Low Oxalate Diet For Kidney Stones — Symptoms and Prevention
Introduction
Kidney stones, or renal calculuses, are hard crystalline mineral materials formed within the kidney or urinary tract. Kidney stones are typically composed of calcium oxalate but can also contain other substances such as uric acid or struvite. They vary in size, with some being as small as a grain of sand, while others can grow to be quite large and can cause severe pain as they pass through the urinary tract.
Table of contents
Types of Kidney Stones
Understanding the type of kidney stone a person has is essential for determining the underlying cause and developing an appropriate treatment plan (1, 2).
The types of kidney stones include:
- Calcium stones: Calcium stones are the most common type of kidney stones, usually in the form of calcium oxalate and calcium phosphate. Calcium oxalate stones are commonly envelope or dumbbell-shaped and develop due to conditions like hypercalciuria, hyperoxaluria, and hypomagnesuria.
- Uric acid stones: These form when there is too much uric acid in the urine, often seen in people with gout or those who consume a high-purine diet. These rhomboid-shaped stones can form in individuals with high-protein diets that acidify urine pH.
- Struvite stones: Struvite stones, also called infection stones, develop in reaction to urinary tract infections and have the potential to grow, reaching significant sizes. They are associated with infections caused by urease-producing bacteria like Proteus mirabilis, Klebsiella pneumonia, Enterobacter, and Pseudomonas aeruginosa. Struvite stones, or magnesium ammonium phosphate stones, have a coffin lid shape.
- Cystine stones: Cystine stones are uncommon and typically affect individuals with a genetic condition leading to excessive cystine excretion by the kidneys.
- Mixed stones: Mixed stones consist of minerals like calcium oxalate and calcium phosphate.
Symptoms
Kidney stones and the resulting obstruction can lead to various complications, such as abscess formation, urosepsis, urinary fistula formation, scarring, narrowing of the ureter, ureteral perforation, and loss of renal function due to prolonged obstruction (2).
The symptoms of kidney stones depend on their location, whether in the kidney, ureter, or bladder. Initially, stone formation may be asymptomatic.
Symptoms are severe cramping pain (renal colic), back pain (flank pain), bloody urine (hematuria), obstructive uropathy, urinary tract infections, blocked urine flow, painful or difficult urination (dysuria), and kidney swelling (hydronephrosis).
These symptoms can lead to nausea, vomiting, and overall discomfort, impacting the individual's quality of life and the economy due to treatment costs and work absences (5, 8).
Causes of Kidney Stones
- Anatomical abnormalities in the kidneys and ureters, family history of kidney stones or previous history of kidney stones, and certain medications
- Older age, genetic factors (although changes in the gene pool occur slowly and are unlikely to account for rapid trends in stone prevalence) (3)
- Gender (conflicting results reported, with some studies showing higher risk in women and others in men), weight, and body mass index (4).
- Diminished fluid intake, low calcium consumption, and high oxalate intake are dietary risk factors for kidney stone formation.
- Increased consumption of oxalates, animal protein, and sodium-rich foods is also associated with a higher risk of developing a stone.
- Kidney stone formation is associated with various medical conditions, including obesity, diabetes mellitus, hypertension, chronic kidney disease, metabolic syndrome, and cardiovascular problems.
- Smoking, alcohol consumption, and opium use have shown associations with kidney stone risk, possibly due to factors like cadmium and lead exposure in smokers.
- Water quality (total hardness of drinking water) is also associated with the occurrence of kidney stones (3, 5, 6, 7).
Prevalence
There has been a notable rise in the prevalence and incidence of kidney stones globally, including in the United States.
These increases are observed across various demographics, suggesting widespread environmental influences. In the United States, kidney stones affect approximately 8.8% of the population, with a higher prevalence among men than women.
The majority of kidney stones are composed of calcium oxalate (61%), followed by calcium phosphate (15%) and uric acid stones (12%) (5).
How To Prevent Kidney Stone Formation?
It is essential to address the underlying causes to prevent kidney stone formation. Here are some key strategies:
- Stay well-hydrated: Maintain a urine output of at least 2 liters daily by increasing your water intake. Sufficient fluid intake helps reduce urinary saturation and dilutes substances that promote calcium oxalate crystallization.
- Dietary adjustments: Follow a diet that is low in oxalate and high in calcium, which can help prevent absorptive hyperoxaluria. Increase your consumption of potassium-rich fruits and vegetables and avoid foods high in oxalate.
