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PDM: Prediabetes (2013)

Citation:

Wien M, Bleich D, Raghuwanshi M, Gould-Forgerite S, Gomes J, Monahan-Couch L, Oda K. Almond consumption and cardiovascular risk factors in adults with prediabetes. J Am Coll Nutr. 2010; 29(3): 1,189-1,197.
 

PubMed ID: 20833991
 
Study Design:
Randomized Controlled Trial
Class:
A - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:

To test the hypothesis that an almond-enriched American Diabetes Association diet (ADA) would be more effective than a nut-free ADA diet on improving measures of insulin sensitivity in individuals with prediabetes.

Inclusion Criteria:
  • Presence of prediabetes according to the 2005 ADA diagnostic guidelines (fasting blood glucose between 100mg and 125mg per dL or casual blood glucose 140mg to 199mg per dL or more), body mass index (BMI) 20 to 35kg/m2 and willingness to discontinue vitamin E supplement usage
  • Provided written informed consent.
Exclusion Criteria:
  • Self-reported allergy to almonds
  • History of irritable bowel disease or diverticulitis
  • Use of corticosteroids or immunosuppressant medications
  • Presence of liver disease, renal disease and severe dyslipidemia [triglyceride (TG) higher than 400mg per dL or TC higher than 300mg per dL].
Description of Study Protocol:

Recruitment

Subjects were recruited from a pool of adult employees at University of Medicine and Dentistry of New Jersey (UMDNJ), Newark, New Jersey.

Design

Parallel group randomized trial.

Blinding Used

Implied with measurements.

Intervention

16 weeks of dietary modification featuring an American Diabetes Association diet (ADA) diet containing 20% of energy from almonds (approximately two oz per day, an added 5g per day of dietary fiber), compared to a nut-free diet.

Statistical Analysis

  • Sample size and power calculations were performed using SAS version 9.1
  • Data were entered into an SPSS version 12.0 database and statistical analysis was performed using SPSS and SAS
  • Bivariate statistical analysis using the chi-square test for differences in proportions and two-sided independent T-tests were performed on baseline characteristics using a probability value of 0.05
  • To assess the significance of changes in anthropometric and metabolic variables, a mixed-model repeated measures analysis of covariance was used with diet, week and diet x week interaction as fixed effects, adjusting for baseline measurements of the outcome variable
  • A natural log transformation was performed on outcome variables for the modeling analysis when indicated to improve normality and the results were exponentiated for reporting purposes
  • Additional analyses for glucose, insulin, HOMA-IR and HOMA-B models were performed and adjusted for weight by adding the baseline weight as a covariate
  • An intent-to treat analysis was performed and all percentage change values presented are calculated from least-squares means (LSM) estimated from mixed models
  • Week zero, eight and 16 measurements were included in the analysis with the exception of weight, BMI, WC and BP that included additional measurements from weeks four and 12.

 

Data Collection Summary:

Timing of Measurements

Measurements made at baseline, week eight and week 16.

 Dependent Variables

  • Fasting glucose, insulin, TC, LDL-C, high-density lipoprotein cholesterol (HDL-C), TG, TC:HDL-C and HbA1c; measured by venous blood samples collected at the New Jersey Medical School general clinical research center after a 12- to 14-hour fast at weeks zero, eight and 16. Serum glucose, insulin, TC, LDL-C, HDL-C, TG and HbA1c was measured by the UMDNJ University Hospital Clinical Laboratory. Serum insulin levels were measured using direct enzyme linked immunosorbent assay methods.
  • Plasma alpha tocopherol concentrations were evaluated as a marker of almond consumption compliance; measured by LabCorp using high-performance liquid chromatography with fluorometric detection
  • Height was measured to the nearest centimeter using a stadiometer
  • Weight and blood pressure were obtained at each clinic visit. Weight was measured using an internally calibrated segmental body composition scale/analyzer and recorded to the nearest 0.01 lb
  • BMI was calculated as weight (kg)/height (m2)
  • Blood pressure was measured using a calibrated automated digital monitor.
  • Waist circumference was measured to the nearest 0.1cm midway between the last rib and the ileac crest.

