Effect of restricting dietary protein on the progression of renal failure in patients with insulin-dependent diabetes mellitus

Role of Glycemic Control and Protein Restriction in Clinical Management of Diabetic Kidney Disease

OBJECTIVE

To assess the role of control of blood glucose levels and restriction of dietary protein in the management of diabetic nephropathy.

METHODS

We summarize the results of pertinent published studies of glycemic control and modification of protein intake to provide information about strategies that potentially could benefit patients with diabetes and renal dysfunction.

RESULTS

Considerable evidence is available to support the contention that improved glycemic control may have beneficial effects on the development and progression of diabetic renal disease. Maximal benefits of improved glycemia occur when instituted before the onset of macroalbuminuria. Once overt diabetic nephropathy is established, improved glycemic control may not be beneficial. Current evidence indicates that a glycosylated hemoglobin level of less than 8.1% should be the glycemic goal. At this level, the risk of developing micro-albuminuria is substantially reduced, and the risk of hypoglycemia is minimized. Most studies have been conducted in type I diabetes, and the results have been extrapolated to type II diabetes. Whether improved glycemic control will be equally beneficial in the nephropathy of type II diabetes has yet to be determined. Although some scientific evidence supports dietary protein restriction in patients with diabetic nephropathy, the extent of restriction needed for optimal benefits and minimal side effects remains to be determined. On the basis of current information, patients with both types of diabetes who have evidence of nephropathy should have protein limited to the recommended dietary allowance for adults (0.8 g/kg of body weight per day or approximately 10% of total daily caloric intake), and protein should be derived primarily from vegetable and lean animal sources.

CONCLUSION

End-stage renal disease is not inevitable in patients with diabetic nephropathy. Normalization of glucose levels and modification of protein intake can favorably influence the course of diabetes-related kidney disease.

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.

Preventing complications in diabetes mellitus: the role of the primary care physician

Many Americans, knowingly or unknowingly, are afflicted with diabetes. Because of a lack of awareness or a disbelief that aggressive treatment benefits patients on the part of both patients and physicians, diabetes, particularly NIDDM, remains underdiagnosed and undertreated despite complications that can dramatically diminish quality of life. Increasing evidence that good glycemic control forestalls if not prevents these outcomes makes it the primary care physician's imperative to diagnose diabetes before complications develop. Physicians, through targeted screening and aggressive treatment of patients in whom they diagnose this chronic disease, can markedly reduce diabetes-related morbidity and mortality.

Diabetic nephropathy in type II diabetes

The incidence of end-stage renal failure in patients with type II diabetes has dramatically increased in recent years, both in the United States and, with some delay, in some European countries. These epidemiologic observations have thoroughly dispelled the mistaken belief that renal prognosis was benign in type II diabetes. Recent interest has focused on the early stages of nephropathy in type II diabetes. With respect to renal hemodynamics, renal morphology, and progression of established diabetic nephropathy, there are no substantial differences between types I and type II diabetes. There is good evidence that preventive measures are effective, ie, glycemic control, blood pressure control, protein restriction, and discontinuation of smoking. The high prevalence of the disease (which in principle is preventable) calls for intense efforts to (1) educate the medical community, (2) substantially improve patient education and medical care, and (3) intensify research in this field.

Effects of dietary protein restriction on regional amino acid metabolism in insulin-dependent diabetes mellitus

We studied subjects with insulin-dependent diabetes mellitus (IDDM) and controls by administering primed continuous infusions of L-[1-13C,15N)]leucine and L-[2,3-13C2]alanine to measure whole body and forearm metabolism of these amino acids during ample protein intake and again after 4 wk of moderately restricted protein intake. Decreased rates of whole body protein degradation, leucine transamination, leucine oxidation, and increased forearm alanine release produced by dietary protein restriction occurred equivalently in IDDM subjects under short-term tightly managed glycemia and in controls. Dietary protein restriction did not affect whole body alanine appearance or forearm leucine appearance, disposal, or balance in IDDM subjects or controls. IDDM subjects differed from controls only in that normal forearm leucine balance was maintained at higher rates of leucine appearance and disposal. We conclude that IDDM subjects adapt normally to dietary protein restriction. Undernutrition during moderate protein deprivation in these patients likely occurs during episodes of poor glycemic control.

Diabetes mellitus and associated hypertension, vascular disease, and nephropathy. An update

Because considerable important information has been published since our previous review, this update concentrates on new findings with regard to cardiovascular and renal risk factors contributing to the striking morbidity and mortality of these coexisting diseases. For example, a large body of investigative data has recently emerged suggesting or delineating a pathogenic role for hyperglycemic-related glycosylation and oxidation of lipoproteins and vascular and renal tissues. Great strides have recently been made in the understanding of platelet, coagulation, lipoprotein, and endothelial abnormalities in the pathogenesis of cardiovascular and renal disease associated with diabetes mellitus and hypertension. Major progress has been made in clarifying the pathophysiology of glomerulosclerosis and other processes involved in the progression of diabetic nephropathy. Furthermore, accumulating data surveyed in this review address new and promising pharmacological interventions that specifically address these pathophysiological mechanisms.

