DM: Protein Amount (2014)
The purpose of this study was to determine the effect of moderate dietary protein restriction on the progression of renal disease in a cohort of individuals with type 1 diabetes with diabetic nephropathy over a 6-month period.
1. Type 1 diabetes mellitus for >=10 yr
2. Proteinuria for >=2 yr
3. Presence of diabetic retinopathy
Recruitment: Subjects attending the renal diabetic clinical Johannesburg Hospital, South Africa were asked to participate.
Design:
Subjects were randomly assigned to an unrestricted protein diet (UPD)(>1.6 g/kg) or moderately restricted protein diet (LPD)(0.8 g/kg). Data collected at baseline and at 6 months.
Blinding Used (if applicable): not specified
Intervention (if applicable):
- Individuals were assessed by the same nutritionist at the start of the study at 3 and 6 months later.
- Usual Protein Group: ate their usual diets. Subjects with a low protein intake at the start of the study were asked to increase their protein intake to 1.6 gm/kg/day/.
- Low Protein Group: consumed an isoenergetic diet containing 0.8 g/kg/day protein.
- no distinctions made between animal and plant proteins.
- subjects were instructed on study diets and individualized based on usual food intake.
- no attempt was made to improve glycemic control
Statistical Analysis:
- Student's t test used for comprisons between groups
- changes within each group were compared using analyis of variance or Student's t tests
- Wilcoxon rank-sum test and signed-rank test used for nonparametric data where appropriate
- urine protein and albumin excretion reslults were logarithmetically transformed befor statistical analyis because of their positively skewed distribution
Timing of Measurements:
- GFR: Determined using 51Cr-labeled EDTA injection
- blood sampling at 5, 10, 20, 30, 60, 120, 180 and 240 minutes.
Dependent Variables:
- GFR
- urinary albumin excretion
- blood pressure
- glycemic control
Independent Variables
- Usual Protein Group: ate their usual diets. Subjects with a low protein intake at the start of the study were asked to increase their protein intake to 1.6 gm/kg/day/.
- Low Protein Group: consumed an isoenergetic diet containing 0.8 g/kg/day protein.
- Compliance assessed by
- comprehensive diet recall
- Monitoring of protein intake: calculated from total urea nitrogen as measured in a 24-h urine collection.
Control Variables: not specified
Initial N: 26
Final N: 22 subjects (11 in each group) completed the study—3 subjects were unable to comply with the study protocol and 1 subject was killed in an auto accident.
Age and Anthropometrics:
LPD n=11 | UPD n=11 | |
Age, yr | 30 | 29 |
BMI | 23.8 | 26.0 |
Duration of Diabetes, yr | 4 | 4 |
Ethnicity: white
Location: South Africa
Proteinuria and GFR
Patients consuming the UPD showed a progressive decrease in GFR of 1.3 ml/min/mo with no change in proteinuria.
Patients consuming the LPD showed a marked decrease in the degree of proteinuria (2.15-1.13 g/d, P=0.036) and a stabilization of GFR.
Urine urea protein:
Over the 6 month study period, urinary urea protein increased in the UPD group (425±136 to 720±122 mmol/d) (P=0.0004) and decreased in the LPD group (385±138 to 276±57 mmol/d ) (P<0.032).
Dietary assessment:
Protein intake was an average of data from 3 and 6 months:
Baseline g/kg
3 + 6 months g/kg
Significance
UPD
1.33
2.00
(P<0.0001)
LPD
1.13
0.87
(P=0.12)
Changes in GFR:
Baseline ml/min/1.73m2 |
3 + 6 months ml/min/1.73m2 |
Significance | |
UPD | 66±28 | 58±26 | (P<0.01) |
LPD | 50±19 | 53±23 | NS |
Changes in urinary albumin excretion:
Baseline mg/24 hour |
3 + 6 months mg/24 hour |
Significance | |
UPD | 1167 | 1475 | (P<0.01) |
LPD | 884 | 815 | (P=0.036) |
HbA1c
Glycemic control in these subjects showed a slight improvement over the study period (UPD from 13.9±2.4 to 12.4±5.5 and LPD from 12.0±3.4 to 11.7±4.6, normal range 4% to 8%).
Blood pressure:
Subjects in this study were hypertensive and there were no differences by time or group.
6 months study period
systolic mm Hg |
diastolic mm Hg |
MAP mm Hg |
|
UPD | 139±11 | 86±9 | 104±9 |
LPD | 140±12 | 91±6 | 107±7 |
Patients consuming the moderately restricted protein diet (0.8 g/kg) showed a marked decrease in the degree of proteinuria, and a stabilization of GFR independently of blood pressure or glycemic control.
Moderate dietary protein restriction can ameliorate progression of overt diabetic nephropathy.
Government: | South African Medical Research Council | ||
Industry: |
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Quality Criteria Checklist: Primary Research
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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%.) | 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)? | No | |
8.5. | Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? | ??? | |
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? | No | |
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? | Yes | |
10.1. | Were sources of funding and investigators' affiliations described? | Yes | |
10.2. | Was the study free from apparent conflict of interest? | Yes | |