CKD: MNT (2010)

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

This paper examines characteristics and behaviors associated with dietary adherence during the MDRD Study.

Inclusion Criteria:

Participants in the MDRD Study were adults with renal disease of diverse etiology.  They were divided into 2 groups based on the baseline GFR:

  • Study A included those with moderate renal insufficiency: GFR: 25 – 55 mL/min/1.73m2
  • Study B included those with advanced renal insufficiency: GFR: 13 – 24 mL/min/1.73m2

For this paper, these participants were categorized as either consistent adherers or nonadherers to the prescribed diet (see Study Design below).

Adherence was measured by estimated protein intake calculated from urinary urea nitrogen (UUN) excretion in monthly 24-hour urine collections and by protein intake reported from bimonthly 3-day food records.  The estimated protein intake value was considered the primary biological marker, and adherence ranges were established for each diet group based on the protein goals and intraindividual variablility of UUN levels.  Food record data was used to interpret the estimated protein intake values obtained.

For this study, adherers were defined as participants whose estimated protein intake values were in range and whose protein intakes from food records confirmed adherence to the protein goals for at least 4 of 6 adherence visits over the 2-year period of the trial.  Nonadherers were those whose estimated protein intake was out of range regardless of the reported dietary protein intake in at least 4 of the 6 adherence visits. 

Exclusion Criteria:

People on dialysis or with a history of kidney transplant were not included in the MDRD Study.

In this segment of the study, data from participants who missed 3 or more adherence visits, or those who had inconsistent adherence patterns, were excluded.

Description of Study Protocol:

Recruitment:  participants in the MDRD Study were categorized into adherers versus nonadherers for this paper.

Design: The MDRD Study was a RCT designed as a 2 x 2 factorial in order to evaluate effects of 3 dietary protein levels and 2 blood pressure levels.

Protein intake

  1. usual: 1.30 g/kg per day
  2. low: 0.58 g/kg per day
  3. very low: 0.28 g/kg per day plus keto-amino acid supplement (also 0.28 g/kg per day)

 Blood pressure levels

  1. usual: 107 mm Hg mean arterial pressure
  2. low: 92 mm Hg mean arterial pressure

Subjects in Study A were randomly assigned to either usual or low dietary protein and usual or low blood pressure goals.  Subjects in Study B were randomly assigned to either low or very low dietary protein and usual or low blood pressure goals.

Adherence range for protein in this study

  1. usual:  +25%                     (0.98-1.62 g/kg/day)
  2. low:  +30%                        (0.40-0.75 g/kg/day)
  3. very low: -20% - +50%     (0.22-0.42 g/kg/day)

Blinding Used:  no

Intervention:  The MDRD Study included a nutrition intervention program based on contemporary behavioral theories with the goal of promoting long-term adherence to the prescribed diet through self management with dietitian support.  Participant self-monitoring that included observation and recording of the target behavior (ie, protein intake) was an essential component. 

Statistical Analysis:  adherers compared to nonadherers in each diet group.  Comparison of continuous variables using one way ANOVA, categorical data using Chi-squared.  SPSS-X, version 4.0, 1993.

Data Collection Summary:

Timing of Measurements:  Adherence assessment every 4 months for the duration of the MDRD Study, with 6 adherence visits over a 2 year period.  The estimated protein intake was calculated from monthly UUN collections and protein intake estimated from bimonthly 3 day food records.  For this paper, the study period was 24 months.   

At baseline: age, gender, race, marital status, education, income, and standard weight.

Monthly and adherence visit data collection:

  • Weight, BMI, transferrin, and mean arterial pressure reported as means from 6 adherence visits and adjusted for baseline values.
  • Self-monitoring records collected and calculated monthly.
  • Use of special food products documented monthly.
  • Knowledge and skills rated monthly, other psychosocial characteristics rated at adherence visits.
  • Monthly recordings by RD of intervention strategies used by each participant.
  • GFR measured at 2 and 4 months and q 4 months thereafter.
  • Participant satisfaction at 6, 12 and 24 month.

At end of study, participants reported their perception of success and rated the usefulness of 19 intervention components that assisted in behavioral change.

Dependent Variables:  

  • Estimated protein intake calculated from 24 hour UUN excretion
  • Self-reported protein intake which defined adherence versus nonadherence to diet.