Taking control of diabetes

Management has changed dramatically: There is no doubt now that strict glycemic control protects against nephropathy, neuropathy, and retinopathy. Direct evidence comes from study of intensive insulin therapy in IDDM. The implication is that similar protection can be gained in NIDDM. Microalbuminuria mandates ACE inhibition and dietary protein restriction. Proliferative retinopathy can be arrested with laser photocoagulation.

Low-protein diets in the treatment of chronic renal failure

Dietary protein restriction is an established method of preventing the symptoms of uremia but three questions should be asked before beginning this type of therapy: Will the diet maintain adequate nutrition? Can compliance be monitored? Will the low-protein diet prevent uremic symptoms and change the course of the disease? There are positive answers to these questions. Recently it has been shown that the metabolic acidosis associated with kidney failure causes catabolism by increasing the degradation of muscle protein and of essential amino acids. The mechanism for these responses includes increased mRNAs encoding enzymes involved in catabolic pathways. Activation of these pathways would impair the ability of patients to respond to a low-protein diet because the ability to reduce the oxidation of essential amino acids and degradation of protein would be limited.

L-arginine may mediate the therapeutic effects of low protein diets

We have previously shown beneficial effects of dietary protein restriction on transforming growth factor beta (TGF-beta) expression and glomerular matrix accumulation in experimental glomerulonephritis. We hypothesized that these effects result from restriction of dietary L-arginine intake. Arginine is a precursor for three pathways, the products of which are involved in tissue injury and repair: nitric oxide, an effector molecule in inflammatory and immunological tissue injury; polyamines, which are required for DNA synthesis and cell growth; and proline, which is required for collagen production. Rats were fed six isocaloric diets differing in L-arginine and/or total protein content, starting immediately after induction of glomerulonephritis by injection of an antibody reactive to glomerular mesangial cells. Mesangial cell lysis and monocyte/macrophage infiltration did not differ with diet. However, restriction of dietary L-arginine intake, even when total protein intake was normal, resulted in decreased proteinuria, decreased expression of TGF-beta 1 mRNA and TGF-beta 1 protein, and decreased production and deposition of matrix components. L-Arginine, but not D-arginine, supplementation to low protein diets reversed these effects. These results implicate arginine as a key component in the beneficial effects of low protein diet.

Cholesterol-lowering therapy may retard the progression of diabetic nephropathy

There is experimental evidence to suggest that hypercholesterolaemia may play a pathogenetic role in progressive glomerular injury. We investigated the effect of cholesterol-lowering therapy on the progression of diabetic nephropathy in 34 patients with non-insulin-dependent diabetes mellitus. Patients were randomly assigned in a single-blind fashion to treatment with either lovastatin, an HMG CoA reductase inhibitor (n = 16; mean dose 30.0 +/- 12.6 mg/day) or placebo (n = 18) for 2 years. Renal function was assessed by serially measuring the serum creatinine, glomerular filtration rate (using Cr51-EDTA), and 24-h urinary protein excretion. Lovastatin treatment was associated with significant reductions in total cholesterol (p < 0.001), LDL-cholesterol (p < 0.001) and apo B (p < 0.01), the reductions at 24 months being 26, 30 and 18%, respectively. Beneficial effects on serum triglyceride, HDL-cholesterol and apo A1 levels were also observed. Lp(a) showed no significant change in both groups. Glomerular filtration rate deteriorated significantly in the placebo group after 24 months (p < 0.025) but showed no significant change in the lovastatin-treated patients. The increase in serum creatinine was statistically significant (p < 0.02) in placebo-treated patients at 12 and 24 months, and in the lovastatin group after 24 months. Twenty-four hour urinary protein excretion increased in both groups (p < 0.05). Lovastatin treatment was not associated with significant elevations in liver or muscle enzymes. We conclude that effective normalisation of hypercholesterolaemia may retard the progression of diabetic nephropathy.

Effect of intensive treatment on diabetic nephropathy in patients with type I diabetes

We evaluated the long-term effect of an intensive treatment of diabetic nephropathy (anti-hypertensive drugs, low protein diet, multiple insulin injections to achieve a good metabolic control) on glomerular filtration rate (GFR) and albumin excretion rate (AER). Fourteen type I diabetic patients (mean age 45 +/- 9.5 years, mean duration of diabetes 23.5 +/- 7.3 years, 8 males/6 females) with glomerular filtration rate < 70 ml/min-1/1.73 m2 and albumin excretion rate > 30 micrograms/min were treated intensively for 36 months. This intensive treatment consisted of multiple insulin injections, antihypertensive therapy with ACE inhibitors and a low-protein diet (0.8 g/kg body wt/day.) Renal function was evaluated as GFR and AER. HbA1c mean value decreased significantly from 8.7 +/- 0.8% to 6.5 +/- 0.5% (P < 0.0002). GFR rose from 58 +/- 12 ml/min-1/1.73 m2 to 84 +/- 11 ml/min-1/1.73 m2 (P < 0.0008). AER decreased from 208 micrograms/min (range: 73 to 500) to 63.8 micrograms/min (range 15 to 180; P < 0.05). Systolic and diastolic blood pressure decreased respectively from 144 +/- 26 mm Hg to 120 +/- 15 mm Hg and from 89 +/- 9 mm Hg to 75 +/- 8 mm Hg (P < 0.01). We obtained a rise of GFR and a reduction of proteinuria after three years of this treatment. We suggest that this intensive treatment in all patients with early stage diabetic nephropathy may be effective in slowing the progression to renal failure.

