12/10/2024
Kidney Stones: Dietary Management
The kidney is an organ that functions as a waste filter in the body. When there is too much waste filtered into the kidneys and not enough liquid to dissolve it, crystals that are commonly known as kidney stones can form. Kidney stones, or renal calculi, are hard solid deposits formed out of minerals and salts in the kidney. Kidney stone can be as small as a grain of salt, but the size can gradually increase if it is not removed.
There are four main types of kidney stones. The most typical form is calcium stones, which are made from either the combination of calcium with oxalate (more common) or with phosphate. Another common type is uric acid stones, formed when there is high uric acid waste. The more atypical types are struvite stones which are caused by infections of the urinary tract, and cystine stones which are formed as a result of a hereditary disorder called cystinuria.
Untreated kidney stones can lead to bloody urine, severe pain, urinary tract infection, and kidney disease. Medical treatments and dietary modification can be done to treat and prevent the recurrence of kidney stones, individualised based on the type of stone. The general dietary recommendation to reduce the chances of kidney stones formation are as follows:
1. Drink more fluid
Drink at least around 2.5 litres or 10 cups of fluid daily, including other fluids such as milk and lemonade. With the exception of grapefruit juice, sweetened beverages, and alcohol, adequate fluid helps to produce less concentrated urine and ensure good urine volume, decreasing the risk of stone formation.
2. High fibre intake
High dietary fibre intake can reduce the formation of oxalate and calcium absorption, hence, can reduce the risk of stones formation. Research has also shown that greater dietary fibre intake is protective against kidney stones formation. Therefore, one should consume 5 servings of fruits and vegetables, and opt for whole grain products to ensure adequate fibre intake.
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Precisely for calcium oxalate stone, the recommendations are as follows:
1. Low sodium intake
High sodium intake can increase urinary calcium excretion, causing kidney stones. Thus, consumption of food high in sodium such as salt, sauces, seasonings, fast food, junk food, sodium bicarbonate, processed meat, canned food, pickles, and salted food (anchovies, dried shrimp et cetera) should be reduced.
2. Low oxalate intake
High dietary oxalate intake can cause oxalate to combine with calcium in the kidney, forming calcium oxalate stone. Thus, high oxalate foods which include spinach, celery, cocoa products, beets, rhubarb, citrus peels, strong black tea, nuts, wheat germ, wheat bran, some berries, and star fruit should be limited.
3. Adequate calcium intake (but not from supplement)
Inadequate calcium leads to loss of minerals from the bone, which in turn can increase urinary calcium excretion and subsequently, the risk of oxalate stone formation. Consumption of calcium with meals can help reduce the absorption of oxalate. Therefore, one should consume three servings of calcium-rich food such as milk, cheese, and yoghurt with meals. Meanwhile, calcium supplements, especially if consumed separately from meals can increase calcium excretion without the beneficial effect on oxalate, thus increasing the risk of stones.
4. Moderate protein intake
High protein intake can lead to higher urinary calcium excretion, causing kidney stones. So, consumption of protein, especially of animal sources, should be in moderation. One should consume moderate serving which is around half palm-sized animal protein per meal (around 120 to 150 grams daily).
5. Avoid vitamin C and D supplements
Oxalic acid is one of the major end products of vitamin C metabolism. Excessive consumption through supplementation may lead to high oxalic acid excretion in the urine, leading to stone formation. While there is currently no evidence that vitamin D supplement can directly cause kidney stones, some research suggests that Vitamin D supplementation might increase the risk of stone formation as it can elevate the level of urinary calcium. Thus, supplementation of vitamin C and D without health professionals’ recommendation (i.e in case of deficiency et cetera) is not advised.
For uric acid stones, the followings are recommended:
1. Low purine intake
Uric acid is the end product of purine metabolism. Excessive purine consumption can lead to high uric acid level, which then can cause stones formation. High purine food including organs, game meat, fish egg, sardine, anchovies, mackerel, tuna, some seafood, yeast, budu, belacan, cencalok, and meat extract should be avoided, while medium purine food such as meat, chicken, legumes, and other fish should be consumed in moderation. As for vegetable and fungi high purine sources such as broccoli, spinach, asparagus and cauliflower, research has shown that they do not cause an increase in uric acid level.
2. Avoid alcoholic beverages
Alcohol can increase uric acid production and reduce uric acid excretion by the kidneys. This leads to uric acid accumulation and can cause stones production. Some alcoholic beverages such as beer also contain high purine levels. Abstaining from alcohol of all types can reduce risk of stones production.
3. Avoid sweetened food and beverages / 避免食用加糖食品和饮料
Sweetened food and beverages typically contain fructose, which is broken down into purines and consequently, into uric acid in the body. This in turn can increase risk of uric acid stone formation. Thereby, sweetened food and beverages such as syrups, breakfast cereal bars, candies, carbonated drinks, 3 in 1 drinks, and so on should be avoided.
