Renal Calculi and its Nutritional Management

Renal colic, the excruciating pain caused by a stone passing down the urinary tract is well known in all countries. The pain stops when the stone is passed naturally or removed by a surgeon. A patient may never have another attack or attacks may recur at irregular and sometimes long intervals. Most stones remain in the kidney where they often produce no symptom and are therefore known as SILENT STONES.

CHEMISTRY OF RENAL CALCULI:
Renal calculi are composed of different types of crystals; however, mostly renal stones are composed of Calcium Oxalate, Calcium Phosphate, Uric acid, Cystine, and Magnesium Ammonium Phosphate crystals.

TYPES OF STONES:

1) CALCIUM STONES: Most of the stones are generally composed of Calcium Oxalate and Calcium Phosphate crystals, but Calcium Oxalate stones are more common than Calcium Phosphate stones. The factors that promote the precipitation of Calcium Oxalate and Calcium Phosphate crystals in the urine are as follows:

  • Hypercalciuria: Hypercalciuria is defied as a daily urinary excretion of calcium above 300 mg in men and 250 mg in women. Hypercalciuria is further classified as Idiopathic and Secondary Hypercalciuria. In Idiopathic hypercalciuria, due to unknown reason there is increased intestinal absorption of calcium also there is decreased renal calcium reabsorption and there is increased bone resorption. Hyperparathyroidism, Sarcoidosis, excessive production of vitamin D, immobilization, medullary sponge kidneys, and excessive consumption of Calcium are some of the factors that are responsible for Secondary Hypercalciuria. Hypercalciuria is associated with an increased incidence of stone formation.
  • Hyperoxaluria: Refers to excess of Oxalate in urine. The greater part of the oxalate excreted in the urine is of endogenous origin and often comes from tissue metabolism of Glycine. Excessive intake of Vitamin C also causes hyperoxaluria. The commonest cause of hyperoxaluria is gastrointestinal malabsorption of dietary oxalates. Fatty acid malabsorption leads to calcium binding in the gut to produce calcium soaps of the fatty acids. This leaves the oxalate free and unbound to be absorbed. Enteric hyperoxaluria is exaggerated by a diet low in calcium.
  • Absence of stone forming inhibitors in urine: Substances which inhibit crystal growth are also present in urine. These include citrate, pyrophosphate, nephrocalin, and glycosaminoglycans. Absence of these inhibitors promotes stone formation.

2) URIC ACID STONES: About a quarter of patients with uric acid stones have hyperuricosuria with or without hyperuricemia & in most cases excessive dietary intake of Purine rich foods like liver , kidney sardines , brains etc causes hyperuricosuria . Uric acid is end product of Purine metabolism. Increased level of uric acid in urine causes decrease in pH of urine as a result urine becomes more acidic resulting in uric acid precipitation. Uric acid stones are also associated with acid/base metabolism disorders where the urine is excessively acidic.

3) CYSTINE STONES: Cystinuria is due to an inborn error of metabolism. The renal tubules fail to reabsorb the amino acids Cystine, Lysine, Arginine, and Ornithine. These pass in large amounts in urine where Cystine the least soluble amino acid tends to precipitate out and form stones.

4) STRUVITE STONES (Magnesium Ammonium Phosphate): Also known as infectious stones and triple phosphate stones are formed due to bacteria Proteus mirabilis (but also Klebsiella, Serratia, and Providencia species) which split urea to ammonia with the help of urease as a result of which urine pH becomes alkaline leading to stone formation.

5) XANTHINE STONES: Are composed of Xanthine. These stones are extremely uncommon and usually occur as a result of a rare genetic disorder.

NUTRITIONAL MANAGEMENT:

Depends upon the type of stone and conditions that are responsible for stone formation.

1)   Calcium Oxalate Stones: Particular emphasis should be directed at the calcium and oxalate content of the diet as an excess of both these nutrients has been associated with the formation of stones. If the stones formation is due to hypercalciuria, then a diet low in calcium should be taken. Also, a high fiber diet should be encouraged to reduce calcium absorption. Antacids containing calcium should be avoided. Protein and sodium intake should not be in excess as both increases urinary excretion of calcium.

If the stone formation is due to hyperoxaluria, then a diet high in calcium should be encouraged as calcium will form insoluble complexes with oxalic acid in gut and it will be excreted out of the body in the stools. Also, foods rich in Oxalic acid should be avoided.

  • Oxalic acid content of some foods:
  • Cereal / Bajra -21 mg / 100 gm
  • Pulse / Horse Gram 417 mg / 100 gm
  • Leafy Vegetables
    • Amaranth -772 mg / 100 gm
    • Spinach – 658 mg /100 gm
    • Rhubarb is also rich source of Oxalic acid
  • Other Vegetables – Drumsticks -101 mg /100 gm
  • Nuts / Almond – 407 mg / 100 gm
  • Fruits / Amla – 296 mg  /100 gm

Excessive intake of Vitamin C should be avoided as Vitamin C is metabolized and oxalic acid is formed. Fat malabsorption should be treated in order to prevent formation fatty acid and calcium soaps in intestine. Excessive intake of proteins and sodium should be prevented as both increases urinary excretion of calcium and in turn promotes calcium binding with oxalic acid in urine. The intake of water should be increased around 3000 ml of fluid should be taken daily. Stone inhibitors like citrates should be taken to prevent stone formation in urine.

2) Uric Acid Stones: Excessive intake of purine-rich foods like liver, brain, sardine, etc. should be avoided. Also, water consumption should be increased and alcohol intake restricted. Generally, an ALKALINE ASH DIET is recommended since it will help in reducing the acidity of urine by increasing the pH of urine.

An Alkaline Ash Diet consists mainly of fruits, vegetables, and milk with little meat, fish, eggs, cheese, and cereals that when catabolized leaves an alkaline residue to be excreted by urine. Alkaline Ash diet includes mostly all vegetables. Among fruits lemon, lime, watermelon, grape fruit, tomato, Avocado, etc.

3) Struvite Stones: In case of struvite stones, water should be taken in excess. Also, antibacterial medicines should be taken to destroy bacteria in urine and an ACID ASH DIET is recommended.

An Acid Ash Diet is a diet which mainly comprises of meat, fish, eggs, cereals, and consist of no or minimal amounts of fruits, vegetables, and milk. It gives acid residue to be excreted in urine when catabolized in the body. Acid Ash diet will make the urine acidic and there by prevents stones formation.

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