Remission of nephrotic range proteinuria in type I diabetes. Collaborative Study Group

The present study assessed the extent to which remission of nephrotic-range proteinuria occurred in patients with Type I diabetes enrolled in the Captopril Study, a placebo controlled multicenter clinical trial of captopril therapy in diabetic nephropathy. Of the 409 patients recruited into the Captopril Study, 108 had nephrotic-range proteinuria (> 3.5 g/24 hr) at entry in the Study (baseline). This group was the subject of the present study. Remission of nephrotic-range proteinuria was defined as follows: (1) Onset of the remission was taken as the date when proteinuria was first noted to be < or = 1.0 g/24 hr. (2) The reduction in proteinuria had to be sustained for a minimum of six months and until the end of the Captopril Study. (3) During the remission, the average of all 24 hour proteinuria measurements could not exceed 1.5 g. (4) Decline in renal function could not explain the reduced proteinuria. That is, the patient's serum creatinine during the entire period of observation in the Captopril Study had to remain at less than a doubling of the baseline serum creatinine. Remission of nephrotic-range proteinuria occurred in 7 of 42 patients assigned to captopril (16.7%, mean follow-up 3.4 +/- 0.8 years) and in 1 of 66 patients assigned to placebo (1.5%, mean follow-up 2.3 +/- 1.1 years; P = 0.005, comparing remission rate in captopril vs. placebo-treated patients).(ABSTRACT TRUNCATED AT 250 WORDS)

Therapeutic progress. III: Diabetic nephropathy

Diabetic nephropathy is a common cause of end stage renal failure. Patients ultimately require dialysis or transplantation and endure a poor quality of life in association with increased mortality. Due to the quantitative significance of this problem there is also a considerable financial burden. It has been generally accepted that once nephropathy is established it is irreversible although aggressive anti-hypertensive treatment can delay its progression. More recently there have been numerous reports proposing a specific renal protective role of certain drugs. In this article we review the current literature on the use of angiotensin converting enzyme inhibitors in diabetic nephropathy. There is strong evidence that the use of ACE inhibitors in diabetic nephropathy (in the presence or absence of hypertension) slows the progression of deterioration in renal function and may even arrest its progression if detected at the microproteinuric stage.

Current therapeutic management of diabetic nephropathy

Roughly 40% of all patients with insulin-dependent diabetes mellitus (IDDM) develop diabetic nephropathy with proteinuria, hypertension and a decrease in glomerular filtration rate 10 to 20 years after the onset of the disease, and 5 years later most patients suffer from end-stage renal disease. Microalbuminuria, defined as an urinary albumin excretion rate (UAER) between 30 and 300 mg/day, strongly predicts the development of nephropathy in IDDM. Nearly all patients with IDDM, a decreasing glomerular filtration rate and a UAER > 300 mg/day have coexisting hypertensive disease additionally worsening renal function. We review the results of recent long-term studies of the current therapeutic management in diabetic patients by means of better blood pressure control, low-protein diet and near-normal blood glucose control in the early microalbuminuric phase as well as in the later phases of the disease characterized by diabetic nephropathy with a UAER > 300 mg/day. Since the large majority of studies have been performed on IDDM, our conclusions with regard to therapy are only valid in this subgroup of diabetic patients.

Reduction of dietary protein and phosphorus in the Modification of Diet in Renal Disease Feasibility Study. The MDRD Study Group

OBJECTIVE AND DESIGN

The Modification of Diet in Renal Disease (MDRD) Feasibility Study was designed to test procedures and evaluate the feasibility of a full-scale clinical trial aimed at assessing the effects of reduction of dietary protein and phosphorus on progression of renal disease.

SETTING AND SUBJECTS

Ninety-six patients with chronic renal insufficiency were randomly assigned to different diets in one of two studies depending on their glomerular filtration rate.

INTERVENTION

The diets contained three different protein and phosphorus levels: moderate diet = 1.3 g protein per kilogram per day and 16 to 20 mg phosphorus per kilogram per day; low diet = 0.575 g protein per kilogram per day and 5 to 10 mg phosphorus per kilogram per day; and very low diet with keto or amino acids = 0.28 g protein per kilogram per day and 4 to 9 mg phosphorus per kilogram per day. Eight-five patients were monitored for at least 6 months; maximum follow-up was 22 months.

MAIN OUTCOME MEASURES

Compliance with study diets was measured monthly using urea nitrogen appearance and 3-day diet diaries plus one 24-hour recall. The main outcome measure was change or maintenance of glomerular filtration rate.

STATISTICAL ANALYSES PERFORMED

Data were analyzed by analysis of variance and paired t tests.

RESULTS

Mean dietary protein intake, as determined by urea nitrogen appearance, decreased significantly in participants assigned to the diets low and very low in protein and phosphorus (P < .05). Overall, the follow-up protein intake (based on urea nitrogen appearance) as a percentage of baseline ranged from 45.8% to 83.1%. Analysis of diet diaries showed better dietary adherence than indicated by urea nitrogen appearance. Review of the exchange methodology used in dietary instruction suggests that imprecision of the exchange lists may have been a factor in the difficulty study participants had in achieving +/- 10% of the target protein goal.

