Protein-restricted diets in diabetic nephropathy

Low protein diets for chronic kidney disease in non diabetic adults

BACKGROUND

For more than fifty years, low protein diets have been proposed to patients with kidney failure. However, the effects of these diets in preventing severe kidney failure and the need for maintenance dialysis have not been resolved.

OBJECTIVES

To determine the efficacy of low protein diets in delaying the need to start maintenance dialysis.

SEARCH STRATEGY

Cochrane Renal Group studies register, the Cochrane Central Register of Controlled studies, MEDLINE, and EMBASE. Congress abstracts (American Society of Nephrology since 1990, European Dialysis Transplant Association since 1985, International Society of Nephrology since 1987). Direct contacts with investigators.

SELECTION CRITERIA

Randomised studies comparing two different levels of protein intake in adult patients suffering from moderate to severe kidney failure, followed for at least one year.

DATA COLLECTION AND ANALYSIS

Two authors independently selected studies and extracted data. Statistical analyses were performed using the random effects model and the results expressed as risk ratio (RR) for dichotomous outcomes with 95% confidence intervals (CI). Collection of the number of "renal deaths" defined as the need for starting dialysis, the death of a patient or a kidney transplant during the study.

MAIN RESULTS

Ten studies were identified from over 40 studies. A total of 2000 patients were analysed, 1002 had received reduced protein intake and 998 a higher protein intake. There were 281 renal deaths recorded, 113 in the low protein diet and 168 in the higher protein diet group (RR 0.68, 95% CI 0.55 to 0.84, P = 0.0002). To avoid one renal death, 2 to 56 patients need to be treated with a low protein diet during one year.

AUTHORS' CONCLUSIONS

Reducing protein intake in patients with chronic kidney disease reduces the occurrence of renal death by 32% as compared with higher or unrestricted protein intake. The optimal level of protein intake cannot be confirmed from these studies.

Protein restriction for diabetic renal disease

BACKGROUND

Diabetic renal disease (diabetic nephropathy) is a leading cause of end-stage renal failure. Once the process has started, it cannot be reversed by glycaemic control, but progression might be slowed by control of blood pressure and protein restriction.

OBJECTIVES

To assess the effects of dietary protein restriction on the progression of diabetic nephropathy in patients with diabetes.

SEARCH STRATEGY

We searched The Cochrane Library, MEDLINE, EMBASE, ISI Proceedings, Science Citation Index Expanded and bibliographies of included studies.

SELECTION CRITERIA

Randomised controlled trials (RCTs) and before and after studies of the effects of a modified or restricted protein diet on diabetic renal function in people with type 1 or type 2 diabetes following diet for at least four months were considered.

DATA COLLECTION AND ANALYSIS

Two reviewers performed data extraction and evaluation of quality independently. Pooling of results was done by means of random-effects model.

MAIN RESULTS

Twelve studies were included, nine RCTs and three before and after studies. Only one study explored all-cause mortality and end-stage renal disease (ESRD) as endpoints. The relative risk (RR) of ESRD or death was 0.23 (95% confidence interval (CI) 0.07 to 0.72) for patients assigned to a low protein diet (LPD). Pooling of the seven RCTs in patients with type 1 diabetes resulted in a non-significant reduction in the decline of glomerular filtration rate (GFR) of 0.1 ml/min/month (95% CI -0.1 to 0.3) in the LPD group. For type 2 diabetes, one trial showed a small insignificant improvement in the rate of decline of GFR in the protein-restricted group and a second found a similar decline in both the intervention and control groups. Actual protein intake in the intervention groups ranged from 0.7 to 1.1 g/kg/day. One study noted malnutrition in the LPD group. We found no data on the effects of LPDs on health-related quality of life and costs.

AUTHORS' CONCLUSIONS

The results show that reducing protein intake appears to slightly slow progression to renal failure but not statistically significantly so. However, questions concerning the level of protein intake and compliance remain. Further longer-term research on large representative groups of patients with both type 1 and type 2 diabetes mellitus is necessary. Because of the variability amongst patients, there might perhaps be a six month therapeutic trial of protein restriction in all individuals, with continuation only in those who responded best. Trials are required of different types of protein.

Low protein diets for chronic kidney disease in non diabetic adults

BACKGROUND

For more than fifty years, low protein diets have been proposed to patients with kidney failure. However, the effects of these diets in preventing severe renal failure and the need for maintenance dialysis have not been resolved.

OBJECTIVES

To determine the efficacy of low protein diets in delaying the need to start maintenance dialysis.

SEARCH STRATEGY

Cochrane Renal Group trials register, the Cochrane Central Register of Controlled Trials, MEDLINE, and EMBASE. Congress abstracts (American Society of Nephrology since 1990, European Dialysis Transplant Association since 1985, International Society of Nephrology since 1987). Direct contacts with investigators. Date of most recent search: December 2004.

SELECTION CRITERIA

Randomised trials comparing two different levels of protein intake in adult patients suffering from moderate to severe renal failure, followed for at least one year.

