CKD: Protein Requirements (2010)


Bernardi A, Biasia F, Pati T, Piva M, D'Angelo A, Bucciante G. Long-term protein intake control in kidney transplant recipients: Effect in kidney graft function and in nutritional status. Am J Kidney Dis. 2003; 41(S1): S146-S152.

PubMed ID: 12612973
Study Design:
Prospective Cohort Study
B - Click here for explanation of classification scheme.
Quality Rating:
Negative NEGATIVE: See Quality Criteria Checklist below.
Research Purpose:

Determine the long-term effect of dietary protein and salt restriction on renal function in patients with kidney transplants.

Inclusion Criteria:

Patients who received a renal transplant and had functional kidney at two months after surgical intervention.

Exclusion Criteria:

None given.

Description of Study Protocol:


Renal transplant patients at a single clinic from 1989 to 2002.


Prospective cohort study.


Dietary counseling for a diet with 30kcal per kg, a protein intake of 0.7g to 0.8g per kg per day, a salt intake of 3.0g per day, and a lipid intake of no more than 30% of the total energy intake was instituted.

Statistical Analysis

Descriptive statistics given in some results. Tests used to determine the significance of GFR, the primary outcome measure, were never stated. 


Data Collection Summary:

Timing of Measurement

Patients were observed monthly. At least every two months the patients had to keep a dietary diary for a period of two days (including weekends) with weighing method.

Dependent Variables

  • Glomerular filtration rate (calculated from serum creatinine, 24-hour urinary volume and body surface)
  • Serum creatinine
  • Lipid profile (total cholesterol, triglycerides, HDL)
  • Dietary protein: Calculated from 24-hour urinary urea
  • Dietary sodium: 24-hour urinary excretion
  • 13 anthropometric variables, 22 additional blood measures and three other urinary measures were done, but not included in the statistical analysis.

Independent Variables

  • Group 1: Diet compliant group (all patients who were compliant to dietetic prescriptions)
  • Group 2: Control group (no compliance).



Description of Actual Data Sample:
  • Initial N: 48 patients (36 men and 12 women)
  • Attrition (final N): 43 (five patients died)
  • Age: Men, 43.4+12.4 years; Women, 41.5+22.7 years
  • Ethnicity: Not stated, study done in Italy
  • Other relevant demographics: The mean duration of renal transplantation was 90.36+49.5 months for women and 81.68+59.2 months for men
  • Anthropometrics: No comparison of groups was done. Mean BMI, 24.8 (for men) and 24.1 (for women)
  • Location: Padua, Italy.



Summary of Results:

Note that the reviewer visually estimated the values in this table from figures in the article; no numbers for these variables were given in the table.


Diet Compliant  Group (N=30)

Control Group (N=18)

Statistical Significance of Group Difference

Change in Serum creatinine (mg percentage)


+ 0.8

Not given

Glomerular filtration rate (ml per minute)




Change in Lipids

  - Total cholesterol

  - Triglyceride

  - HDL 


-50 mg per dL

-50 mg per dL

+15 mg per dL


Not given

Not given

Not given


Other Findings:

  • Dietary protein in compliant group was 0.73g per kg per day compared to 1.4 in noncompliant group; sodium was 130mmol per day in compliant group compared to 190mmol per day in noncompliant group
  • During the 12 years of observation, five patients died of causes not related to renal transplant.
Author Conclusion:

Dietary restriction of protein and sodium can stabilize renal function in patients with kidney transplant.

Funding Source:
Reviewer Comments:

Appropriate statistical tests were not done. Presentation of key outcome data (GFR) was not given with the number of subjects at each yearly data point. Overall, this reviewer was completely uncertain as to the significance of the results. Potentially good study if it had been clearly presented and statistically analyzed.

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? ???
  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? ???
  2.2. Were criteria applied equally to all study groups? ???
  2.3. Were health, demographics, and other characteristics of subjects described? No
  2.4. Were the subjects/patients a representative sample of the relevant population? Yes
3. Were study groups comparable? ???
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) ???
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? ???
  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.) ???
  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? ???
  4.1. Were follow-up methods described and the same for all groups? N/A
  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? ???
  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? N/A
  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.) N/A
  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? Yes
  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? 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? ???
  6.6. Were extra or unplanned treatments described? ???
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? ???
  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? ???
  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? No
  8.1. Were statistical analyses adequately described and the results reported appropriately? No
  8.2. Were correct statistical tests used and assumptions of test not violated? No
  8.3. Were statistics reported with levels of significance and/or confidence intervals? No
  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? No
  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? No
  9.1. Is there a discussion of findings? ???
  9.2. Are biases and study limitations identified and discussed? No
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