Diet and Nutrition Goals: Chronic kidney disease (CKD)

PACE Hospitals

Chronic kidney disease (CKD) risk and progression may be related to genetic factors especially in younger people but nutritional factors also play an important role. Diabetes and hypertension together account for majority of cases of CKD. Both diabetes and hypertension are closely linked with nutrition and largely preventable. Strong adherence to western dietary habits is associated with increased risk of CKD. More than 90% of cases of diabetes and 65% of hypertension cases can be prevented if adhered to healthy life style and diet.

The working unit of kidney is nephron which contains a tuft of capillaries surrounded by a capsule that captures fluid filtered in the glomerulus. This filtrate passes down through the tubules which reabsorb fluid, electrolytes and other substances and ultimately urine is produced. The function of kidneys is reflected by the GFR, which is defined as the amount of blood filtered of some substance per unit time. The total GFR is sum of each nephron GFR. In two kidneys average number of nephrons are 2 million. When nephron number is high each nephron need not work at maximum capacity, so normal kidney function can be maintained even after substantial nephron loss (like in people who donate kidney). Not all people are born with high number of nephrons and they are at risk of kidney disease. As age increases nephrons drop out and this drop out is increased by diabetes and hypertension. So, the remaining nephrons have to work more to maintain GFR. The requirement to work at a higher capacity leaves the nephron vulnerable to the potential deleterious effects of high intake of red meat, animal fat, highly processed foods preserved with phosphate and sodium and low intake of fresh fruits and vegetables.

For a patient with CKD who is not on dialysis, dietary changes are effective and low-cost intervention for CKD progression prevention. When CKD is first diagnosed importance of diet should be explained to patient as this is the best time when interventions are likely to act. We will focus on three important dietary factors in relation to CKD- animal protein, salt and fruit and vegetable intake.

Protein

When people with reduced nephron number take high amount of animal protein it may lead to further nephron loss. After meat meal both renal blood flow and GFR increases. This increase in blood flow is limited to animal protein intake compared to vegetarian diet. Amino acids from protein causes dilatation of blood vessels which supply to nephron units. Imagine nephron as a water balloon, if pressure inside it increases it bursts. In the same way inside nephron because of increased blood flow tension in the walls of nephron increases. This stretching of the walls inside the nephron will lead to scarring of the nephrons. High amount of animal protein intake can also damage cells (podocytes) which act as barrier for leakage of albumin in the nephron.

Red meat, cheese and egg yolk contain choline, phosphatidylcholine, and L-carnitine. They are converted by bacteria in gut into uremic toxins called trimethylamine N-oxide (TMAO) and p-cresyl sulfate. These uremic toxins are excreted by the kidney, and in the setting of reduced kidney function, circulating levels may increase and contribute to atherosclerosis and further worsening of kidney function.

Phosphate

Protein sources contain phosphate. In plant sources of protein, phosphorus is in the form of phytic acid which cannot be digested easily in humans so phosphorus absorption is low. Whereas animal protein and preserved foods with inorganic phosphate has high absorption of phosphorus. High intake of phosphorus in patients with CKD can harm the kidney and can also lead to deposition of calcium in kidney and blood vessels.

Salt (sodium chloride)

High salt intake has many deleterious effects. It can increase blood pressure and worsen the CKD. It also has effect on heart. High salt intake increases blood volume and increases blood pressure and negate the effects of anti-hypertensive medications. It makes management of blood pressure difficult in patients with kidney disease. Reduction in salt intake results in lower blood pressure and also lower urine albumin excretion. Low salt intake benefits are more in patients who are of old age, advanced CKD and in obese patients. Patients with chronic kidney disease should avoid processed foods and take meals prepared with less salt.

Fruits and vegetables

Acid is produced in the body during metabolism. To buffer this acid bicarbonate is used up in the body. Excess acid is excreted and bicarbonate is regenerated in the kidney. The amount of acid produced in the body depends on the type of food we take. The acid load is increased when we take meat in the diet. So, in patients who already have CKD the remaining nephrons which are over working have to work even more to excrete the excess acid which is formed. This leads to damage to tubules in the kidney. High acid load by itself also can directly damage the kidney tubules. Diets high in fruits and vegetables and low in animal protein are associated with lower acid load and thus lower workload for each individual nephron.Increasing alkali intake with fruits and vegetables or with sodium bicarbonate tablets may lower net endogenous acid excretion by more than one-third which may decrease individual nephron workload and slow loss of kidney function.

Fibre

High intake of fibre is associated with reduced cardiovascular risk and reduced mortality in patients with CKD. Fibre intake is important in patients with advanced CKD or kidney failure. With advanced CKD there are high levels of urea in the blood which can damage the gut barrier and allow the passage of gut bacteria into blood which can cause damage to body. High fibre in diet will increase the level of good bacteria (Bifidobacterium) which strengthens the gut barrier. High fibre diet also prevents constipation and helps in excretion of urea and potassium in the stool.