Forty-six studies (n=7,476) were included. There were 20 studies (n=6,192) in 17 publications of nutritional support in CRF patients in pre-dialysis, 7 studies (n=1,004) in CRF patients in haemodialysis, and 19 studies (n=280) in patients with insulin-dependent diabetes.
One systematic review, 3 meta-analyses, 25 randomised controlled trials and 14 other study designs were included in the review.
Effects of nutritional therapy on the progression of renal function in 'general population' CRF.
Ten of the 13 studies concluded that protein- and phosphate-restricted diets slowed deterioration of renal function, retarded the rate of fall of glomerular filtration rate and delayed the onset of end-stage renal failure (deferring the patient's entry into a dialysis programme).
Effects of nutritional therapy on nutritional status in 'general population' CRF.
Six studies performing anthropometric measurements concluded that protein restriction, both in low-protein and very low-protein diets associated with specific enteral supplements, allowed weight and lean body muscle mass (mid-arm circumference) to be maintained or even improved. Six studies also concluded that with both types of diets, albumin levels were maintained and transferrin and cholesterol levels were lowered.
Effects of nutritional therapy on the progression of renal function in diabetic patients.
Fifteen studies concluded that protein-restricted diets reduced nocturnal microalbuminuria and delayed the onset or progression of nephropathy. This effect was noticeably greater in hyperfiltrating patients. The benefit in these patients appeared to be independent of glycaemic control. The beneficial effect of diet was evident even before the onset of nephropathy.
Effects of nutritional therapy on nutritional status in diabetic patients.
All 19 studies confirmed good metabolic tolerance to protein restriction, with a reduction in hyperglycaemia and decreased insulin requirements (in some cases, due partly to an undesirable reduction in caloric intake). The majority of the studies confirmed that anthropometric parameters (weight, mid-arm circumference and triceps skinfold) were preserved. No change or a slight improvement was seen in albumin, triglyceride and cholesterol levels. Some studies confirmed the beneficial effect of these diets in lowering urinary losses of albumin and immunoglobulin G.
Effects of nutritional support on patients with CRF in dialysis (energy supplements).
Energy supplements improved weight in 2 cohort studies; the amino acid profile was also improved in one of these studies, although there was no demonstrable nutritional benefit. In one cohort study, supplementation with a high-calorie, low-phosphate diet containing 0.6 g of protein was well-tolerated.
Effects of nutritional support on patients with CRF in dialysis (low-calorie, low-protein, liquid diet as a supplement).
One cohort study of a very low-protein diet supplemented with essential amino acids and ketoacids found it to be associated with malnutrition in 50% of the patients. One small trial compared two low-phosphate, high-calcium liquid diets providing 1.25 g protein and 35 kcal/kg per day to a control diet with a higher phosphate content, concluded that enteral products as sole sources of nutrition were well-tolerated by patients in haemodialysis and that preparations specifically designed for these patients have advantages over standard preparations. Two other studies looked at the benefit of protein-restricted diets to defer initiation of dialysis: one pointed out a slower deterioration of renal function; the other confirmed delayed initiation of dialysis, with a subsequent beneficial effect on mortality.
Effects of nutritional support on patients with CRF in dialysis (disease progression).
Supplemented very low-protein diets appeared to be useful in the pre-dialysis phase to slow the progression of end-stage renal failure, and in one study they reduced mortality during the first 2 years of dialysis treatment. When these diets were tested for their ability to reduce dialysis to once per week, it was found that although urea levels were maintained, there was a loss in clearance capacity and above all, a deterioration of nutritional status.
Effects of nutritional support on patients with CRF in dialysis (nutritional effects).
Both energy supplements and the different diets tested allowed weight to be maintained. Very low-protein diets caused a worsening of the anthropometric parameters studied. Supplementation with a calorically dense, low-phosphate liquid diet providing 0.6 g protein improved weight and triceps skinfold thickness. The study comparing 3 diets, which contained 1.25 g protein and 35 kcal/kg per day, found that they were well-tolerated and that compliance was adequate. Albumin and pre-albumin levels were maintained. An increase in triglycerides and a decrease in cholesterol was seen. The low-phosphate diets allowed good control of plasma phosphorus and an improvement in calcium metabolism, avoiding the need to administer phosphorus binders and thus reducing constipation.