Protein restriction in chronic renal failure

Fermentable carbohydrate and digestive nitrogen excretion

BACKGROUND

Interventions that restrict protein intake lower plasma urea concentration and may slow the progression of renal failure. The question arises whether the effect of a dietary protein restriction could be reinforced by enrichment of the diet with fermentable carbohydrate because these carbohydrates may stimulate the extra-renal route of nitrogen (N) excretion through the digestive route.

METHODS

The influence of fermentable carbohydrate and moderate protein restriction on N metabolism was investigated in a rat model of renal failure with ablation of 70% of renal mass compared with control rats with intact kidneys. Animals were adapted to diets varying with respect to nondigestible fermentable carbohydrate (0% or 10% fructooligosaccharide [FOS]) and with respect to protein content (10% or 18% casein).

RESULTS

Feeding FOS led to a considerable enlargement of the cecum (increase in contents, wall thickness, and blood flow). These changes resulted in a concomitant enhancement of urea N uptake into the cecum and a decrease in plasma urea concentration (-30%). The extent of urea uptake by the cecum was influenced by plasma urea level that was determined by the dietary protein level and by the renal function. Thus, compared with control rats, the rate of urea uptake by the cecum and the total N excreted by the uremic rats was greater under all nutritional conditions. It is noteworthy that, when expressed as a percentage of total N excretion, fecal N excretion nearly doubled in rats adapted to the low-protein diets containing FOS. These effects occurred in both control rats and in uremic rats, in which a 22% decrease in urinary N was recorded as a result of FOS in addition to the low-protein diet. Globally, decreasing the amount of protein in the diet and adding a fermentable carbohydrate led to a decrease in urinary N excretion of more than 65% in uremic rats.

CONCLUSION

These results suggest a possible usefulness for combining fermentable carbohydrate, such as FOS, with a low-protein diet to increase N excretion through the digestive route in detriment of the renal route. This may represent an efficient preventive measure to relieve the renal function in case of renal failure.

Effects of captopril treatment versus placebo on renal function in type 2 diabetic patients with microalbuminuria: a long-term study

We evaluated the renal effect of long-term antihypertensive treatment (12 months) with the angiotensin-converting enzyme inhibitor captopril compared to placebo in 15 type 2 diabetic patients with microalbuminuria. The patients were randomly allocated to captopril (n = 9) or placebo (n = 6). After 1-year therapy no significant decrease in blood pressure was demonstrated with captopril (139 +/- 17/80 +/- 9 versus 138 +/- 13/76 +/- 6 mmHg) or placebo (138 +/- 9/75 +/- 6 versus 135 +/- 14/79 +/- 10 mmHg). Only in a small hypertensive subgroup (n = 4) treated with captopril did we find a significant reduction in blood pressure (154 +/- 2/88 +/- 1 versus 142 +/- 7/78 +/- 5 mmHg, P < 0.05). The urinary albumin excretion rate did not change significantly either in the captopril group (95.6 mg/24 h, 25th percentile 138.4, 75th percentile 25.1; versus 127.8 mg/24 h, 25th percentile 29.3, 75th percentile 222) or in the placebo group (99.2 mg/24 h, 25th percentile 58.5, 75th percentile 125.8; versus 120.9 mg/24 h, 25th percentile 62.1, 75th percentile 179.7). There were also no alterations in renal blood flow or filtration rate. In the hypertensive subgroup treated with captopril a reduction in urinary albumin excretion rate after 3 and 6 months of treatment was observed (captopril 73.4 versus 24 and 41 mg/24 h, P < 0.05), but not after 12 months. Triglyceride and cholesterol levels remained constant before and after treatment while glycosylated hemoglobin decreased significantly after 12 months captopril (7.8 +/- 0.9 versus 6.9 +/- 0.7 mg%, P < 0.03).(ABSTRACT TRUNCATED AT 250 WORDS)

Restriction of dietary protein and progression of renal failure in diabetic nephropathy

