DLM: Almonds (2009)

Citation:
 
Study Design:
Class:
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Quality Rating:
Research Purpose:

To assess the effects of whole unblanched almonds at two doses on the blood lipids of hyperlipidemic subjects, when provided as supplements to their self-selected therapeutic diets.

Inclusion Criteria:

Hyperlipidemia with LDL-cholesterol exceeding 4.1mmol per L and triglycerides under 4.0mmol per L. 

Exclusion Criteria:

No subjects exhibited signs of diabetes, liver or renal disease.

Description of Study Protocol:
  • Recruitment: By newspaper ad and from patients attending the Risk Factor Modification Center, St. Michael's Hospital
  • Design: Randomized crossover. 

Intervention

  • The National Cholesterol Education Program Step II Diet (saturated fat under 7% of energy and dietary cholesterol under 200mg per day) was followed by all subjects
  • For subjects new to the diet, instruction was given at least one month prior to initiation of the study and at Weeks One and Two of each phase
  • Three supplements were: Whole raw unblanched almonds (73±3g per day), muffins (147±6g per day) and half portions of almonds with half portion of muffins
  • All subjects took all three supplements, crossing over each month: The level of supplement was based on their estimated daily energy requirement, providing 22.2% of energy needs and the supplements were isoenergetic (mean, 423kcal per day)
  • Fasting serum (total cholesterol, tryglyceride, HDL, apolipoprotein A-1 and B, lipoprotein (a), C-reactive protein and L-homocysteine), blood pressure and body weight measurements were obtained at Weeks Zero, Two and Four of each phase
  • Expired air was evaluated for nitrous oxide at Weeks Zero and Four of each phase
  • Compliance was assessed from seven-day diet records and a supplement record
  • All foods and supplements were weighed during this assessment.

Statistical Analysis

  • The results are expressed as means ±SEM
  • The mean of Weeks Two and Four for each phase was used in calculating treatment differences
  • The significance of the percentage difference between treatments was assessed by two-tailed Student's T-test for paired data
  • The absolute difference between treatments was assessed by the method of least squares means within the mixed model procedure (PROC MIXED/SAS), with a Tukey adjustment for multiple means comparisons. The model included the main effects of diet, sex X sequence interaction and a random term representing the subject nested within the sex X sequence interaction and the baseline value as a covariate.
  • To test for the overall effect of diet-sex interaction, ANCOVA (PROC GLM/SAS) was used with the same model specification
  • Student's T-test for paired data (two-tailed) was used to assess the significance of percentage changes across diets
  • The Framingham predictive equation for cardiovascular disease risk was also applied to the data by using the total: HDL-cholesterol and systolic blood pressure results (SAS/STAT version 8, 1997; SAS Institute).
Data Collection Summary:

Timing of Measurements

  • Serum: Baseline and Weeks Two and Four of each phase
  • Expired air: Weeks Zero and Four of each phase.

Dependent Variables

  • Blood samples were drawn after an overnight fast of 12 hours and stored at -70o C
    • Serum samples were analyzed for total cholesterol, triacylglycerols and HDL-cholesterol in a single batch after dextran sulfate-magnesium chloride precipitation
    • LDL-cholesterol was calculated by the Friedewald equation
    • Serum apolipoprotein A-1 and B were measured by nephelometry
    • Lipoprotein(a) was analyzed by a commercial ELISA kit
    • C-reactive protein was analyzed by end-point nephelometry
    • Plasma homocysteine was analyzed by fluorescence polarization immunoassay.
  • Exhaled nitrous oxide was collected by an offline method with fixed-flow expired air
  • Blood pressure was measured with the subjects seated.

Independent Variables

  • Seven-day food records were collected during the last seven days of each phase
  • The subjects weighed their food on self-taring electronic scales
  • Macronutrients were analyzed using a database derived from food-composition tables of the US Department of Agriculture and from food labels
  • The supplements used in the study were analyzed with use of Association of Official Analytical Chemists' methods for fat, protein and fiber, with available carbohydrates determined by difference
  • The fatty acid composition was determined by gas chromatography.
Description of Actual Data Sample:
  • Initial N: 43 (gender not described)
  • Attrition (final N): 27 (15 men and 12 post-menopausal women)
  • Age: 64±9 years (range, 48 to 86 years)
  • Ethnicity: Not described

Anthropometrics

  • BMI was 25.7±3.0 (range, 20.5kg to 31.5 kg per m2)
  • Location: Toronto, Canada.
Summary of Results:

Relative Risks (95% CI) of CHD, According to Quintiles of Updated Linolenic Fatty Acid Intake
Percentage reduction, compared with baseline values

Variable (Percentage Change)
Half-Dose Almonds P< Full-Dose Almonds P<
Total Cholesterol
3.1±1.5 0.043 5.6±1.4 0.001
LDL Cholesterol 4.4±1.7 0.018 9.4±1.9 0.001
Apo B 3.0±1.5 0.057 7.3±1.6 0.001
Total:HDL Cholesterol
6.6±2.1 0.004 8.4±1.7 0.001
LDL:HDL Cholesterol 7.8±2.2 0.001 12.0±2.1 0.001
ApoB:A-1
4.3±1.6 0.01 8.2±1.7 0.001
Lp(a)
  NS 7.8±3.5 0.034

  • HDL was increased 4.6±2.0% (P=0.034) on the half-dose almonds and 3.8±1.8% (P=0.047) on the full-dose almonds
  • On the muffin control diet, the only significant change from baseline was the increase in triglycerides (10.8±4.7%; P=0.031).

