Dietary Recommendations for Kidney Stones

A number of dietary factors can help to reduce the risk of kidney stones. Since kidney stones often contain calcium,1,2 people may wonder if they should limit dairy foods to reduce the risk. In fact, research shows that people with lower dietary calcium intakes actually have an increased risk of kidney stones.2 Health authorities recommend adequate dietary calcium intakes from foods to reduce the risk of kidney stones.3-5

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Our kidneys play a number of vital functions helping to regulate fluid, produce hormones and remove waste products from our bodies. Kidney stones are small, hard stones made of mineral and acid salt crystals, which form inside the kidneys. The most common type (70-80%) are calcium oxalate stones and the main mechanism involves the calcium/oxalate balance in urine.1,2 

Kidney stones are common and appear to be on the rise in recent years.1 According to The Kidney Foundation of Canada, about 12% of men and 6% of women will have a kidney stone during their lifetime.1 Having had one kidney stone increases the chance of having another.1 

Risk factors for kidney stones include family history, certain medical conditions and medications, as well as a number of dietary factors, such as insufficient fluid and dietary calcium intakes.1,2 Symptoms can include severe pain, nausea, vomiting, fever and blood in the urine.1,2 Since kidney stones often cause severe pain and may lead to chronic kidney disease, prevention is key. 

Diet and kidney stone research and recommendations

A 2020 meta-analysis examined the evidence on dietary factors for the primary prevention of kidney stones.6 This review identified a number of protective factors including fluid and water intake, a DASH-style diet (which emphasizes milk products, vegetables and fruit), dietary calcium and potassium, vegetables, fruit, dietary fibre, coffee, tea and alcohol. Whereas risk factors identified by this study included obesity, dietary sodium, fructose, meat, animal protein and soda. A 2021 meta-analysis that investigated the effect of diet and fluid intake on recurrent kidney stones confirmed that fluid intake significantly reduces the recurrence of kidney stones.7 This review also found that a normal calcium, low-sodium diet markedly reduces calcium stone recurrence. However, the findings from this study suggest that a low-protein diet, with or without fibre, does not affect the recurrence of calcium stones. 

The Kidney Foundation of Canada and the U.S. National Kidney Foundation recommend a number of general dietary strategies to help reduce the risk of kidney stones.1-4 These include drinking plenty of fluids to avoid dehydration and make urine less concentrated.1,4 Low water intakes substantially increase kidney stone risk, so adequate fluid intakes are paramount.5 Consuming enough dietary calcium from foods such as milk, yogurt and cheese is also recommended.4 Research shows that higher dietary calcium intake from foods is associated with a lower risk of kidney stones.1,5 Other healthy eating habits such as avoiding too much salt and sugar are important as well.4

In practice

Adequate intakes of fluids and dietary calcium (from foods such as milk products) are among the evidence-based dietary strategies recommended to help reduce the risk of kidney stones.3-5 Kidney foundations encourage people to:1-4 

  • Drink plenty of fluids (more than 2,500 mL per day), especially water;
  • Consume enough calcium from foods such as milk and milk products; 
  • Opt for calcium-rich foods to meet recommendations, rather than supplements;
  • Limit soda and fruit drinks sweetened with high fructose corn syrup;
  • Avoid eating too much salt and sugar.

People with kidney stones may also be advised to limit foods high in oxalates and purines.

People who are prone to kidney stones may also be advised by their health care provider to eat moderate amounts of protein and to avoid high intakes of foods high in certain compounds.3,4 These compounds include oxalates (found in plant foods such as spinach and strawberries) and purines (found in red meats, organ meats and shellfish).3,4 People should also consult a health professional before taking fish liver oil, vitamin or mineral supplements, since some supplements may increase the chances of kidney stone formation in some individuals.4  

Foods high in oxalates, such as soy products, dark green leafy vegetables like spinach, rhubarb, beets, wheat bran, nuts, seeds, chocolate and strawberries contribute to raising urine oxalate levels.4,8 Low dietary calcium intake has been found to increase the formation of calcium oxalate stones.4 When higher dietary calcium is present in the digestive tract, it binds to oxalates which reduces their absorption and therefore their elimination by the kidneys.4 High salt intakes should also be avoided to reduce the risk of kidney stone formation. 

