PDM: Metabolic Syndrome (2013)
Mukuddem-Petersen J, Stonehouse (Oosthuizen) W, Jerling JC, Hanekom SM, White Z. Effects of a high walnut and high cashew nut diet on selected markers of the metabolic syndrome: A controlled feeding trial. British J Nutr. 2007; 97: 1,144-1,153.
PubMed ID: 17381974
To determine the effects of a high walnut diet and a high unsalted cashew nut diet on markers of metabolic syndrome compared to a control diet.
- ATP III criteria for the diagnosis of metabolic syndrome
- Subject’s ability to comply with the controlled feeding conditions
- Being willing and able to eat walnuts and cashew nuts
- 21 years of age and younger than 65 years.
- Pregnancy or lactation
- Taking thiazide medication (25mg per day)
- β-blocker (non-specific, β1 and β2) use
- Subjects having nut allergies
- Diagnosed diabetes.
68 white/Caucasian volunteers with metabolic syndrome were recruited from the Potchefstroom Campus of the North-West University and surrounding areas in Potchefstroom, South Africa.
Randomized, parallel, controlled trial.
- Study protocol consisted of a three-week run-in period where the subjects consumed a control diet
- After the run-in period, participants were grouped according to gender and age and then into three groups by randomly drawing numbers from a hat
- Group one received walnuts (N=21), group two received unsalted cashew nuts (N=21), group three continued with the control diet without any nuts or nut-based ingredients (N=22)
- The three intervention diets were followed for eight weeks
- All the food was provided to the participants for the duration of the trial
- Fasting blood samples, oral glucose tolerance tests, anthropometric measurements and blood pressure measurements were taken before (after the three-week run-in period) and after the intervention period (eight-week controlled feeding)
- BMI (kg/m2) was calculated
- The proportion of total energy (ranging from 63 to 108g per day) from nuts was 20%
- Except for the nuts, the diets were identical
- The study featured a highly controlled feeding protocol. All subjects were required to have their lunch at the metabolic ward of the Department of Nutrition at the Potchefstroom Campus of the North-West University. Breakfast and dinner were provided in take-away format.
- Using pre-packed food parcels and a variety of set menu options ensured compliance
- A validated FFQ and physical activity questionnaire measuring activity index were analyzed in order to determine the correct energy intake requirements for the maintenance of body weight for each participant
- A 14-day menu cycle was designed for five amounts of energy intake, ranging from 8,000 to 14,000kJ per day (1,905 to 3,333kcal per day)
- The macronutrient profiles and fatty acid distribution of the three diets were analyzed chemically to validate the diet composition
- Quality control and compliance with the protocol were ensured:
- Foods were weighed to the nearest gram before being served to the participants
- The principal investigator, a registered dietitian, supervised mealtimes and ensured the complete intake of all study foods
- Participants kept food diaries of the additional points used and possible leftovers were collected and weighed (by researchers)
- Participants were weighed twice weekly and the energy intake was adjusted (especially during the first three-week run-in period) in order to maintain body weight
- Participants were urged to maintain the same activity level throughout the study.
*** Individuals who used chronic medication (e.g., lipid-lowering medication) at baseline were instructed to continue use and to maintain the same dosage for the duration of the trial.
The statistical analysis was done in five steps:
- Variables were tested for normality using the Shapiro–Wilk’s W-test
- Descriptive statistics were done
- Data that were normally distributed are expressed as mean and 95% CI
- Data that are not normally distributed or logarithmic and square-root transformed are expressed as median (25th, 75th percentiles)
- For changes within groups, from baseline to end, a T-test for dependent samples was used for parametric data and the Wilcoxon matched-pairs test was used for non-parametric data
- Differences in baseline and D (change from baseline to end) between the three groups were determined by using the ANOVA for parametric data and the Kruskal–Wallis ANOVA for non-parametric data and the Tukey honest significant difference test was used for unequal N for parametric data
- Weight-adjusted differences in baseline and D between the three groups were determined by using the analysis of covariance
- With 80% power calculation, significance was set at P≤0.05.
Timing of Measurements
Baseline and at the end of the eight-week controlled feeding period.
- Lipid profiles
- Serum fructosamine and plasma glucose
- Blood pressure, uric acid and serum high-sensitivity C-reactive protein.
- Intervention diet high in walnuts
- Intervention diet high in unsalted cashew nuts.
- Initial N: 68
- Attrition (final N): N=64 (29 males, 35 women)
- Age: 21 years to 65 years (mean age: 45±10 years)
- Ethnicity: White/Caucasian
- Other relevant demographics: Mostly obese, sedentary and non-smokers
- Anthropometrics: Baseline anthropometrics were similar between the groups
- Location: Potchefstroom Campus of the North-West University, South Africa.
- Weight, BMI and waist circumference remained unchanged during the study
- Serum lipid concentrations showed no significant changes between walnut, cashew and the control groups
- Results from both nut groups showed no significant change in high-density lipoproteins, low-density lipoproteins, triglycerides or total cholesterol after the eight-week nut diet intervention
- There was no significant difference in serum fructosamine between the groups after the nut intervention
- Plasma glucose concentration (T=zero) increased significantly by 0.70mmol per L (P=0.04) in the cashew nut group compared to the control group
- No significant change was found in systolic and diastolic blood pressure, uric acid concentrations and C-reactive protein between the three groups after the eight-week nut diet intervention.
The authors concluded that individuals having metabolic syndrome showed no improvement in the markers of this syndrome after following a walnut diet or a cashew nut diet for eight weeks compared to a control diet while maintaining body weight.
|Government:||The National Research Foundation and the South African Government’s Technology and Human Resources for Industry Program|
- The methodology was sufficiently detailed with a high degree on quality and compliance control
- An eight-week nut intervention diet may not have been long enough to see significant change in the metabolic syndrome biomarkers
Specific detail on how the subjects were recruited was not identified
- Drawing numbers out of a hat is not a gold-standard method to use for randomization.
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?||Yes|
|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.)||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?||???|
|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?||No|
|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?||No|
|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)?||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?||???|
|9.1.||Is there a discussion of findings?||Yes|
|9.2.||Are biases and study limitations identified and discussed?||???|
|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|