In a study of the effect of a low-protein diet on the progression of renal disease 19 insulin-dependent diabetic patients with persistent clinical proteinuria were observed for 12-39 (mean 29) months while they were on a normal-protein diet (1.13 [0.06] g/kg per day), then for 12-49 (mean 33) months on a low-protein diet (0.67 [0.03] g/kg per day). The low-protein diet had no adverse effect on nutrition or glycosylated haemoglobin concentration. Mean supine blood pressure (BP) fell slightly on the low-protein diet and was probably due to the start or modification of antihypertensive medication in 9 patients. The mean rate of decline in glomerular filtration rate fell from 0.61 (SEM 0.14) ml/min per month with the normal-protein diet to 0.14 (0.08) with the low-protein diet, and this effect remained highly significant after adjustment for blood pressure, energy intake, and glycosylated haemoglobin. The rise in the fractional clearance of albumin during a normal-protein diet stopped with the low-protein diet, and there was a significant fall in albumin excretion from 467 (95% CI 234-895) micrograms/24 h on the normal-protein to 340 (138-719) on the low-protein diet. Thus, a low-protein diet, with its reduction in protein and possibly other dietary components such as phosphate or fat, seems to retard the rate of decline of glomerular filtration rate in diabetic nephropathy independently of blood pressure changes and glycaemic control.

Implementation of low-protein diets for treatment of persons with early diabetic nephropathy

Low-protein diets are being increasingly used as a treatment for early nephropathy associated with diabetes. Recent research studies have shown a decrease in proteinuria while serum albumin levels and weight have been maintained. A level of 0.6 g protein/kg ideal body weight has been suggested. In structuring these diets, fat should be restricted to approximately 30% of calories, with the remainder supplied as carbohydrate calories after the protein content has been calculated. In some persons, simple sugars need to be included to avoid excessive amounts of high-bulk, high-fiber carbohydrate foods. Insulin and oral agent dosages may need adjustment to compensate for increased glucose levels. Self-monitoring of glucose levels can provide valuable feedback for medication adjustment. Intensive dietary education is needed with these patients, as the diet is sometimes radically different from diets previously used. A hypothetical patient is described and diet calculations provided using the ADA Exchange Lists with accompanying menus.

Protein-induced glomerular hyperfiltration: role of hormonal factors

High protein diets acutely elevate the glomerular filtration rate. To characterize this response we administered 1 g of protein/kg body weight as a beef steak meal to nine, healthy male subjects and measured glomerular filtration rate (inulin clearance), renal plasma flow (p-amino hippurate clearance), plasma renin activity, aldosterone and plasma and urinary catecholamines. The subjects ingested the meal on three separate days and were pretreated with either placebo, 50 mg indomethacin (to inhibit renal prostaglandin synthesis), or 10 mg enalapril (to inhibit angiotensin II synthesis). Following placebo treatment protein feeding significantly increased the glomerular filtration rate, from a pre-meal level of 101 +/- 7 ml/min/1.73 m2 to a post-meal level of 130 +/- 6 ml/min/1.73 m2, P less than 0.005. A parallel rise in renal plasma flow and a fall in renal vascular resistance were noted. Indomethacin pretreatment attenuated the increase in glomerular filtration rate following the protein meal, 105 +/- 6 ml/min/1.73 m2 pre-meal level to 118 +/- 4 ml/min/1.73 m2 post-meal, P greater than 0.1. Enalapril pretreatment had no significant effect on protein-induced glomerular hyperfiltration. Protein feeding following placebo increased plasma aldosterone concentration while the concentrations were unchanged in the studies where enalapril or indomethacin was administered. Protein feeding following placebo or indomethacin did not alter plasma renin activity while plasma renin activity rose following enalapril administration. Urinary norepinephrine excretion rose while plasma norepinephrine concentration was unchanged in all three study groups. A decrease in urinary dopamine excretion was also noted four hours after the protein meal was ingested.(ABSTRACT TRUNCATED AT 250 WORDS)

Chronic renal failure after nephrotoxic nephritis in rats: contributions to progression

