Consultant Dietician, Great Ormond Street Hospital, London.*
|Kidney stones (also known as renal calculi) are stones of varying sizes, which form inside the kidneys, ureter, urinary bladder or the urethra. The kidneys are situated at the back of the abdomen and their function is to remove waste products from the blood and from the body in the form of urine, which passes down a tube called a ureter into the bladder.
If the concentration of a particular mineral in the urine is too high, crystals form which sometimes become kidney stone. Most kidney stones are only the size of a grain of sand but some may be large enough to fill the collection sack leading out of the kidney.
Kidney stones tend to form when the level of a particular substance in the urine is too high. This can either happen because the body produces too much of a substance due to a medical condition or because the persons diet is too high in that particular mineral therefore producing a higher concentration in the urine. Alternatively if the urine is very concentrated a stone is most likely to be produced. This is why a stone is most likely to occur in hot weather or in people who do not drink much fluid.
Kidney stones are not very common in children but however these stones are being discovered now with increasing frequency amounting for upto one in each 1000 childhood admissions. These stones are in the kidney in two thirds of reported cases and in the ureter in the remaining cases. Although urinary stones are uncommon in children less than two years old, older children are at greater risk independent of age and sex.
Symptoms: Very often it is possible to have a kidney stone without it causing any symptoms at all especially if it is lying stationary within the kidney. They may be related to recurrent kidney infections. However if a stone passes down the ureter towards the bladder it generally causes a severe colicky pain in the back just above the ribs and follows the course of the stone. Once the stone reaches the bladder, the pain subsides. Stone blocking the flow of urine must be removed (surgically or through sound/shock waves). Microscopic hematuria (blood in urine) and abdominal pain are the presenting symptoms in majority of the cases.
Causes: Although primary hyperabsorption (increased absorption) of dietary calcium is the most commonly detected metabolic abnormality in children with urinary stones, other conditions including juvenile rheumatoid arthritis, inflammatory bowel disease, hyperparathyroidism, osteoporosis, gastrointestinal disorders and urinary tract infections carry enhanced risk for stone formation.
Types of stones: The types of minerals that create kidney stones vary. Many are made from calcium in people who have a very high calcium diet or who have a medical condition which causes them to have high levels of calcium in their blood, such as hyperparathyroidism. A substance called as oxalate can be found in some stones often in people who have a diet high in spinach, nuts, etc. Uric acid stones can occur as a result of gout or in certain metabolic disorders (where there is too much uric acid in the blood). A very rare component of kidney stones is a substance called cystine, which in some people can be leaked in high quantities into the urine.
Most stones contain
Calcium oxalate (60%)
Calcium phosphate (9%)
Or a combination of both (11%)
Less common stones are composed of
Struvite stones (also known as infectious stones)
Xanthine stones (rare*)
MODIFICATION OF DIET IN URINARY CALCULI
Calcium oxalate stones:
1 Fluid intake:
It should be increased to 3000ml/ day or more depending on the tolerance of the patient, since it helps to dilute urine to produce less concentration of the constituents of the stone. Liquids that could be consumed are fruit juices, barley water, coconut water, lime juice etc.
- Avoid a high protein diet.
- Calcium restriction: This may be restricted along with oxalate. Generally foods rich in calcium are rich in phosphorus with the exception of meat which contains less calcium but is very rich in phosphorus (table 1.1 & 1.2).
Oxalate restriction: All foods that contain large amounts of oxalates should be avoided if the stone is a calcium-
- oxalate stone (table 1.3).
- Avoid taking vitamin, mineral supplements.
- Avoid too much vitamin C and calcium containing antacids.
- Avoid vegetables and fruits containing seeds such as tomatoes, lady's finger, brinjal, capsicum, watermelon, guava etc.
Uric acid stones:
- Avoid purine rich foods.(Table 1.4)
- Increase fluid intake.
- Decrease animal protein.
Table 1.1 Foods rich in calcium
||Rich sources of
||Cereals such as ragi, whole bengal,
gram(chana), moth beans(matki),|
Rajmah, soyabeans, horsegram
||All green leafy vegetables.|
||Oilseeds such as dry coconut, gingelly seeds
(til), mustard seeds, asafoetida (hing), dry cloves, coriander and cumin seeds,
||Figs and all dry fruits such as cashewnuts,
almonds, dried figs, etc.|
||All kinds of fish.|
||Snail, mutton muscle.|
||Milk and milk products such as milk, cheese, khoa,
curds, skimmed milk powder, whole milk powder, and cottage
Table 1.2 Foods rich in phosphorus
||Rich sources of
||Cereals such as bajra, barley, millet, jowar, dry
maize, ragi, oatmeal|
||Soya bean. Moderate sources of phosphorus are bengal gram
Cowpea (chawli), rajmah, greengram and moong)
||Almond, cashewnuts, gingelly seeds (til),
mustard seeds, pistachio,|
Cumin seeds poppy seeds.
||Milk powder, milk|
Table 1.3 Foods rich in oxalic acid
||Rich sources of
||Horsegram (kuleeth), kesari dal|
||Almonds, cashewnuts, gingelly seeds, ripe chillies,
||Cocoa, coffee, tea|
||Green leafy vegetables such as amaranth, curry
leaves, drumstick leaves, mustard leaves, neem leaves, colocasia leaves, dry
lotus stem, green plant|
Table 1.4 Purine rich foods
The aim of this diet is to control or decrease the increased level of uric acid in your blood:
If you are overweight, it is necessary that you should reduce your weight. The following foodstuffs should be restricted.
|Foods with high Purine
- Organ meats such as kidney, liver, pancreas, brain.
- Sweet breads.
- Meat extracts.
|Foods with moderate amounts of
- Shell fish
- Custard apple
|Foods with small amounts of Purine
- Dry beans