DATA COLLECTION AND ANALYSIS

Two reviewers independently selected studies and extracted data. Statistical analyses were performed using the random effects model and the results expressed as relative risk (RR) for dichotomous outcomes with 95% confidence intervals (CI). Collection of the number of "renal deaths" defined as the need for starting dialysis, the death of a patient or a kidney transplant during the trial.

MAIN RESULTS

Eight trials were identified from over 40 studies. A total of 1524 patients were analysed, 763 had received reduced protein intake and 761 a higher protein intake. Two hundred and fifty one renal deaths were recorded, 103 in the low protein diet and 148 in the higher protein diet group (RR 0.69, 95% CI 0.56 to 0.86, P = 0.0007). To avoid one renal death, 2 to 56 patients need to be treated with a low protein diet during one year.

AUTHORS' CONCLUSIONS

Reducing protein intake in patients with chronic kidney disease reduces the occurrence of renal death by 31% as compared with higher or unrestricted protein intake. The optimal level of protein intake cannot be confirmed from these studies.

Dietary protein restriction as a treatment for slowing chronic kidney disease progression: The case against (Review Article)

Low-protein diets (<or=0.7 g/kg per day) have been advocated for over 70 years as a means of slowing the rate of progression of kidney disease and delaying the appearance of uraemic symptoms and need for dialysis. However, the available evidence to date suggests that the benefit : risk ratio of dietary protein restriction is not favourable in that: (i) compliance is generally sub-optimal; (ii) most of the published randomised controlled trials demonstrate that low-protein diets do not significantly slow the rate of kidney disease progression; (iii) meta-analyses of controlled trials have demonstrated strong evidence of publication bias favouring studies with positive, rather than negative, results; (iv) the optimal level and duration of dietary protein intake have not been defined; (v) there is no convincing clinical evidence that dietary protein restriction provides any benefit beyond that afforded by angiotensin blockade; and (vi) low-protein diets are associated with both statistically and clinically significant declines in nutritional markers in chronic kidney disease populations, which already have a high prevalence of malnutrition. Patients with progressive kidney disease are therefore likely to be better served by avoiding dietary protein restriction (thereby ensuring optimal preservation of their nutrition) and instituting alternative, proven renoprotective measures (e.g. renin-angiotensin system blockade, blood pressure reduction and statin therapy).

Severe dietary protein restriction in overt diabetic nephropathy: benefits or risks?

OBJECTIVE

To evaluate whether restricting protein intake may delay the progression of chronic renal failure caused by overt diabetic nephropathy and also whether this increases the risk of malnutrition.

DESIGN

Prospective clinical trial.

SETTING

Nephrology outpatients.

PATIENTS

Sixty-nine patients (32 affected by type 1 and 37 by type 2 diabetes, all treated with insulin) affected by both overt diabetic nephropathy and hypertension.

INTERVENTION

The study was started once hypertension and glycemia had been under control for at least 3 months. Two groups of patients, matched for similar mean glomerular filtration rate value and nutritional status, were studied: a low-protein diet (0.6 g/kg/d) was randomly prescribed to 35 patients, whereas in the other 34 patients a free diet intake was maintained for 12 months.

MAIN OUTCOME MEASURE

Renal function and nutritional status.

RESULTS

The protein intake was significantly different in the 2 groups of patients, whereas the average decline of glomerular filtration rate during the follow-up was comparable. In the low-protein diet group, serum prealbumin concentration significantly decreased after 9 months, whereas serum albumin decreased at the end of the study.

CONCLUSION

Severe dietary protein restriction does not seem to delay the progression of renal disease in patients with overt diabetic nephropathy, whereas it may induce malnutrition.

Nutritional support in chronic renal failure: systematic review

BACKGROUND AND AIMS

The purpose of this systematic review was to locate and assess in patients with chronic renal disease the quality of scientific evidence to establish graded recommendations based on the efficacy and effectiveness of nutritional support.

METHODS

Computerized and online versions of MEDLINE (from 1989 through March 1999) and EMBASE (from 1988 through January 1999) were consulted. The Cochrane Library and the online Healthstar (from 1975) databases were also searched for clinical trials. A total of 593 studies were assessed. Following methodological review (primary reviewer), only 45 studies reviewed met criteria for selection and were analyzed by a group of experts (secondary reviewer). A final consensus was reached between the co-ordinators, experts and methodologists.

RESULTS AND CONCLUSIONS

Low and very low-protein diets associated with specific enteral supplements are indicated in most patients with chronic renal disease and in patients with incipient diabetic nephropathy to slow progression of disease and to improve their overall status, contributing to improved survival (grade A recommendation). The use of protein-restricted diets in diabetic nephropathy is only indicated in type I diabetes mellitus (grade A recommendation). An improvement in nutritional parameters was found when specific diets were given in chronic renal disease (grade C recommendation).

Protein restriction for diabetic renal disease

OBJECTIVES

To determine whether protein restriction slows or prevents progression of diabetic nephropathy towards renal failure.