APPLICATIONS

Based on the MDRD Feasibility Study, the protocol for the full-scale study was modified to include protein counting instead of food exchange methodology to monitor protein intake.

Microalbuminuria: prognostic and therapeutic implications in diabetes mellitus

Thirty years following the development of the first radioimmunoassay for albumin, microalbuminuria is widely acknowledged as an important predictor of overt nephropathy in patients with Type 1 diabetes and of cardiovascular mortality in Type 2 diabetes. In addition, there is accumulating evidence to suggest that diabetic patients with microalbuminuria may have more advanced retinopathy, higher blood pressure, and worse dyslipidaemia than patients with normal albumin excretion rates. Recent studies have focused on the role of intervention, principally with antihypertensive therapy and intensive glycaemic control, in reducing microalbuminuria. While successful in reducing urinary albumin excretion it remains to be established whether such therapies will be translated into a reduction in renal failure and decreased cardiovascular morbidity and mortality.

Rates of progression to end stage renal failure in nephropathy secondary to type 1 and type 2 diabetes mellitus

BACKGROUND

Diabetic nephropathy is now the commonest single cause of end-stage renal failure (ESRF) in New Zealand.

AIMS

To investigate differences in the natural history of established nephropathy in Type 1 and 2 diabetes.

METHODS

Retrospective analysis of the rate of progression to ESRF in 17 subjects with Type 1 diabetes (predominantly European) compared to 29 subjects with Type 2 diabetes (all Polynesian). The rate of decline of renal function was determined from serial creatinine measurements (median 5, range 3-8) during progression of chronic renal failure to end stage. Glomerular filtration rate (GFR) was estimated from creatinine measurements using the Cockcroft Gault equation, and the regression slope of these measurements against time was used to determine rate of change of renal function.

RESULTS

GFR fell significantly more rapidly in the group with Type 2 diabetes than in those with Type 1 diabetes: median 1.7 (interquartile range 1.2 to 2.3) mL min-1 month-1 vs 1.1 (interquartile range 0.4 to 1.5) mL min-1 month-1, p = 0.017. During the study period the mean reduction in diastolic blood pressure in subjects with Type 1 diabetes (15 mmHg) was greater than that in the Type 2 subjects (8 mmHg), but the stage at which antihypertensives were commenced was similar in the two groups. Glycaemic control was worse in the subjects with Type 1 diabetes (p < 0.005). The differences in blood pressure control were not significant on analysis of covariance which indicated that ethnicity was the major determinant of the different rates of decline of GFR between the groups. We conclude that in subjects with diabetic nephropathy the rate of progression to ESRF is more rapid in Polynesians with Type 2 diabetes than in Europeans with Type 1 diabetes. This could contribute to the apparent excess of Type 2 diabetic subjects of Polynesian origin on renal replacement programmes in New Zealand.

Microalbuminuria: pathogenesis, prognosis and management

The development in recent years of sensitive assays specific for albumin has facilitated extensive investigation of the pathophysiology and clinical significance of microalbuminuria. It is now clear that the appearance of microalbuminuria represents a crucial event in the natural histories of diabetes mellitus and essential hypertension. It reflects the presence of generalized vascular damage and is strongly predictive of subsequent renal failure, cardiovascular morbidity, and death. Therapeutic interventions, including strict diabetic and blood-pressure control, can reduce microalbuminuria and improve the overall prognosis. The detection and treatment of microalbuminuria in these high-risk groups should now form an integral part of their management. Large-scale screening programmes are also recommended for insulin-dependent diabetics.

Low-protein diet regulates a proximal nephron insulin-like growth factor binding protein

Previous studies have demonstrated that the glomerulus and proximal tubule basolateral membrane possess both insulin-like growth factor (IGF) receptors and IGF-binding proteins (IGFBPs). The purpose of this study is to examine the control of these proteins in defined nephron segments during dietary protein restriction. Animals were fed isocaloric 6% (low-protein [LP]) or 40% (high-protein) protein diets for 7 to 10 days. 125I[IGF] affinity labeling of membranes prepared from isolated glomeruli or proximal tubule basolateral membranes demonstrated two proteins on autoradiograms of 6% polyacrylamide gels with molecular weights of 140,000 d and more than 200,000 d that were blocked by 300 nmol/L unlabeled IGF-I. The lower molecular weight species has been identified previously as the alpha subunit of the IGF-I receptor and was upregulated by a 6% LP diet. The upregulation of the IGF-I receptor was evident on 12% polyacrylamide gels of both glomeruli and basolateral membranes. Another protein with a molecular weight of approximately 38,000 d also was upregulated by LP diet. The protein was evident on 125I-IGF-I ligand blots and was immunostained with IGFBP-5 antibodies. Cytosol prepared from cortical tissue also demonstrated a 31,000-d protein that was immunostained with IGFBP-5 antibodies in animals fed a LP diet, but not in animals fed a high-protein or normal diet. RNA prepared from cortical tissue and hybridized with a IGFBP-5 cDNA probe revealed a 6.0-Kb transcript that was increase by LP diet.(ABSTRACT TRUNCATED AT 250 WORDS)