Evidence on dietary calcium and milk products

There is good evidence that dietary calcium and milk products do not increase the risk of kidney stones. In fact, they are recommended to reduce the risk of kidney stone formation.3,4 Many studies have investigated different types of fluids and kidney stone risk. A 2015 dose-response meta-analysis found that higher milk intake was not associated with the risk of kidney stone formation.9 Water intake was associated with a reduced risk of kidney stones. 

Prospective analyses of the Health Professionals Follow-up and Nurses’ Health Studies examined the association between dietary calcium and the risk of developing symptomatic kidney stones over 56 years of follow-up.10  Higher dietary calcium from either dairy or non-dairy sources was associated with significantly lower kidney stone risk. 

The 2020 meta-analysis that explored the evidence on a wide range of dietary factors identified dietary calcium and a DASH-style diet among the factors associated with a reduced risk of kidney stones.6 However, it is important to note that this review also reported that some studies suggest that, contrary to dietary calcium from food sources, calcium supplements (especially when taken with vitamin D) may be associated with an increased risk of kidney stones.

While more research is needed on calcium supplements, kidney foundations in both Canada and the U.S. caution that some calcium supplements (which often contain vitamin D) may increase the risk of kidney stones.1,4 They therefore suggest that food sources are preferable. Thus, it’s best for people to check with their health care professional before taking supplements.  

Understanding the role of dietary calcium in kidney stones 

The bottom line is there’s good evidence that higher dietary calcium from food sources does not lead to kidney stones. In fact, sufficient dietary calcium intake, from foods such as milk products, is one of the key evidence-based dietary strategies recommended to help reduce the risk of kidney stones.3,4 The Canadian Urological Association and the U.S. National Kidney Foundation recommend calcium intakes of 1000 to 1200 mg per day (which is in line with the Recommended Dietary Allowance recommendations for adults) to help prevent kidney stones.4,5 Consuming 3 daily servings of milk products, such as milk, yogurt and cheese, which are reliable sources of calcium, is a good way to meet these daily calcium recommendations.4

Milk Products and Kidney Stones: A Review of the Evidence

View the evidence

Systematic reviews with meta-analyses and large prospective cohort studies have explored associations between calcium, milk products and kidney stones. Current evidence indicates that dietary calcium, and milk products which are an important source of dietary calcium, may reduce the risk of developing kidney stones.

Highlights

  • Adequate dietary calcium is recommended to prevent kidney stones.
  • Milk and milk products are not associated with kidney stone formation and may in fact reduce the risk.

Synopsis

Kidney stone formation, also known as nephrolithiasis, affects about 12% of men and 6% of women in Canada1 and increases the risk of chronic kidney disease. Kidney stones are small, hard stones made of mineral and acid salt crystals, which are formed inside the kidneys.

Calcium oxalate stones are the most common type of kidney stones.1 The main mechanism involves the calcium/oxalate balance in urine. Foods high in oxalates such as rhubarb, soy products, and nuts contribute to raising urine oxalate levels.2,3 Some research suggests that high intakes of protein deriving from meat, fish, and poultry may also increase the risk of kidney stones, whereas vegetable protein may have a protective effect.4 Based on the evidence, drinking enough water, consuming foods like milk, yogurt, and cheese to achieve recommended dietary calcium intakes, eating enough vegetables and fruits (that do not contain very high levels of oxalates) and limiting salt intakes help to reduce the risk of recurrent kidney stones.4

Many studies have examined the associations between calcium, milk products and kidney stones. Based on the sum of the evidence, dietary recommendations for kidney stone prevention encourage adequate dietary calcium intakes from foods such as milk products.3,5 Adequate dietary calcium is among the factors associated with a reduced risk of kidney stone formation and milk and milk products are an important source of dietary calcium.6-9  

Evidence on calcium

A 2021 systematic review and meta-analysis investigated the effect of the dietary treatment and fluid intake on the prevention of recurrent calcium stones.6 This meta-analysis of six randomized controlled trials, with a total of 824 participants, concluded that:

  • A normal calcium, low-sodium diet markedly reduces the recurrence of calcium stones;
  • A low-protein diet, with or without fibre, does not affect calcium stone recurrence;
  • Fluid intake reduced the recurrence of calcium stones.