- Reduce sodium intake: High sodium intake can increase the risk of kidney stones by reducing renal tubular calcium reabsorption and increasing urinary calcium. Limit your consumption of sodium-rich foods.
- Limit animal protein: Animal proteins can increase the acid load in the body, leading to a decrease in urine pH and increased urinary calcium excretion. Reduce your intake of meat, fish, and poultry.
- Calcium intake: Low calcium intake can lead to increased oxalate absorption and the risk of stone formation. Calcium supplements may help reduce oxalate absorption.
- Vitamin C supplementation: Limit vitamin C supplementation, as it may lead to stone formation due to the conversion of ascorbic acid to oxalate.
- Alkalinize urine: Alkalinize urine by eating a diet high in fruits and vegetables, taking supplemental or prescription citrate, or drinking alkaline mineral waters.
- Control underlying conditions: If you have gout or cystinuria, it is essential to control them to prevent stone formation (8, 9, 10, 11).
Low Oxalate Diet and Kidney Stones
A diet high in soluble oxalates can lead to excessive urinary excretion of oxalate (hyperoxaluria) and an increased risk of kidney stone formation.
Individuals prone to kidney stones should minimize their intake of foods high in oxalates and maintain calcium consumption (21,22,23).
It's essential to restrict the concentration of calcium oxalate in the urine to prevent calcium oxalate stone formation, as this affects stone risk. People should be cautious of consuming excessive oxalate and low calcium in a single meal, as this can temporarily increase oxalate absorption and urine supersaturation with calcium oxalate.
Recommended Daily Oxalate Intake
The average daily intake of oxalate in diets is estimated to be between 70-150 mg (12).
What to Eat and What to Avoid?
Most fruits and berries have low to moderate oxalate content (13, 14). Certain vegetables contain less than 10 mg oxalate per 100 g of fresh weight, while others have high amounts (100 mg oxalate per 100 g of fresh weight) (15, 16, 17).
Beverages like wine may have a protective effect against kidney stones, with moderate consumption decreasing the risk by 39-58%. However, further research is required to establish causality (18, 19, 20).
| High Oxalate Foods To Avoid (mg/100g) | Low Oxalate Foods To Eat (mg/100g) |
| Vegetables | |
| Swiss chard (874-1458.1mg) | Broccoli (20mg) |
| Garden rhubarb (690mg) | Eggplant (16mg) |
| White bean (548mg) | Onion (5mg) |
| Rhubarb (460-805mg) | Cauliflower (5mg) |
| Sweet potato (495.6mg) | Cucumber (4mg) |
| Spinach (490mg) | Asparagus (2mg) |
| Fruits | |
| Goji berries (138mg) | Kiwi (20mg) |
| Pomegranate (121mg) | Banana (20mg) |
| Carambola (111mg) | Apple (11mg) |
| Jujube (64mg) | Cherry (6mg) |
| Feijoa (60mg) | Orange (2mg) |
| Grains | |
| Buckwheat (133mg) | Millet (13mg) |
| Quinoa (106mg) | Lentil (13mg) |
| Couscous (65mg) | Rice (4mg) |
| Nuts | |
| Almond (296mg) | Macadamia (42mg) |
| Peanut (76mg) | Pecan (37mg) |
| Walnut (54mg) | Ginkgo nuts (26mg) |
Downsides of Low Oxalate Diet
A low oxalate diet may lead to several downsides:
- Reduced calcium availability: A low oxalate diet can reduce calcium availability since oxalates bind to calcium, limiting absorption. Calcium is crucial for bone health and various bodily functions.
- Increased risk of calcium deficiency: Individuals on a low oxalate diet, especially vegetarians who consume fewer animal products rich in calcium, may be at a higher risk of calcium deficiency. This deficiency can lead to weakened bones (osteoporosis) and other health issues. Women, who generally require higher amounts of calcium in their diet, may be at an increased risk on a low oxalate diet due to reduced calcium availability.
- Dietary restrictions: Following a low oxalate diet may require avoiding certain foods that are otherwise nutritious, such as spinach, beet, and rhubarb, which are high in oxalates. Avoiding high oxalate foods can limit the variety in one's diet, potentially leading to monotony and nutrient deficiencies if not carefully managed (12).
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