SEARCH STRATEGY

Computerised databases MEDLINE (1976-1996) and EMBASE (1974-1996) were searched using keywords diabetes mellitus, diabetic nephropathy, dietary proteins, diet, protein restricted and uremia. Recent issues of selected journals (Diabetic Medicine, Diabetologia, Diabetes Care, Kidney International, Nephrology Dialysis and Transplantation) were handsearched for papers not yet in the computerised databases. Reference lists of papers were also checked.

SELECTION CRITERIA

This review was not limited to randomised controlled trials. All trials involving people with insulin-dependent diabetes following a lower protein diet for at least 4 months were considered since the straight line nature of progression as reflected by GFR means that patients can act as their own controls in a before and after comparison.

DATA COLLECTION AND ANALYSIS

Data were extracted for length of follow up, level of protein restriction, renal function and dietary compliance. No studies of the impact of protein restriction on outcomes such as the need for dialysis or transplantation were found. The trials reported only the effect on short-term indicators such as creatinine clearance.

MAIN RESULTS

Overall a protein restricted diet (0.3-0. 8g/kg) does appear to slow the progression of diabetic nephropathy towards renal failure.

REVIEWER'S CONCLUSIONS

The results show that reducing protein intake appears to slow progression to renal failure, but some questions remain unanswered. The first is what level of protein restriction we should be used? The trials aimed for a daily intake of between 0.3 to 0.8g/kg of protein. The second concerns compliance in routine care - what level would be acceptable to patients? The third concerns long term outcomes -the present trials use proxy indicators such as creatinine clearance rather than outcomes such as time to dialysis or prevention of ESRF. All trials were carried out in subjects with insulin-dependent diabetes. It remains to be seen if a lower protein intake would slow the progression of nephropathy affecting the non-insulin dependent diabetic population.

Analysis of factors influencing chronic renal failure progression

One of the most important characteristics of chronic renal failure (CRF) is its progression to end stage renal disease. CRF progression depends of many factors indicated in numerous experimental and clinical studies. The present study was undertaken with the aim to examine the role of sex, etiology of CRF, renal function at the beginning of the study, hypertension and protein intake on CRF progression. Ninety-two patients (47 female and 45 male) aged between 17 and 70, with various underlying kidney diseases and various degrees of CRF were followed for 8 years. CRF progression was expressed as Creatinine clearance (CCr) and reciprocal values of serum Creatinine (SCr) against time. CRF progression was slower in women than in men, but not significantly. Patients with diabetic nephropathy (b = 0.00006) and glomerulonephritis (b = 0.00005) had faster progression of CRF than patients with nephrosclerosis (b = 0.00002), tubulointerstitial nephritis (b = 0.00003) and polycystic kidney disease (b = 0.00003). The fastest progression of CRF was in patients with the lowest SCr values at the beginning of the study. Proper regulation of blood pressure was the most important factor in slowing down CRF progression, independently of kind of antihypertensive drugs. Neither angiotensin converting enzyme inhibitors (b = -0.00001) nor calcium channel blockers (b = -0.00002) showed better effects on CRF progression slowing down in comparison with other antihypertensive drugs (b = -0.00001). Low protein diet slowed down CRF progression, but not significantly. In conclusion, our retrospective study confirms that CRF progression depends on sex, underlying renal diseases and serum Creatinine levels at the beginning of the study. Good regulation of blood pressure and low protein diet can slow down CRF progression.

Diabetic nephropathy and pregnancy

Knowledge of the pathogenic mechanisms of diabetic nephropathy (by which hyperglycemia, hyperfiltration, and hypertension cause the gradual development of microproteinuria, mesangial expansion, and eventual glomerular closure) provides the basis for effective treatment. Intensified glycemic control and antihypertensive therapy that is safe for the fetus are crucial for success during pregnancy. Considered outcome measures include perinatal survival, size at birth, child development, and long-term maternal renal function.

Controlled low protein diets in chronic renal insufficiency: meta-analysis

OBJECTIVE

To determine whether low protein diets retard the development of end stage renal disease.

DESIGN

Meta-analysis of 46 trials since 1975, from which six randomised controlled trials were selected.

SETTING

Five trials in Europe and one in Australia between 1982 and 1991.

SUBJECTS

890 patients with mild to severe chronic renal failure who were followed up for at least one year. 450 patients received a low protein diet and 440 a control diet.

INTERVENTION

Difference in protein intake between control and treated groups of at least 0.2 g protein/kg/day.

MAIN OUTCOME MEASURE

Number of renal deaths (the necessity to start dialysis or death of patient during study).

RESULTS

156 renal deaths were recorded, 61 in the low protein diet group and 95 in the control group, leading to an odds ratio of low protein to control of 0.54 with a 95% confidence interval of 0.37 to 0.79.

CONCLUSIONS

This result, obtained on a large population of patients suffering from chronic renal insufficiency, strongly supports the effectiveness of low protein diets in delaying the onset of end stage renal disease.