Combined pancreas and kidney transplantation normalizes protein metabolism in insulin-dependent diabetic-uremic patients

In order to assess the combined and separate effects of pancreas and kidney transplant on whole-body protein metabolism, 9 insulin-dependent diabetic-uremic patients (IDDUP), 14 patients after combined kidney-pancreas transplantation (KP-Tx), and 6 insulin-dependent diabetic patients with isolated kidney transplant (K-Tx), were studied in the basal postabsorptive state and during euglycemic hyperinsulinemia (study 1). [1-14C]Leucine infusion and indirect calorimetry were utilized to assess leucine metabolism. The subjects were studied again with a combined infusion of insulin and amino acids, given to mimic postprandial amino acid levels (study 2). In the basal state, IDDUP demonstrated with respect to normal subjects (CON): (a) higher free-insulin concentration (17.8 +/- 2.8 vs. 6.8 +/- 1.1 microU/ml, P < 0.01) (107 +/- 17 vs. 41 +/- 7 pM); (b) reduced plasma leucine (92 +/- 9 vs. 124 +/- 2 microM, P < 0.05), branched chain amino acids (BCAA) (297 +/- 34 vs. 416 +/- 10 microM, P < 0.05), endogenous leucine flux (ELF) (28.7 +/- 0.8 vs. 39.5 +/- 0.7 mumol.m-2.min-1, P < 0.01) and nonoxidative leucine disposal (NOLD) (20.7 +/- 0.2 vs. 32.0 +/- 0.7 mumol.m-2. min-1, P < 0.01); (c) similar leucine oxidation (LO) (8.0 +/- 0.1 vs. 7.5 +/- 0.1 mumol.m-2.min-1; P = NS). Both KP-Tx and K-Tx patients showed a complete normalization of plasma leucine (116 +/- 5 and 107 +/- 9 microM), ELF (38.1 +/- 0.1 and 38.5 +/- 0.9 mumol.m-2.min-1), and NOLD (28.3 +/- 0.6 and 31.0 +/- 1.3 mumol.m-2.min-1) (P = NS vs, CON). During hyperinsulinemia (study 1), IDDUP showed a defective decrease of leucine (42% vs. 53%; P < 0.05), BCAA (38% vs. 47%, P < 0.05), ELF (28% vs. 33%, P < 0.05), and LO (0% vs. 32%, P < 0.05) with respect to CON. Isolated kidney transplant reverted the defective inhibition of ELF (34%, P = NS vs. CON) of IDDUP, but not the inhibition of LO (18%, P < 0.05 vs. CON) by insulin. Combined kidney and pancreas transplanation normalized all kinetic parameters of insulin-mediated protein turnover. During combined hyperinsulinemia and hyperaminoacidemia (study 2), IDDUP showed a defective stimulation of NOLD (27.9 +/- 0.7 vs. 36.1 +/- 0.8 mumol.m-2.min-1, P < 0.01 compared to CON), which was normalized by transplantation (44.3 +/- 0.8 mumol.m-2.min-1).

Effects of dietary protein restriction on glucose and insulin metabolism in normal and diabetic humans

We determined whether the amount of protein in the diet can affect insulin requirements in subjects with diabetes mellitus and glucose metabolism in normal subjects. Seven normal-weight volunteers with uncomplicated, intensively controlled, type I (insulin-dependent) diabetes and 12 similar nondiabetic subjects were studied on a metabolic ward before and after consuming a maintenance-energy but protein-free diet for 10 days. Blood glucose levels of diabetic subjects were measured seven times daily in response to insulin administration by continuous subcutaneous infusion. The plasma glucose appearance rate (Ra) was measured in seven normal subjects and all diabetic subjects using a primed-continuous infusion of D-[6,6-2H2]glucose. After adaptation to the protein-restricted diet, diabetic subjects experienced a 30% decrease in average preprandial and average daily blood glucose concentrations (P < .01); this occurred despite a concurrent 25% decrease in both basal and bolus insulin dosages (P < .001). Protein restriction decreased the postabsorptive glucose Ra (P < .05) and insulin concentrations (P < .01) of normal subjects by 20%, and increased their fasting glucagon concentrations by 24% (P < .01). We conclude that severe protein restriction decreases insulin requirements in type I diabetes and fasting hepatic glucose output and basal insulin levels in normal subjects. This effect appears to be mediated in part by decreased hepatic gluconeogenesis, but a contributory influence of increased insulin sensitivity is not ruled out.

Adaptive responses to very low protein diets: the first comparison of ketoacids to essential amino acids

Eight patients with chronic renal failure (GFR 18.8 +/- 2.7 ml/min) were randomized to a crossover comparison of a very low protein diet (VLPD) containing 0.28 g protein and 35 kcal per kg per day, plus an isosmolar mixture of either ketoacids (KA) or essential amino acids (EAA). Subjects initiated the diets 14 days before hospital admission and following a four-day equilibration, a five-day nitrogen balance (BN) was performed. Whole-body protein turnover (WBPT) was measured during fasting and feeding using intravenous [1-13C]leucine and intragastric [5,5,5-2H3]leucine. Even though the VLPD/KA regimen contained 15% less nitrogen, BN was neutral and did not differ between the regimens. Nitrogen conservation with KA was due to a reduction in urea nitrogen appearance. Rates of WBPT measured during fasting and feeding did not differ between the KA or EAA regimens. During both regimens, feeding decreased protein degradation, whereas protein synthesis was unchanged. Although feeding stimulated leucine oxidation, rates were 50 to 100% lower than reported in CRF patients consuming 0.6 or 1.0 g protein/kg/day. Thus, neutral Bn with the VLPD regimen is achieved by a marked reduction in amino acid oxidation and a postprandial inhibition of protein degradation.