A 2020 systematic review and meta-analysis examined dietary and lifestyle factors for the primary prevention of nephrolithiasis.7 This study found that dietary calcium was among several protective factors associated with a reduced risk of kidney stones.

  • Dietary calcium was associated with a 17% reduced risk of kidney stones.
  • Calcium supplementation alone was associated with a 16% increased risk of kidney stones based on meta-analysis of observational studies, but not randomized controlled trials. 
  • Co-supplementation with calcium plus vitamin D was a significant predictor of kidney stones.
  • The DASH-style diet (which emphasizes milk products, vegetables and fruit and is lower in sodium) was associated with a 31% reduced risk of kidney stones.  

Evidence on milk and milk products

A 2015 dose-response meta-analysis investigated the association between different types of fluids and the risk of kidney stones.8 The analysis consisted of 10 prospective cohort and 5 case-control studies, with a total of 351,081 participants. 

  • Higher milk intake was not associated with the risk of kidney stone formation.
  • Each 500 mL increase in water intake was associated with a 7% reduced risk of kidney stones.

Taylor and Curhan conducted prospective analyses of the Health Professionals Follow-up Study (n=30,762 men), the Nurses’ Health Study (n=94,164 women) and the Nurses’ Health Study II (n=101,701 women).9 The authors examined the association between dietary calcium from dairy and non-dairy sources and the risk of incident symptomatic kidney stones over 56 years of follow-up.

  • Higher dietary calcium from either dairy or non-dairy sources was independently associated with lower kidney stone risk.
  • The highest (~816-937 mg/day) compared to the lowest (143-181 mg/day) quintile of dairy calcium was associated with a 17% to 24% reduced kidney stone risk.
  • The highest (~439-460 mg/day) compared to the lowest (256-272 mg/day) quintile of non-dairy dietary calcium was associated with an 18% to 29% reduced kidney stone risk.

Potential mechanisms

Hypercalciuria (or excessive urinary calcium excretion) is the most common metabolic abnormality associated with kidney stones.10 However, urinary oxalate has been reported to be a more powerful risk factor for stones than urinary calcium.11

Decreasing dietary calcium intake is not a recommended strategy for the prevention of calcium stones.4,10 Low dietary calcium intake has been found to increase calcium oxalate stone formation. Since calcium binds with oxalate in the digestive tract, oxalate is more available for intestinal absorption when dietary calcium is limited, leading to greater urinary oxalate excretion through the urine and a greater possibility of kidney stone formation. Conversely, increased dietary calcium intake inhibits intestinal oxalate absorption by binding to dietary oxalate and forming calcium oxalate, thereby reducing oxalate excretion.3,10

Furthermore, low calcium diets do not appear to be successful in reducing calciuria. In addition, limiting calcium from dairy products may lead to increases in other animal proteins (meat, fish, poultry), which increase calciuria and the risk of kidney stones.4

The Kidney Foundation of Canada notes that while moderately high calcium intakes from dietary sources, such as dairy foods, are associated with a lower risk of kidney stones, some calcium supplements (which often contain vitamin D) may increase the risk of stones.1 More research is needed to fully elucidate the role of supplemental calcium in kidney stone formation. In the meantime, the Canadian Urological Association and U.S. National Kidney Foundation recommend a prudent food-first approach to achieve calcium intakes of 1000 to 1200 mg per day (in line with the Recommended Dietary Allowance recommendations for adults) to help reduce the risk of kidney stones.12,13 A practical way to meet this calcium recommendation is to include three daily servings of milk products such as milk, yogurt, and cheese in the diet.13

Conclusions

There is good evidence indicating that dietary calcium and milk products do not increase the risk of kidney stones. In fact, adequate intakes of dietary calcium from foods such as milk products are recommended to reduce the risk of kidney stone formation. Randomized controlled trials of high versus low intakes of milk products and dietary calcium versus calcium supplements are needed to provide more definitive answers regarding supplemental calcium and kidney stone formation.

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