Independent Variables 

  • Participants in the intervention arm consumed an American Diabetes Association diet with 20% of energy from almonds and avoided other tree nuts and peanuts. The diet was consumed for 16 weeks and contained 15% to 20% protein, less than 10% saturated fat, 60% to 70% carbohydrate and MUFA and cholesterol less than 300mg per dL.
  • A three-day food and activity record (two weekdays and one weekend day) was requested from participants one week prior to the start of the study. At week zero, participants met with the study dietitian for a one-hour counseling session to receive their individualized ADA diet. The intervention group received instruction on how to select 80% of their energy needs using the ADA Food Exchange System.
  • Intervention participants were instructed only to consume prepackaged study almonds
  • Self-reported dietary intake was also examined in the context of changes from baseline to the second eight weeks of the study. A three-day food and activity record was completed by each participant at weeks four, eight, 12 and 16. The study dietitian reviewed the records according to the prescribed number of ADA food exchanges and provided reinforcement. Records were analyzed using the US Department of Agriculture database.

 

Description of Actual Data Sample:
  • Initial N: 65 total, 32 in the intervention group (22 females, 10 males), 33 in the control group (26 females, seven males)
  • Attrition (final N): 54 total, seven withdrew from the intervention arm and four from the control arm
  • Age: Mean age in the intervention group was 53±9 years and 54±11 years in the control group.

Ethnicity

  • 38% Caucasian in the intervention group and 40% in control group
  • 12% Hispanic in the intervention group and 15% in the control group
  • 44% African American in the intervention group and 27% in control group
  • 6% Asian in the intervention group and 18% in the control group.

Other Relevant Demographics

Mean fasting glucose in intervention group 101±13mg per dL, mean fasting glucose in the control group 104±14mg per dL.

Anthropometrics

Mean body mass index in the intervention group 30±5kg/m2, mean body mass index in the control group was 29±5kg/m2. Participants randomized into the intervention and control arms were similar in terms of baseline characteristics.

Location

Newark, New Jersey.

 

Summary of Results:

Key Findings

  • The mean intake of almonds for participants in the intervention group was 60g per day
  • A small weight loss was experienced by both groups (the intervention group lost 1.1kg and the control group lost 2kg of weight), but there were no significant changes in BMI, weight, fasting glucose, A1C, triglycerides, HDL cholesterol, waist circumference or systolic or diastolic blood pressure between groups during the trial
  • The almond-enriched intervention group exhibited greater reductions in insulin (-1.78uU per ml vs. +1.47uU per ml, P=0.002, homeostasis model analysis for insulin resistance (-0.48 vs. +0.30, P=0.007) and homeostasis model analysis for beta-cell function (-13.2 vs. +22.3, P=0.001) compared with the nut-free control group
  • Clinically significant declines in LDL-C were found in the almond-enriched intervention group (-12.4mg per dL vs. -0.4mg per dL) as compared with the nut-free control group.

 

 

 

 

Author Conclusion:

An American Diabetes Association (ADA) diet consisting of 20% of calories as almonds over a 16-week period is effective in improving markers of insulin sensitivity and yields clinically significant improvements in LDL-C in adults with prediabetes.

Funding Source:
Industry:
Almond Board of California
Commodity Group:
Reviewer Comments:

The authors noted that this study is not without limitations. The sample size was small and it is possible that error may have existed in the participants self-reported dietary intakes. Also, even though the participants were instructed to consume equivalent amounts of energy from carbohydrates, there was a difference in self-reported carbohydrate intake between the two groups. Sponsored by the Almond Board of California.

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? 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? No
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? 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? Yes
  6.6. Were extra or unplanned treatments described? Yes
  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)? 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
  8.7. If negative findings, was a power calculation reported to address type 2 error? Yes
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? ???