Blood pressure, diet and the progression of nephropathy in patients with type 1 diabetes and hypertension

To examine the relationships between the normal dietary intakes of protein and phosphate, blood pressure, and the progression of diabetic nephropathy, we prospectively studied 20 Type 1 diabetic subjects of mean age 43 +/- 10 years (SD) with early nephropathy (mean serum creatinine 115 +/- 43 mumol l-1) over 1 year. Three-monthly measurements of blood pressure, glycaemic control, and normal dietary intake (3-day weighed food records) and 6-monthly measurements of glomerular filtration rate (using a single injection of chromium 51-EDTA) were made. GFR changed at a median rate of -0.89 ml min-1 1.73 m-2 month-1 (range +0.85 to -2.55 ml min-1 1.73 m-2 month-1). Mean dietary protein intake (1.22 g kg-1; range 0.78 to 1.55 g kg-1) and phosphate intake (21.5 mg kg-1; range 14.1 to 30.4 mg kg-1) were not significantly related to the rate of change in GFR. Only mean systolic blood pressure was significantly related to change in GFR, and accounted for 45% of the variability in GFR decline in the 18 subjects who completed the study (r = 0.67; R2 = 0.449; F1,16 = 13.2; p < 0.005; 95% confidence interval for r: 0.336-0.867). A mean systolic blood pressure of 140 mmHg or below was associated with no significant decline in GFR over a median period of 13 months.(ABSTRACT TRUNCATED AT 250 WORDS)

Higher levels of microproteinuria in Asian compared with European patients with diabetes mellitus and their relationship to dietary protein intake and diabetic complications

Asian patients with diabetes have a higher prevalence of renal disease than their European counterparts. The aim of the study was to investigate the pattern of the renal excretion of proteins in 70 Asian and 70 European patients with diabetes and to relate it to dietary intake of protein and prevalence of diabetic complications. Compared with matched Europeans, Asian patients had an increased urinary excretion of albumin and transferrin (p < 0.02) with 14 Asians and 6 Europeans having significant microalbuminuria (> 30 micrograms min-1). In 12 Asians and all 6 Europeans this was associated with complications from diabetes, particularly vascular. Asian patients had significantly more ischaemic heart disease (p < 0.001) but less neuropathy (p < 0.001) and retinopathy (p < 0.05) than their matched European counterparts. Asian diets were lower in protein (median (range) Asian vs European: 12.5% (6-29%) vs 19% (11-27%); p < 0.01) and carbohydrate but higher in fat than European diets. There was no correlation between dietary protein intake and excretion of any of the urinary proteins measured. However, a significant correlation was found in Asians between protein intake and length of residence in the UK (p < 0.005). Unless ways to reduce complications can be found then future allocation of resources will need to take this into consideration in areas with large Asian communities.

Are the nutritional recommendations for insulin-dependent diabetic patients being achieved?

Dietary intake was assessed, using a 3-day recorded food diary, in 122 patients with insulin-dependent diabetes. Subjects were selected randomly from patients attending a diabetic clinic and stratified for age, sex, and duration of diabetes. The findings were compared to the dietary recommendations of the European Association for the Study of Diabetes (EASD) and to the findings in a recent Irish National Nutrition Survey. The average daily protein intake among diabetic patients was 18% of the total calories, significantly higher than recommended by EASD and significantly higher than in the age-matched general population. Dietary fat intake was on average 37% of total calorie intake, again significantly higher than recommended and greater than in the general population among older patients. Saturated fat intake was higher than recommended and polyunsaturated fat intake was low. The average carbohydrate intake was 42% of total calories, significantly lower than recommended and similar to that in the general population. Sugar intake was lower and starch intake was higher among patients than in the general population, however. Fibre intake was also lower than recommended, but was higher than in the general population. We conclude that the present dietary targets for diabetic patients are not being fully achieved.

The quantitative relationship between treated blood pressure and progression of diabetic renal disease

Antihypertensive therapy reduces the rate at which glomerular filtration rate (GFR) declines (delta GFR) in diabetic nephropathy; however, the optimal blood pressure is unknown. The quantitative relationship between treated blood pressure and delta GFR was analyzed retrospectively in 59 patients with established diabetic nephropathy and treated hypertension using weighted univariate and weighted multivariate regression. The GFR was calculated using the Cockcroft and Gault formula. More rapid GFR loss correlated most strongly with higher diastolic blood pressures (r = 0.70; P < 0.0001); for each millimeter of mercury of diastolic blood pressure, the GFR decreased by 0.69 mL/min/yr. This relationship remained present if those individuals with diastolic pressures greater than 90 mm Hg were eliminated from the study (r = 0.50; P < 0.001). The correlation for systolic blood pressure was weaker (r = 0.30; P < 0.05) and explained completely by covariance between systolic and diastolic blood pressures. The correlation for mean blood pressure (r = 0.59; P < 0.0001) fell between the correlations for diastolic and systolic blood pressures. Proteinuria, serum albumin concentration, and serum cholesterol concentration also correlated with delta GFR. In multivariate analysis, neither these indices of disease severity nor the initial GFR explained the correlation between delta GFR and diastolic blood pressure. Age, sex, race, type of diabetes, and percentage of glycosylated hemoglobin did not correlate with delta GFR.

