KIDNEY STONES & IT'S DIETARY 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 & sometimes long intervals. Most stones remain in the kidney where they often produce no symptom & 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 & Magnesium Ammonium Phosphate crystals.

TYPES OF STONES:

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

a) Hypercalciuria: Hypercalciuria is defied as a daily urinary excretion of calcium above 300 mg in men & 250 mg in women .Hypercalciuria is further classified as Idiopathic & Secondary Hypercalciuria. In Idiopathic hypercalciuria due to unknown reason there is increased intestinal absorption of calcium also there is decreased renal calcium reabsorption & there is increased bone resorption.
Hyperparathyroidism, Sarcoidosis, excessive production of vitamin D, immobilization, medullary sponge kidneys & 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.

b) Hyperoxaluria: Refers to excess of Oxalate in urine .The greater part of the oxalate excreted in the urine is of endogenous origin & 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 & unbound to be absorbed. Enteric hyperoxaluria is exaggerated by a diet low in calcium.

C) Absence of stone forming inhibitors in urine: Substances which inhibit crystal growth are also present in urine. These include citrate, pyrophosphate, nephrocalin, glycosoaminoglycans. 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 & Ornithine. These pass in large amounts in urine, where Cystine the least soluble amino acid tends to precipitate out & form stones.

4) STRUVITE STONES (Magnesium Ammonium Phosphate): Also known as infectious stones & 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.

DIETARY MANAGEMENT:

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

1) Calcium Oxalate Stones :
Particular emphasis should be directed at the calcium & 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 than 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 & Sodium intake should not be in excess as both increases urinary excretion of calcium.

If the stone formation is due to hyperoxalicuria than a diet high in calcium should be encouraged as calcium will form insoluble complexes with oxalic acid in gut & 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

1) CEREAL – BAJRA -21mgs/100 gms

2) PULSE - HORSE GRAM – 417mgs / 100 gms

3) LEAFY VEGETABLES –AMARANTH -772 mgs / 100 gms
- SPINACH – 658 mgs / 100 gms
- RHUBARB –is also rich source of Oxalic acid

4) OTHER VEGETABLES - DRUMSTICKS -101mgs /100 gms

5) NUTS – ALMOND – 407 mgs / 100 gms

6) FRUITS – AMLA – 296 mgs /100 gms



Excessive intake of Vitamin C should be avoided as Vitamin C is metabolized & oxalic acid is formed. Fat mal absorption should be treated in order to prevent formation fatty acid & calcium soaps in intestine. Excessive intake of proteins & sodium should be prevented as both increases urinary excretion of calcium & 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 & alcohol intake should be 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 & milk with little meat , fish , eggs , cheese & 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 & an ACID ASH DIET is recommended.
An Acid Ash Diet is a diet which mainly comprises of meat, fish, eggs & cereals & consist of no or minimal amounts of fruits, vegetables & milk & it gives acid residue to be excreted in urine when catabolized in the body . Acid Ash diet will make the urine acidic & there by prevent stones formation