Nuts - CNPP (DGAC)

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

To assess the effect of almonds on antioxidant vitamins and lipid markers of oxidative damage, including serum malondialdehlyde (MDA) and urinary isoprostane output, to determine whether the antioxidant property of almonds may be a further reason for their cardioprotective effects. 

Inclusion Criteria:

Healthy hyperlipidemic men and post-menopausal women.

Exclusion Criteria:
Description of Study Protocol:

Recruitment

Newspaper advertisement and patients attending the Risk Factor Modification Center.

Design

Randomized crossover.

Intervention (if applicable)

Three one-month diet phases consisting of a muffin phase (control) and two almond phases: One full-dose almond and the other half-dose almond plus half-dose muffin (half-dose almond). 

Statistical Analysis

Mixed models were constructed to assess the effect of diet on serum and urinary measures at week four. All models included diet, total cholesterol, gender, diet sequence and the interactions between gender and diet and gender and cholesterol.  The final model included subjects as random factor, gender, diet sequence, interactions between gender and diet and gender and sequence, and baseline serum measures as a covariate. Diet sequence and interactions were removed from the final models if they were not significant. When diet was significant, post-hoc contrasts were used to compare outcomes between the three diets. A Tukey adjustment was made for multiple means comparisons. 

Data Collection Summary:

Timing of Measurements

  • Baseline and at week two and four of each four-week diet phase for weight, blood and blood pressure
  • 24-hour urine sample at the end of week four
  • Seven-day weighed food records prior to baseline and at week four of each phase.

Dependent Variables

  • Diet: Seven-day weighed food diaries with subjects instructed to weigh all foods eaten with the self-taring electronic scales provided. The records were analyzed using the USDA database. The percentage for soluble and insoluble fiber were derived from published data. 
  • Blood: Drawn after overnight fast for serum vitamin A, α- and y-tocopherol, MDA. These and  the urinary isoprostanes were analyzed by reverse phase HPLC.
  • Urinary creatinine: Analyzed in the routine clinical laboratory.

Control Variables

Prior to the study, all subjects had been instructed on the NCEP Step 2 diet for two months. One of three supplements: 73±2g per day of whole raw unblanched almonds; muffins (147±6g per day) and half portion of almonds (37±2g per day) plus muffins (75±3g per day). The muffins were made from whole-wheat flour with corn oil sufficient to provide the same amount of SFA, PUFA and fiber as the almonds, and with skim-milk powder and egg white to provide a similar level of protein, although the muffin protein was 46% of animal origin. MUFA from almonds balanced the starch from muffins. Subjects were told to reduce total food intake, especially starchy foods, to allow supplements to be eaten as snacks without increasing total energy intake and to keep the background diet constant across all three phases. Subjects were asked to not eat any additional nuts or nut products or alter consumption of dietary fiber or vegetable protein foods. Uneaten supplements were to be returned. Study supplements were analyzed using AOAC methods for fat, protein and fiber. Available carbohydrate was calculated as total carbohydrate minus fiber. The fatty acid composition was determined by GC.

Description of Actual Data Sample:

 

  • Initial N: 43
  • Attrition (final N): 27 (15 men, 12 women)
  • Age: 64±9 years (range, 48 to 86 years) 
  • Anthropometrics: BMI, 25.5±4.0kg/m2 (range, 20.5kg/m2 to 31.5 kg/m2); LDL-C, 4.32±0.63mmol per L (range, 2.77 to 5.32) and TG less than 4.0mmol per L. None used tobacco or had biochemical evidence of diabetes, or liver or renal disease. Of the three men and five women taking medication, all had been stable on them for two weeks prior to the study. 
  • Location: Toronto, Canada.
Summary of Results:

 

Variables

Week

Control

Half-almond

Full-almond

Body weight (kg)

0

 71.0±2.4

 71.1±2.4

 71.2±2.5

Body weight (kg)

4

 71.2±2.5a

 70.9±2.4b

 71.0±2.5ab

Total cholesterol (mmol per L)

0

 6.54±0.16

 6.47±0.15

 6.60±0.16

Total cholesterol (mmol per L)

Treatment  6.44±0.15a  6.25±0.15b  6.21±0.15b
LDL-C (mmol per L) 0  4.34±0.14  4.30±0.12  4.45±0.13
LDL-C (mmol per L)  Treatment  4.22±0.13a  4.10±0.12ab  4.01±0.12b
HDL (mmol per L) 0  1.43±0.09  1.38±0.08  1.40±0.08
HDL (mmol per L)  Treatment  1.41±0.08b  1.43±0.08ab  1.45±0.09a
Energy, kcal 4 1,900±89  1,951±94  2,034±98
Total protein, % 4  17.5±0.5  17.6±0.5  17.4±0.4
Vegetable protein, % 4  7.2±0.3b  7.8±0.3ab  8.7±0.3a
Available CHO, % 4  54.5±1.1a  48.4±1.1b  44.8±1.2b
Total diet fiber, g per 1000kcal 4  16.3±1.1  16.5±0.9  16.4±0.9
Total fat, % 4  26.3±1.0c  32.1±1.0b  36.0±1.0a
 SFA, % 4  7.0±0.4  7.5±0.4  7.2±0.4
 MUFA, %  9.0±0.5c  14.5±0.5b  18.9±0.6a
 PUFA, % 4  8.0±0.3  8.0±0.3  8.2±0.2
 Diet cholesterol, mg per 1000 kcal 4  88.7±7.3  96.8±6.2  79.3±5.3
 Alcohol, % 4  1.8±0.5  1.9±0.5  1.8±0.6

Values  are means±SEM. Means in a row with superscripts without a common letter differ, P<0.05. 

Other Findings  

Compliance with the supplement was 97.8±0.7% to 99.5±0.6% for all three treatments. 

Serum MDA decreased during the full-dose almond intervention and differed from the change during the control period (P=0.040). The baseline MDA concentration was a significant predictor of the treatment effect (P=0.002). The overall diet effect approached significance (P=0.051). 

After creatinine correction, urinary isoprostane outputs during the half- and full-dose almond treatments were lower than during the control treatment (P<0.03). The diet x gender interaction was not significant for urinary isoprostane output (P=0.415). 

The serum levels of α- or y-tocopherol and other vitamins were not affected by the treatments. 

Author Conclusion:

The antioxidant potential of almonds was demonstrated as reductions in serum MDA and urinary isoprostanes as markers of lipid peroxidation. It is likely that the antioxidant property of almonds was related to the effect of flavonoids and other phenolic antioxidants and the high MUFA content of almonds. 

Funding Source:
Industry:
Reviewer Comments:
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? 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? ???
  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.) 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
  5.5. 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? 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? 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? ???
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? ???