In comparison to the control values, values for full-dose almonds confirmed the significantly lower blood concentrations for:

  • Total cholesterol: P=0.006
  • LDL cholesterol: P=0.002
  • ApoB: P=0.002
  • Total:HDL cholesterol: P<0.001
  • LDL:HDL cholesterol: P<0.001
  • ApoB:A-1: P<0.001
  • Lp(a): P=0.026.

HDL cholesterol values were higher on full-dose almonds, compared to control (P=0.041). 

Other Findings

Subjects ate 98.1±0.8% of the control muffin diet, 99.5±0.6% of the half-dose muffin plus half-dose almonds and 97.8±0.7% of the full-dose almonds. The full-dose almonds were perceived more palatable than the control muffin, on a scale of one to 10 (control, 6.5±0.4; almond, 8.4±0.3; P<0.001). There was no significant change in body weight with either diet. 

There was no significant difference between the genders in response to diet. Age and body mass index did not influence the treatment effect. The two subjects who were taking an antihyperlipidemic agent had similar response. Controlling for weight change or difference in dietary carbohydrate, saturated or polyunsaturated fat, the ratio of polyunsaturated to saturated fatty acids or dietary cholesterol in the general linear model procedure did not alter the pattern of significance in treatment differences of blood lipids. 

No significant differences were seen in homocysteine, C-reactive protein, blood pressure or pulmonary NO. No significant differences were seen between Week Two and four blood lipid values.

Calculated CHD risk for the full dose of almonds was significantly reduced, compared with baseline (9.2±3.5%, P=0.015) and compared with the control value (P=0.029).

Author Conclusion:
  • Almonds, substituted for whole wheat flour muffins of similar calorie and SFA, PUFA and protein content, reduced lipid risk factors for CHD, even in diets already low in saturated fat
  • The macronutrient content of the control muffins likely reduced the contrast that would have been seen if the subjects used commercial muffins
  • Each seven-gram portion of almonds reduced LDL cholesterol by 1%
  • This data suggests that nuts should be considered for inclusion in lipid-lowering diets.
Funding Source:
Reviewer Comments:
  • There was no washout period between treatments
  • The author does not describe the protocol very well: It does not sound like there were three groups that started the protocol at random times to receive the muffin, half or whole measure of almonds. If they had started with the muffin supplement and worked their way to the full almond supplement, results may reflect in part the long-term dietary compliance. 
  • The attrition rate is 37% and intent-to-treat statistics were not used. This in essence eliminates the effect of random selection: Results are based on those most interested in the study.
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
  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
  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
  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
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) Yes
 
Validity Questions
  1. Was the research question clearly stated? 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
  1.1. 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
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? Yes
  1.3. Were the target population and setting specified? Yes
  2. Was the selection of study subjects/patients free from bias? 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
  2.1. 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
  2.2. Were criteria applied equally to all study groups? Yes
  2.3. Were health, demographics, and other characteristics of subjects described? 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
  2.4. Were the subjects/patients a representative sample of the relevant population? Yes
  3. Were study groups comparable? 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) No
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) No
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? ???
  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
  3.3. 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
  3.4. 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
  3.5. 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
  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? No
4. Was method of handling withdrawals described? No
  4.1. Were follow-up methods described and the same for all groups? 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%.) No
  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%.) No
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? ???
  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
  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? N/A
5. Was blinding used to prevent introduction of bias? N/A
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? N/A
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? N/A
  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.) ???
  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.) ???
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? N/A
  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
  5.4. 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
  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. 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
  6.1. 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
  6.2. 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? ???
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? ???
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? ???
  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? N/A
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? N/A
  6.6. Were extra or unplanned treatments described? N/A
  6.6. 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? N/A
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? N/A
  6.8. In diagnostic study, were details of test administration and replication sufficient? N/A
  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. 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
  7.1. 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
  7.2. 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
  7.3. 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
  7.4. 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
  7.5. 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
  7.6. Were other factors accounted for (measured) that could affect outcomes? Yes
  7.7. Were the measurements conducted consistently across groups? 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. 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
  8.1. 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
  8.2. 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
  8.3. 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)? No
  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)? No
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? 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
  8.6. 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
  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? No
9. Are conclusions supported by results with biases and limitations taken into consideration? No
  9.1. Is there a discussion of findings? Yes
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? No
  9.2. Are biases and study limitations identified and discussed? No
  10. Is bias due to study's funding or sponsorship unlikely? ???
10. Is bias due to study's funding or sponsorship unlikely? ???
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? ???
  10.2. Was the study free from apparent conflict of interest? ???