Chronic Kidney Disease: Nutritional Considerations

Managing CKD presents a nutritional challenge. Patients with CKD frequently have risk factors for atherosclerosis (hypertension, insulin resistance, and dyslipidemia), which would benefit from a fat-, sodium-, and sugar-restricted (but high-fiber) diet. But these patients also commonly present with malnutrition,³ which calls for a less restricted meal plan. The right kind of diet, as described below, can help control blood pressure, cholesterol, and the buildup of nitrogenous waste products in the blood, and may prevent cardiovascular events. Dietary changes can also slow progression to end-stage kidney disease. The following dietary factors may be clinically important.

Low Total and Animal Protein

A prolonged high-protein intake is accompanied by an increase in GFR,⁴ which in turn may cause intraglomerular hypertension and eventual loss of renal function.⁵ In women with mild renal insufficiency, those with the highest protein intake had a 3.5-fold risk for developing a ≥15% decrease in GFR, compared with those eating the least protein. This effect was attributed to nondairy animal (not vegetable) sources of protein.⁵

Evidence for the benefit of a low-protein diet is not conclusive. Some studies suggest that restricting protein intake to 0.6-0.75 g/kg/day may help delay the need for renal replacement therapy.^6,7 The Modification of Diet in Renal Disease (MDRD) study did not reveal significant benefit. However, a later meta-analysis of five studies (including the MDRD Study A) reported a roughly 35% lower risk for renal failure or death on a low-protein diet⁸. A more recent review based on eight trials and including a total of 1524 patients indicated that, although the optimal protein intake remains unknown, reducing protein intake in individuals with CKD (and without diabetes) may reduce mortality from this disease by 31%, compared with higher or unrestricted protein intake.⁹

In patients with severely limited renal function, very low-protein diets (0.3 g vegetable protein/kg/day) supplemented with essential amino acids and keto analogs can correct metabolic acidosis, secondary hyperparathyroidism, resistance to insulin, and decreased Na(+)-K(+)-ATPase activity.¹⁰ Animal products are also a major source of cholesterol-raising saturated fat; avoiding animal products helps reduce elevated cholesterol levels (see below).

Sodium Restriction

Patients with CKD are often salt-sensitive, responding to elevated intakes of sodium chloride with increases in glomerular filtration and proteinuria.¹¹ Blood pressure is a known determinant of CKD progression, and sodium restriction is an important part of blood pressure control in kidney disease.¹² Although additional clinical trials are required, evidence indicates that patients with chronic renal failure who adhere to low-salt diets have half the rate of decline in GFR as those who follow high-sodium diets.¹³

Water-Soluble Vitamins

Low-protein diets may increase the risk for deficiency of thiamine, riboflavin, and especially pyridoxine, and vitamin C levels are also often low in CKD patients. In CKD patients not on dialysis, 5 mg per day of pyridoxine and 30 to 50 mg per day of vitamin C have been suggested.¹⁴ No standard recommendations for amounts of thiamine or riboflavin exist for this group of patients.

Vitamin D Supplementation

Deficiency of vitamin D is present early in the course of CKD, and correction may prevent activation of key pathogenic mechanisms in cardiovascular disease (eg, inflammation, myocardial cell hypertrophy and proliferation, and the renin-angiotensin system).¹⁵

A Diet High in Fiber and Low in Saturated Fat and Cholesterol

Most patients with chronic kidney disease die from cardiovascular causes before developing end-stage renal disease.¹⁶ In a significant number of patients, pharmacologic (ie, statin) reduction of serum lipids preserves GFR and reduces proteinuria.¹⁷ Studies show that a vegetarian diet has similar effects on lipids and decreases proteinuria.^18,19

Dietary and supplemental sources of fiber may be helpful for reducing the buildup of nitrogenous waste products in the blood that cause many symptoms of uremia. Fiber may act through several mechanisms, including the adsorption and excretion of metabolic wastes and stimulation of colonic bacterial proliferation and subsequent incorporation of excess nitrogenous compounds.²⁰ Although further clinical trials are needed, preliminary data indicate that high-fiber diets²¹ and fiber-supplemented diets²² both cause fecal nitrogen loss. Decreases in serum urea equal to 17% and 19% after 8 and 12 weeks of fiber supplementation, respectively, have been found with certain types of fiber, such as ispaghula husk.²²

A High-Calorie Diet

Protein-calorie malnutrition in CKD may result from loss of appetite and poor food intake. In turn, these may be caused by uremia, unpalatable therapeutic diets, lack of adequate dialysis, psychosocial or economic factors, and leptin-induced anorexia and metabolic acidosis.¹⁴ Malnutrition-related consequences of metabolic acidosis include proteolysis; negative nitrogen balance; impairments of insulin activity, glucose utilization, and albumin synthesis; and a reduction in insulin-like growth factors (eg, IGF-1).¹⁴ Protein-energy deficit is associated with poor clinical outcome and mortality in chronic kidney disease, and the low albumin concentration that is a marker for this condition is a strong predictor of death in this population. Nutritional assessment is essential in these patients.

Omega-3 fatty acid supplements. Omega-3 fatty acid supplements are under study for their role in a form of primary glomerulonephritis called immunoglobulin A nephropathy. Some results have been encouraging, at least for some patient subgroups.²⁶ Nevertheless, more study is required before omega-3 fatty acids can be considered an effective treatment for IgA nephropathy.

Orders

Diet: Low protein (0.3-0.6 g/kg ideal body weight, and dependent on residual kidney function); low-sodium, high-fiber, low saturated fat and cholesterol.

Nutrition Consultation: Registered dietitian to determine appropriate energy and protein requirements.

Exercise prescription.

Smoking cessation.

What to Tell the Family

CKD increases the risk for both cardiovascular events and end-stage disease that requires dialysis. The control of high blood pressure through sodium restriction and medication is central to preventing the progression of CKD. However, the addition of other dietary changes (restricting total and animal protein intake, and following a high-fiber diet) may help by reducing urea, cholesterol, and blood glucose levels. Lifestyle changes such as quitting smoking and getting regular exercise may improve disease management.