Recruitment experience in the full-scale phase of the Modification of Diet in Renal Disease Study

The Modification of Diet in Renal Disease (MDRD) Study is a randomized, multicenter clinical trial testing the effects of three different levels of dietary protein and phosphorus intake and two levels of blood pressure control on the rate of loss of kidney function in persons with various chronic kidney diseases. During a 27-month recruitment period, 2507 persons who had objective evidence of impaired kidney function were screened at 15 centers. Eight hundred and forty men and women aged 18-70 with a glomerular filtration rate between 13 and 55 ml/min/1.73 m2 were randomized. Medical record review was the primary means of identifying study participants at the beginning of recruitment. Later, use of mass media was instrumental in alerting both the public and the medical community of the need for MDRD Study participants. Overall, the most important sources of randomized participants were referral by personal physician (45.4%) and relative/friend (5.6%), and self-referral after hearing about the trial from newspapers (23.9%) and television (5.2%). Review of medical records from defined patient populations was the source of 22.3% of the randomized study participants. A total of 9.4% of the randomized participants called a toll-free (800) telephone number before contacting the centers.

Protein intake and glomerular hyperfiltration in insulin--treated diabetics without manifest nephropathy

Protein intake in relation to glomerular filtration rate (GFR) and urinary albumin excretion (UAE) has been studied in 96 insulin-treated diabetic patients, 20-40 years of age and without nephropathy. They had diastolic blood pressure (DBP) not exceeding 90 mmHg and a GFR exceeding -2 SD of the age-related value. They were without medications except for insulin. There were no significant differences in protein intake between diabetic patients with and without hyperfiltration (1.18 +/- 0.26 g/kg/d vs 1.21 +/- 0.42 g/kg/d, p = 0.75) or between diabetic patients with or without increased UAE (1.16 +/- 0.41 g/kg/d vs 1.24 +/- 0.37 g/kg/d, p = 0.37). No relations were found between protein intake and GFR or UAE in the whole sample, but a positive relation was found between UAE and protein intake in patients with increased UAE. Protein intake correlated with UAE in hyperfiltrators who use tobacco (n = 8, r = 0.85, p = 0.01), but not in non-users (n = 11, r = 0.24, p = 0.48). In conclusion our findings give no support for a relation between high protein intake and glomerular hyperfiltration in insulin-treated-diabetic patients. However, in contrast to non-users of tobacco, a positive relation was found between UAE and protein intake in tobacco users with hyperfiltration.

The course of kidney function in type 2 (non-insulin-dependent) diabetic patients with diabetic nephropathy

We evaluated the impact of some putative progression promoters on kidney function in albuminuric Type 2 (non-insulin-dependent) diabetic patients with biopsy-proven diabetic glomerulosclerosis. Twenty-six patients (1 female) with a mean age of 52 (standard error 2) years and a known mean duration of diabetes of 9 (1) years were followed-up prospectively for a mean of 5.2 (range 1.0-7.0) years. Twenty-one patients received antihypertensive treatment. During the observation period the glomerular filtration rate decreased from 83 (24-146) to 58 (2-145) ml.min-1 x 1.73 m-2 (mean (range)) (p < 0.001). The mean rate of decline in glomerular filtration rate was 5.7 (-3.5 to 22.0) ml/min per year. Albuminuria increased from 1.2 (0.3-7.2) to 2.3 (0.4-8.0) g/24 h (geometric mean (range)) (p < 0.001). Arterial blood pressure remained unchanged: 162/93 (SE 4/3) and 161/89 (4/2) mm Hg. Univariate analysis showed the rate of decline in glomerular filtration rate to correlate with systolic blood pressure (r = 0.71, p < 0.001), mean blood pressure (r = 0.56, p < 0.005), albuminuria (r = 0.58, p < 0.005) and the initial glomerular filtration rate (r = -0.49, p < 0.02). The rate of decline in glomerular filtration rate did not correlate significantly with dietary protein intake, total cholesterol, high-density lipoprotein cholesterol or HbA1c. Three patients died from uraemia and four patients died from cardiovascular disease. Two patients required renal replacement therapy at the end of the observation period. Our prospective observational study revealed that one-fifth of the patients developed end-stage renal failure during the 5-year observation period.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of protein intake on glycaemic control and renal function in type 2 (non-insulin-dependent) diabetes mellitus

Recent clinical investigations have suggested that dietary protein intake may modulate the progression of diabetic nephropathy and influence glycaemic control in Type 2 (non-insulin-dependent) diabetes mellitus. Twelve normotensive Type 2 diabetic patients with microalbuminuria took part in a randomized cross-over trial of a 3-week high protein diet (2.0 g/kg.desirable weight per day) and a 3-week moderate protein diet (0.8 g/kg desirable weight per day) to test the simultaneous effect of protein intake modulation on glycaemic control and renal function. Both diets were isoenergetic and the moderate protein diet was supplemented with calcium and phosphate. Renal function and glycaemic control were evaluated at the beginning and at the end of each diet. The moderate protein diet reduced the urinary albumin excretion rate, glomerular filtration rate, creatinine clearance, and proteinuria without adversely affecting glycaemic control; fasting glycaemia and the ratio of fructosamine to proteins were significantly reduced. The high protein diet induced similar improvements in glycaemic control but small changes in renal function.

