DM: Prevention and Treatment of CVD (2007)

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

1. To investigate the effects of increased nut consumption on insulin sensitivity in free-living healthy persons.

2. To test the hypothesis that an increased nut consumption produces greater benefits than do high-MUFA oils on serum lipids and lipoproteins and glycemia in patients with type 2 diabetes.

Inclusion Criteria:

Study 1

  • normal blood chemistry values
  • normal hematocrit
  • fasting glucose concentration <6.67mmol/l

Study 2

  • type 2 diabetes previously diagnosed by a physician or fasting glucose >7.8 mmol/l
  • moderately good glucose control:  fasting glucose < 11.1 mmol/l
Exclusion Criteria:

Study 2

  • insulin therapy
  • taking medications to lower cholesterol
  • clinically significant neuropathy, nephropathy, or CVD
  • LDL > 5.2 mmol/l
  • fasting triacylglycerol > 7.8 mmol/l
  • HDL < 0.65 mmol/l
  • pregnancy, lactation, or allergy to nuts
Description of Study Protocol:

Recruitment : not specified

Design

Study 1:  4 weeks of dietary supplementation of 100 mg/day (about 1 cup)

Study 2: subjects were randomly assigned to 1 of 4 diet arms with a minimum 2-week break between diet periods

Blinding used (if applicable):  not possible - lab tests

Intervention (if applicable)

Study 1

  • almonds were provided whole or in trail mix, muffins, or cookies
  • subjects were told how many calories were in 100g of almonds and were encouraged to reduce their energy intakes by an equivalent amount
  • subjects completed a 3-day food diary each week for assessment of compliance

Study 2 diet periods

  • high-fat high almond (HFA; 37% total fat, 10% from almonds)
  • low-fat high almond (LFA; 25% total fat, 10% from almonds)
  • high-fat control (HFC; 37% total fat, 10% from the MUFAs olive oil or canola oil
  • low-fat control (LFC; 25% total fat, 10% from olive or canola oil)
  • subjects were provided with all foods needed for the duration of the study.  On weekdays, the subjects were required to consume breakfast and dinner at the Research Center dining facility.  Weekday lunches, snacks, and weekend meals were packaged for take-out.

Statistical Analysis

Study 1

  • analysis of variance with repeated measures used to compare outcome variables before and after the almond supplementation period

Study 2

  • a two-factor ANOVA with repeated measures cholesterol, lipoproteins, glucose, and insulin concentrations at the end of each diet period
  • factors were fat source and fat level and all analyses were adjusted for energy intake

 

 

 

Data Collection Summary:

Timing of Measurements

  • whole-body insulin sensitivity measured at enrollment
  • lab values measured at baseline and at end of diet intervention periods

Dependent Variables

  • total cholesterol
  • HDL and HDL particle size
  • insulin
  • blood glucose
  • HbA1c

Independent Variables

  • dietary intake, fat vs almonds
  • foods provided

Control Variables

  • sex
  • energy intake

 

Description of Actual Data Sample:

Initial N:

  • Study 1: 20; 10 healthy men and 10 healthy premenopausal women
  • Study 2: 34 men and women with type 2 diabetes; 17 women, of these 14 were postmenopausal and 11 were taking hormone replacement therapy

Attrition (final N):

Study 1:  all enrolled subjects completed the study

Study 2:  30 of 34 completed the study

Age:

  • Study 1:  25.1 ± 1 y
  • Study 2:  53.8 ± 1.9 y

Ethnicity:

  • Study 2:  12 subjects were African American, remainder were white

Other relevant demographics:

Anthropometrics

Study 1:  BMI 23 ± 0.3

Study 2:  BMI 33.0±1.0

Location: United States

 

Summary of Results:

Study 1:  Changes in healthy volunteers after 4-wk supplementation with almonds

Variables

Before

 

