CKD: Protein Requirements (2010)


Bernardi A, Biasia F, Pati T, Piva M, Scaramuzzo P, Stoppa F, Bucciante G. Factors affecting nutritional status, response to exercise and progression of chronic rejection in kidney transplant recipients. J Renal Nutrition. 15 (1): 54-57, 205.

PubMed ID: 15648008
Study Design:
Cohort study
B - Click here for explanation of classification scheme.
Quality Rating:
Negative NEGATIVE: See Quality Criteria Checklist below.
Research Purpose:

Determine the associations of protein intake and response to exercise to progression of chronic rejection in kidney transplant patients.

Inclusion Criteria:

Patients who received a kidney transplant and had functional kidney at 20 months after surgical intervention.

Exclusion Criteria:

None given.

Description of Study Protocol:
  • Recruitment: Renal transplant patients at a single clinic from 1989 to 2002
  • Design: Prospective cohort study
  • Blinding used (if applicable): N/A 
  • Intervention: 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 less than five grams per day and a lipid intake of no more than 30% of total energy intake was instituted. Groups were formed by dietary compliance.
  • Statistical analysis: None given, although glomerular filtration rate was stated as "significantly significant" in the figure legend.
Data Collection Summary:

Timing of Measurements

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

Dependent Variables

  • Glomerular filtration rate (calculated from serum creatinine, 24-hour urinary volume and body volume)
  • Maximal exercise test (VO2 uptake and VCO2 production; 20 patients).

Independent Variables

  • Group One: Diet compliant group (all patients compliant to dietetic prescriptions)
  • Group Two: Non-compliant.

Control Variables


Description of Actual Data Sample:
  • Initial N: 86 patients (67 men and 19 women)
  • Attrition (final N): None stated
  • Age: Men, 44.3±14.3 years; women, 42.3±23.9 years
  • Ethnicity: Not stated; study done in Italy
  • Other relevant demographics: The mean duration of renal transplantation was 104.4±42.5 months for women and 93.7±53.2 months for men
  • Anthropometrics: No comparison of groups were given. Mean BMI, 24.8 for men and 24.1 for men.
  • Location: Pauda, Italy.
Summary of Results:

[Note: The reviewer visually estimated  the variables in this table from figures in the article; no numbers for these variables were given in the article.]

Variables Compliant Group
(N=68 at Vaseline)
Non-Compliant Group
(N=18 at Baseline)
Statistical Significance of
Group Difference
Change in Glomerular Filtration Rate (ml/min) from Baseline to 14-Year Follow-Up +5 (from 65 to 70) -29 (from 71 to 42) e.g., P=<0.001

Other Findings

  • 20 patients with a renal transplant had a higher increase than healthy controls in energy expenditure during work (data not given). VO2 uptake and VCO2 production were higher in transplant patients than healthy controls.
  • Urinary sodium excretion was 130mmol per day for the compliant group vs. 200mmol per day for the control group, respectively.
Author Conclusion:

The reduction of obesity and of cardiovascular risk factors in renal transplant patients are goals to be obtained by adequate nutrition, exercise and physical activity. 

Funding Source:
Reviewer Comments:
  • The author conclusions on exercise are not supported by the data given in this article
  • The difference that dietary modification makes has been previously reported in greater detail by the same authors (Am J Kidney Dis. 2003, 41: S146-S152)
  • No statement of how the statistical analyses was done
  • Major omission is the number of subjects at each of the years' points presented in the GFR figure
  • Obviously, not all subjects survived the 14-year length of the study.
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? ???
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? ???
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? ???
  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? No
  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? No
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) No
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? No
  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? No
  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.) No
  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? No
  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%.) No
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? ???
  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? No
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? N/A
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? Yes
  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? No
  6.6. Were extra or unplanned treatments described? No
  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