Detection and management of early diabetic nephropathy

It has proven difficult to alter the progression of diabetic nephropathy once overt proteinuria is established. The presence of microalbuminuria reflects an early renal lesion that may be more amenable to therapeutic intervention. Dietary protein restriction, improved glycemic control, and aggressive treatment of high blood pressure all have shown beneficial effects in some patients. Angiotensin-converting enzyme inhibitor therapy may offer specific advantages in terms of its renal protective effects.

Diabetic nephropathy

Diabetic nephropathy occurs in approximately 35% of all diabetic patients, both insulin and non-insulin dependent. It accounts for the largest proportion increase of all diseases as a cause for endstage renal disease in the United States. Certain populations, i.e., Pima Indians and Mexican and black Americans, have a higher propensity for developing diabetic nephropathy. The reasons for this increased incidence, however, are unclear. Pathophysiologically, numerous changes in vascular reactivity and renal physiology occur in early diabetes. These include increased sodium avidity, lower threshold for vasoconstriction secondary to angiotensin II and norepinephrine, a greater than 50% of normal increase in renal vasodilation following a protein meal, and loss of renal autoregulation. These differences are not seen in nondiabetic hypertensive subjects. The therapeutic approach to lower elevated arterial pressure in these patients should take these changes in physiology into account. Specifically, antihypertensive agents are preferred that have natriuretic properties and also blunt the effects of vasoconstrictors on both the vasculature and the cellular level, i.e., inhibit mesangial hypertrophy and matrix expansion, the hallmark of diabetes. Ideal agents, therefore, are angiotensin converting enzyme (ACE) inhibitors in the early stages of the disease, and certain calcium antagonists once renal insufficiency occurs. These choices are largely due to the hemodynamic, natriuretic, and anti-proteinuric effects of these agents. Good blood pressure control is essential for preservation of renal function, regardless of agents used. The ACE inhibitors and calcium antagonists of the verapamil and diltiazem groups have demonstrated superior efficacy for preservation of renal function over conventional therapy.

Diet as culprit or therapy. Stone disease, chronic renal failure, and nephrotic syndrome

A number of renal disorders are amenable to dietary manipulation. This article reviews nutritional strategies for the management of renal stone disease, chronic renal failure, and nephrotic syndrome. The first portion discusses dietary factors that promote urolithiasis and dietary recommendations utilized in the medical management of stone disease. The second segment discusses the pathophysiology of the progression of renal disease and nutritional interventions to delay progression. Finally, the third portion examines losses of protein, vitamins, and minerals in the nephrotic syndrome and makes recommendations for replacement.

Monitoring diabetic nephropathy: glomerular filtration rate and abnormal albuminuria in diabetic renal disease--reproducibility, progression, and efficacy of antihypertensive intervention

The principal end point in the evaluation of treatment in incipient and overt diabetic nephropathy is rate of decline in glomerular filtration rate (GFR). Therefore, information on reproducibility of GFR measurements is essential in the planning and evaluation of clinical trials. We studied reproducibility of GFR measurements in insulin-dependent and non-insulin-dependent diabetes mellitus patients using, respectively, a constant-infusion technique with urine collection and labeled iothalamate as a tracer marker and a single-shot procedure using Cr-EDTA, measuring the GFR from the decline in plasma level after bolus injection. The coefficient of variance in the insulin-dependent patients was from 7.5% to 8.8% with repeated measurements. In longitudinal studies with several measurements the mean coefficient of variances varied between 7.4% and 3.4%. In the non-insulin-dependent patients the coefficient of variances between two tests were 7.0% and 5.3% for normoalbuminuric and microalbuminuric patients, respectively. In cross-sectional studies as well as in longitudinal studies, it has been consistently shown that GFR is well preserved and at a supranormal level in patients with normoalbuminuria and microalbuminuria. A decline in GFR appears to start around the transition from microalbuminuria to overt diabetic renal disease, although more detailed studies are needed to support this finding. With regard to intervention trials, several studies document that microalbuminuria can be reduced by effective antihypertensive treatment, particularly with angiotensin-converting enzyme inhibitors, also in patients with normal or close to normal blood pressure. Preliminary results from long-term studies suggest that reduction in microalbuminuria in these patients is associated with preservation of GFR and, thus, apparently renoprotection. In patients with overt renal disease, it has been consistently shown that antihypertensive treatment reduces albuminuria as well as the rate of decline in GFR. This is also observed with combined treatment regimens, for instance beta blockers or angiotensin-converting enzyme inhibitors combined with diuretics, or the three types of drugs in combination.