Independent Variables: 

  • Self-monitoring, psychosocial factors, intervention components and strategies related to dietary adherence.

Control Variables: 

  • Race
  • Marital status
  • Education
  • Gender
Description of Actual Data Sample:

Initial N:  840

Attrition (Final N): 

  • physiological characteristics reported, n=513
  • mean protein intake and diet behaviors reported, n=513
  • psychosocial ratings and intervention components, and intervention strategies reported, n=523                                 

Age:  mentioned elsewhere, not specific to this study.

Ethnicity:  mentioned elsewhere, not specific to this study.

Other Relevant Demographics:

Anthropometrics:  Weight and BMI reported for each group (mean + SD).

Location:  15 clinical centers in the United States.

Summary of Results:

All results are reported comparing adherers to nonadherers in each diet group.

 

Usual protein diet

(N=294)

 

Low protein diet, study A

(N=291)

 

Low protein diet, study B

(N=129)

 

Very low protein diet

(N=126)

 

Physiological characteristics, reported mean protein intake and dietary behaviors

Adherers (n=147)

Nonadherers (n=27)

Adherers(n=101)

Nonadherers (n=83)

Adherers (n=59)

Nonadherers (n=19)

Adherers (n=31)

Nonadherers (n=46)

Selected psychosocial factors, intervention components and intervention strategies

Adherers (n=147)

Nonadherers (n=27)

Adherers(n=101)

Nonadherers (n=93)

Adherers (n=59)

Nonadherers (n=19)

Adherers (n=31)

Nonadherers (n=46)

As expected by definition, those in the adherers groups had estimated protein intake values within range, as well as self-reported protein calculated from 3-day food records.  Nonadherers were out of range for estimated protein intake values, despite reported dietary protein being in range.

Significant differences (p<0.01) noted between adherers and nonadherers in low-protein A group for mean weight, BMI and transferrin levels. 

Mean protein intake from self-monitoring was significantly lower between adherers and nonadherers in low-protein A (p<0.001), low-protein B (p<0.05), and very-low-protein (p<0.01) groups.

Frequency of self-monitoring and percentage of those who frequently self-monitored was higher in all 4 groups of adherers.

Knowledge and skills (p<0.001), attitude toward eating pattern (p<0.001), and effect of health on eating pattern was rated significantly higher by the RD in all 4 groups of adherers.

Social support was rated significantly higher by the RD in 3 groups of adherers.

Perceived success was rated significantly higher (p<0.001)  by the participants in all 4 groups of adherers.

Usefulness of RD support and usefulness of self-monitoring was rated significantly higher by the participants in 3 groups of adherers.

Specific intervention strategies rated significantly higher in 3 or 4 groups:

  • review of weighing and measuring skills
  • providing guidelines for increasing energy
  • providing guidelines for protein modification
  • reviewing flowsheet of adherence or biochemistry data
  • chosing not to discuss urinary markers of protein intake
  • conducting (monthly) telephone calls
Author Conclusion:

The MDRD Nutrition Intervention Program emphasized using a positive approach to obtaining healthful long-term eating patterns. 

Self-monitoring helped participants achieve dietary protein goals.

Focusing on psychosocial factors and behavioral approaches can help the RD promote adherence.  It is recommended to incorporate self-management strategies, particularly self-monitoring and the provision of feedback and support into nutrition intervention programs.

 

Funding Source:
Government: NIDDK, Health Care Financing Administration, NIH
Reviewer Comments:

Attrition in all groups was noted but not described in sufficient detail.

The authors note that "for the analyses in this article, only data on the basic type of self-monitoring are reported"  but this statement is not explained.

The authors note that both dietitian and participant ratings were completed with knowledge of the participants' estimated protein intake values.  Dietitians were encouraged to be objective and nonjudgemental when completing subjective assessments related to adherence.

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%.) N/A
  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? ???
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? ???
  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.) ???
  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? ???
  7.6. Were other factors accounted for (measured) that could affect outcomes? ???
  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? ???
  8.1. Were statistical analyses adequately described and the results reported appropriately? ???
  8.2. Were correct statistical tests used and assumptions of test not violated? ???
  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)? No
  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? ???
10. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? ???
  10.2. Was the study free from apparent conflict of interest? Yes