After

  P P P
   Men  Women  Men  Women  Main effect of time Main effect of sex Sex-by-time interaction

body weight, kg

 77.2±2.3 57.5±2.3  78.1±2.33  57.8±2.3   0.006  0.0001  NS

fasting glucose, mmol/l

 5.16±0.11

4.90±0.11 

5.17±0.11 

5.05±0.11 

 NS

 NS  NS

fasting insulin, pmol/l

 33.6±4.2

34.8±4.2 

38.4±4.2 

34.8±4.2 

 NS

 NS  NS
insulin sensitivity index  3.31±0.41 4.75±0.41  3.73±0.41  3.85±0.41  NS  NS  0.04

glucose effectiveness

 2.14±0.17 2.71±0.17   2.38±0.17 2.33±0.17   NS  NS  0.006
cholesterol, mmol/l  4.50±0.18 4.75±0.18  3.59±0.18  3.70±0.18   0.0001  NS  NS
LDL, mmol/l  3.01±0.16 3.02±0.16  2.22±0.16  2.10±0.16   0.0001  NS  NS
HDL, mmol/l  1.0±0.05 1.4±0.05  0.88±0.05  1.22±0.11   0.0002  0.0001  NS
triacylglycerols, mmol/l  1.02±0.11 0.76±0.11  0.99±0.11  0.79±0.11   NS  NS  NS
LDL:HDL  3.02±0.20 2.37±0.02  2.54±0.20  1.76±0.20   0.0005  0.01  NS
total cholesterol:HDL  4.51±0.24 3.65±0.24  4.11±0.24  3.08±0.24   0.003  0.006  NS

 Study 2  Lab values after high- and low-fat diets enriched with almonds or refined oils in 30 subjects with type 2 diabetes 1

Variable Diet       P P P
  HFA HFC LFA LFC Main effect of fat source Main effect of fat level Interaction(fat source by fat level)
total cholesterol, mmol/l  4.46±0.14 4.52±0.14  4.63±0.14  4.63±0.14   NS  0.0004  NS
LDL, mmol/l  2.51±0.10 2.58±0.10  2.53±0.10  2.53±0.10   0.06  NS  NS
HDL, mmol/l  1.13±0.04 1.17±0.04  1.13±0.04  1.16±0.04   0.002  NS  NS
triacylglycerols, mmol/l  1.77±0.18 1.68±0.18  2.10±0.18  2.0±0.18b   NS  0.0001  NS
total cholesterol:HDL  4.1±0.1 4.0±0.1  4.2±0.1  4.2±0.1   0.06  0.0002  NS
fasting gluose, mmol/l  8.14±0.49 8.73±0.48  8.63±0.48  8.00±0.49   NS  NS  0.006
2-h glucose, mmol/l  15.2±0.7a,b 15.7±0.7a  15.7±0.7a 14.6±0.7b   NS  NS  0.008

1 Least-squares mean ± SEM adjusted for total energy intake.

a,b Means with different superscript letters are significantly different, P<0.01.

Other Findings

Study 1:  total energy intake increased slightly, but not significantly. Fat intake increased significantly and carbohydrate intake decreased significantly.  Saturated fat intakes remained unchanged.

Study 2:  There were no significant effects of fat source, fat level, or fat source by fat level on  LDL:HDL ratio, HDL fractions, fasting insulin, 2-h insulin or HbA1c.

 

Author Conclusion:

In healthy adults (study 1) the increase in nut consumption did not substantially influence insulin sensitivity.  Despite a significant increase in body weight, total cholesterol, HDL, and LDL decreased significantly after almond consumption.

In patients with diabetes (study 2) almond-enriched diets significantly decreased HDL.  Almond diets didn not alter glycemia relative to control diets.

In summary

  • almonds have no effect on insulin sensitivity in normal adults, nor do they affect glycemia in patients with type 2 diabetes.  Low-fat diets, regardless of the fat source have no adverse effects on glycemia or insulinemia in patients with type 2 diabetes.
  • almonds reduce serum cholesterol concentrations in healthy persons
  • almonds decreased HDL in both healthy subjects and those with diabetes
Funding Source:
Reviewer Comments:
Recruitment methods unclear.  This study was supported by the Almond Board of California.  Authors note that significant body weight increase in healthy adults may have masked changes in insulin sensitivity.  Authors also note that in Study 2, population was somewhat unusual in that subjects had fairly low cholesterol and and LDL cholesterol at enrollment.
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? No
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? 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? 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)? No
  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? 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? No
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? No