassay)
- Insulin resistance (homeostasis model assessment of insulin resistance (HOMA-IR) index).
Independent Variables
- Average American diet (16% protein, 47% CHO, 37% fat [16% SFA, 14% MUFA, 7% PUFA]),7.5g fiber, 300mg cholesterol
- CHO diet (16% protein, 54% CHO, 30% fat [8%SFA, 15% MUFA, 7% PUFA]),15g fiber, 300mg cholesterol
- MUFA diets (16% protein, 47% CHO, 37% fat [8%SFA, 22% MUFA, 7% PUFA]),7.5g fiber, 300mg cholesterol
- High fat load meal: 105g fat (52g SFA), 48g CHO, 32g protein, 300mg cholesterol and 1,237calories per 2m2 body surface area.
Control Variables
None.
- Initial N: 110
- Attrition (final N): 85 for all three diets (33 females)
- Age: 35.5±9.4 (range 21-61 years)
- Ethnicity: 10 African Americans
- Other relevant demographics: Not applicable
- Anthropometrics: Not applicable
- Location: New York, Louisiana, Pennsylvania, Minnesota.
Key Findings
- Relative to the average American diet, LDL-cholesterol was lower with both the CHO (-7.0%) and MUFA (-6.3%) diets, whereas the difference in HDL-cholesterol was smaller during the MUFA diet (-4.3%) than during the CHO diet (-7.2%)
- Plasma triacylglycerols tended to be lower with the MUFA diet, but were significantly higher with the CHO diet
- Post-prandial triacylglycerol concentrations did not differ significantly between the diets
- Lipoprotein (a) concentrations increased with both the CHO (20%) and MUFA (11%) diets relative to the average American diet.
Table: Effect of Diet on Primary End-points
Variables | AAD | MUFA diet | CHO diet |
Total cholesterol (mmol/L) | 5.17±0.08 |
4.86±0.082 |
4.89±0.082 |
LDL cholesterol (mmol/L) |
3.31±0.08 |
3.10±0.082 |
3.08±0.082 |
HDL cholesterol (mmol/L) |
1.08±0.03 |
1.03±0.032 |
1.00±0.022,3 |
Triacylglycerols (mmol/L) | 1.48±0.038 |
1.42±0.07 |
1.59±0.082,3 |
Apolipoprotein A-1 (mg/dL) | 128±2 | 125±22 | 122±22 |
Apolipoprotein B-1 (mg/dL) | 110±3 | 106±22 | 107±22 |
Lipoprotein (a) (mg/dL) | 9.9±1.4 | 11.0±1.52 | 11.9±1.62 |
Glucose (mmol/L) | 5.1±0.1 | 5.1±0.1 | 5.1±0.1 |
Insulin (µU/mL) | 12.2±0.6 | 12.3±0.6 | 12.1±0.7 |
All values are mean ± SEM, except for triacylglycerols and Lp(a), which are medians ± SEM.
2Significantly different from AAD on the basis of adjusted values from the a priori linear regression model, P<0.01.
3Significantly different from MUFA diet on the basis of adjusted values from the a priori linear regression model, P<0.01.
Other Findings
- Triacylglycerol concentrations with the AAD diet were significantly higher in subjects with metabolic syndrome (N=20; 12 men and eight women) or with insulin resistance (N=28; 18 men and 10 women) than in subjects who did not fulfill these criteria
- Glucose concentrations were lower in the post-lunch phase of the day-long study for the CHO diet. Insulin concentrations were highest with the AAD diet during the day-long study.
- In individuals considered at increased risk of CAD, the replacement of dietary SFA with MUFA rather than CHO is preferred because of associated smaller reduction in HDL cholesterol and a trend toward a reduction in fasting triacylglycerol concentrations
- Dietary recommendations based on underlying risk factors may be a more effective approach for CAD prevention.
Government: | NIH |
In-Kind support reported by Industry: | Yes |
All foods provided. Authors note the following limitations:
Subjects' weights were maintained, so the issue of dietary effects on lipid concentrations under free-living conditions is unknown.
Quality Criteria Checklist: Primary Research
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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? | N/A | |
6.6. | Were extra or unplanned treatments described? | N/A | |
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)? | N/A | |
8.5. | Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? | N/A | |
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 | |