In rats dietary protein restriction decreases the rate of progressive glomerulosclerosis and the development of renal failure after subtotal nephrectomies. The present experiments were designed to see whether dietary protein had similar effects on renal failure after nephrotoxic nephritis (NTN). Groups of rats were fed isocaloric diets containing 8%, 18% and 78% casein. Irrespective of whether the diets were introduced 7 days or 30 days after induction of nephritis by a single injection of rabbit anti-rat nephrotoxic globulin, rats on 8% casein and 78% casein had significantly lower plasma creatinines than rats fed with 18% casein. Semiquantitative scoring systems were used to assess glomerular sclerosis, tubular atrophy and tubular calcification. Rats on 8% protein had significantly lower glomerular sclerosis scores than the other two groups. Tubular atrophy scores were similar in rats on 8% and 78% casein and significantly lower than those of rats on 18% casein. All rats on 8% and 18% casein diets had tubular calcification whereas rats on 78% casein did not. This suggested that the normal relation between glomerular sclerosis and tubular atrophy after NTN was altered by a 78% casein diet. This was confirmed by the slopes of the regression equation for glomerular sclerosis on tubular atrophy (0.54 +/- 0.07) for rats on 78% casein compared to the slopes of the regression equations for the other two groups which were 1.12 +/- 0.10 and 1.00 +/- 0.12, respectively. This difference is highly significant statistically, P less than 0.1 X 10(-5) (one-way analysis of variance). These results show that dietary protein has a variable effect on the development of renal failure after nephrotoxic nephritis.(ABSTRACT TRUNCATED AT 250 WORDS)

Is chronic renal transplant rejection a non-immunological phenomenon?

Five patients with chronic renal transplant rejection were subjected to dietary protein restriction (0.6 g/kg ideal body weight daily) with no change in immunosuppressive therapy. In all five patients the slope of the curve of reciprocal serum creatinine and time decreased (mean -46.0 +/- 11.8 before diet fell to -11.7 +/- 9.4; p less than 0.01). These findings support the hypothesis that non-immune mechanisms are dominant is chronic renal transplant failure.

Effects of aging on the renal glomerulus

The biologic price of aging includes progressive deterioration of renal function and structure. After the age of 30, glomerular filtration and renal blood flow rates decline in a linear fashion, so that values in octagenarians are only half to two thirds those measured in young adults. Renal mass similarly declines, and the incidence of sclerotic glomeruli increases with advancing age. Accordingly, the aging kidney is at high risk of eventual failure when functioning nephron number is further reduced by acquired renal disease. Recent evidence suggests that limitation of dietary protein intake delays the development of age- and disease-related glomerular sclerosis in experimental animals, and that dietary protein restriction may postpone end-stage renal disease in patients with progressive renal insufficiency.

Regional variations in British alcohol morbidity rates: a myth uncovered? I: Clinical surveys

Officially recorded rates of many alcohol related problems are much higher in the north than in the south of Britain. To try to shed some light on this the pattern and threshold for use of psychiatric and medical hospital services for alcohol dependence, abuse, and psychosis were studied in three areas differing greatly in official rates of alcohol related problems--namely, the Highland and Tayside regions in Scotland and part of the South East Thames region in England. The disparity in psychiatric admissions for alcohol dependence, abuse, and psychosis were found to be largely explained by admission policies which reflected geographical factors. The results of this study did not support the conventional view that rates of treated morbidity due to alcohol are appreciably higher in the north.

Selective effect of low protein diets in chronic renal diseases

It has recently been established that the rate of progression of chronic renal failure in man can be slowed by restricting dietary protein. Consequently, the short term and long term effects of a low protein diet on the course of different chronic nephropathies were studied in an attempt to delineate the factors that determine the response to such a diet. When a low protein diet was given for six months renal function improved significantly in nine patients with chronic tubulointerstitial nephritis (p less than 0.025); the diet had a marginally beneficial effect in 12 patients with chronic glomerulonephritis (p less than 0.05) and no effect in nine with hypertensive nephrosclerosis. The heterogeneous functional response in the patients with chronic glomerulonephritis correlated closely with the effect of the diet on these patients' proteinuria (r = 0.76, p less than 0.01). In a short term study (four weeks) of 12 patients with chronic renal failure changes in renal plasma flow were proportional to dietary protein intake. Renal vascular resistance fell during a high protein diet and increased when dietary protein was restricted. The changes in renal plasma flow during the low protein diet correlated well with the patients' long term functional response to the diet (r = 0.76, p less than 0.01). It is concluded that the response to a low protein diet in chronic renal failure is determined, firstly, by the nature of the underlying nephropathy, with maximal benefit being observed in non-glomerular disorders; secondly, by the effect of the diet on the proteinuria in chronic glomerulonephritis; and, thirdly, by the haemodynamic response to the diet, with patients with a reactive renal vascular bed improving with a low protein diet.