DLM: Almonds (2009)

Citation:

Abbey M, Noakes M, Belling GB, Nestel PJ. Partial replacement of saturated fatty acids with almonds or walnuts lowers total plasma cholesterol and low-density-lipoprotein cholesterol. 1994. Am J Clin Nutr. 59 (5): 995-999.

 
Study Design:
Before-After Study
Class:
D - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:

To compare the effects of nuts with varying fatty acid content on plasma lipid levels.

Inclusion Criteria:
  • Males
  • Non-cholesterolemic.
Exclusion Criteria:

None specified.

Description of Study Protocol:
  • Recruitment: 20 males
  • Design: Cases series; non-comparative
  • Blinding used: None.

Intervention

  • Subjects followed a basal diet prescription over the duration of the study as follows: Background diet which provided 18% of energy from meat, diary, vegetable oils and fat spread. An additional 18% energy from fat was provided by a dietary supplement of nuts.
  • First three weeks' daily dietary supplement comprised of 50g raw peanut (25g fat); 40g coconut cubes (11g fat) and 50g confectionary bar containing coconut (11g fat)
  • Second three weeks' daily dietary supplement included 84g monounsaturated fatty acid rich raw almonds (46g fat)
  • Third three weeks' daily dietary supplement included 68g polyunsaturated rich walnuts (46g fat)
  • Subjects were given an additional three week supplement with walnuts.

Statistical Analysis

  • For the analysis of plasma lipids the average of three consecutive days' measurements taken at the end of each dietary period was used
  • Paired T-test was used as to determine significant differences.
Data Collection Summary:

Timing of Measurements

  • All samples were obtained at the end of each three-week interval
  • Food and beverage intake was recorded on three consecutive days during each three-week period
  • Fat sources and intake were recorded daily
  • Subjects were interviewed four times during each three-week period
  • Body weight was monitored at each clinic visit
  • Plasma was collected on three consecutive days and at the end of each three-week diet period, stored frozen, then analyzed at the end of the study.

Dependent Variables

  • Cholesterol and TG were measured on a Cobas-Bio automated centrifuge analyzer by standard enzymatic colormetric techniques with test kits
  • HDL-cholesterol was determined after precipitating apo-B containing lipoproteins with polyethylene glycol
  • LDL-cholesterol was calculated using modification of Friedlwald equation
  • Plasma, fatty and methyl esters were measured by gas chromatography
  • Nutrition intake was calculated from a computer database on Australian foods and direct food analyses (Diet Nutrient Calculation Software; Xyris software, Highgate Hill, Queensland, Australia).

Independent Variables

Dietary fatty acid.

Description of Actual Data Sample:
  • Initial N: 20 males
  • Attrition (final N): 16 males or 20% attrition
  • Age: 41±9 years
  • Ethnicity: Not disclosed
  • Other relevant demographics: Normocholesterolemic
  • Anthropometrics: Weight, 86.1±2.8kg
  • Location: Australia.
Summary of Results:

Table One: Plasma Fatty Acids After Three Weeks on Each of the Dietary Supplements1

Fatty Acid2

Reference Diet

Almond Diet
(Percentage)

Walnut Diet

14.0

1.00±0.07

0.86±0.083

0.83±0.08

16.0

21.8±0.41

21.03±0.55

21.18±0.48

16.1

2.78±0.28

2.39±0.253

2.34±0.223

18.0

6.98±0.22

65.94±0.17

6.98±0.19

18.1

24.66±0.78

26.20±1.20

21.35±0.894,5

18.2

30.45±1.02

30.48±0.96

34.86±1.044,5

18.3

0.49±0.04

0.53±0.05

1.27±0.124,5

20.3

1.58±0.05

1.59±0.06

1.42±0.053,6

20.4

6.99±0.33

6.91±0.35

6.49±0.287,8

20.5

0.80±0.06

0.73±0.06

0.95±0.076

22.5

0.65±0.04

0.64±0.04

0.71±0.04

22.6

1.80±0.15

1.70±0.12

1.64±0.10

1: X±SEM; N=16
2: Fatty acids of chain length under 14 were not detected. The number before the colon specifies the number of carbon atoms and that after the colon, the number of double bonds.
3,4,7: Significantly different from reference diet: 3, P<0.05; 4, P<0.001; 7, P<0.01
5,6,8: Significantly different from almond diet: 5, P<0.001; 6, P<0.01; 8, P<0.05.

Table Two: Plasma Lipid Levels After Three Weeks on Each of the Dietary Supplements2

  Reference Diet
(mmol/L)
Almond Diet
(mmol/L)
Walnut Diet
(mmol/L)
Total Cholesterol
5.17±0.24
4.81±0.232
4.92±0.232
LDL Cholesterol
3.58±0.24
3.20±0.223
3.26±0.223
HDL Cholesterol
0.96±0.06
0.96±0.06
0.99±0.06
Triglyceride
1.41±0.13
1.43±0.13
1.47±0.16

1: X±SEM; N=16
2,3: Significantly different from reference diet: 2, P<0.001; 3, P<0.001.
  • There was no significant change in plasma fatty acid composition after a further three-week of supplementation with walnuts
  • Significant reductions in total cholesterol (TC) and LDL-cholesterol after supplementation with 84g raw almonds and 68g raw walnuts (TC reduction, 7% and 5% and LDL-cholesterol, 10% and 9% with almonds and walnuts, respectively)
  • There were no significant differences in HDL cholesterol or triglyceride after any of the dietary intervention periods
  • Although almonds and walnuts were both effective in lowering cholesterol, it is possible that almonds may be more beneficial in reducing the risk of coronary heart disease
  • Plasma total cholesterol was significantly reduced after consumption of almonds or walnuts, as part of the diet for three weeks and this was maintained for a longer period
  • Fat intake was the same in each period although the fatty acid composition was different
  • There was no significant change in weight throughout the study.
Author Conclusion:

Dietary supplementation with almonds or walnuts lowers total plasma cholesterol and LDL-cholesterol.

Funding Source:
Government: Australian Horticultural Research and Development Corporation
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? No
  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? No
  2.2. Were criteria applied equally to all study groups? N/A
  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? No
3. Were study groups comparable? N/A
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) N/A
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? N/A
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) 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
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? Yes
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? No
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? Yes
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? 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.) 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? Yes
  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? N/A
  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? N/A
  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