Do Cashews Cause Kidney Stones?

Cashews are not a major driver of kidney stones for most people eating normal portions, but they do contain enough oxalate to matter if you eat large amounts regularly or already have a history of calcium oxalate stones. Measured against other tree nuts, cashews fall in a middle zone: their gastric soluble oxalate is relatively low, but the fraction that becomes available for absorption deeper in the intestine is moderate. One published case of irreversible kidney failure linked to daily cashew consumption brought the question into sharper focus, though the quantities involved were far beyond a typical snack.

What Makes a Nut Risky for Kidney Stones

The vast majority of kidney stones are made of calcium oxalate. Oxalate is a natural compound found in many plant foods, and when it reaches the kidneys in high enough concentrations, it can bind with calcium in the urine and crystallize. People whose urine is highly supersaturated with calcium oxalate have roughly six to seven times the odds of being stone formers compared to those with low supersaturation levels.

Not all oxalate in food ends up in your urine, though. The amount that actually gets absorbed depends on its solubility in the gut, what else you ate alongside it, and your individual gut biology. About half of the oxalate in a typical person’s urine comes from the diet, and the other half is produced internally by the body’s own metabolism.

Where Cashews Actually Rank Among Nuts

A study measuring oxalate levels across a range of common nuts found that cashews fell into the lower category for gastric soluble oxalate, clustering with peanuts and pecans in a range of about 147 to 250 milligrams per 100 grams of nut. That is meaningfully less than almonds, Brazil nuts, and pine nuts, which ranged from roughly 492 to 557 milligrams per 100 grams. But when the researchers tested intestinal soluble oxalate, the fraction that dissolves under conditions resembling deeper in the gut where absorption actually happens, cashews moved up. They landed in a higher group alongside almonds and Brazil nuts, at about 216 to 305 milligrams per 100 grams. Pine nuts topped the list for intestinal soluble oxalate at 581 milligrams, while chestnuts and roasted pistachios were far lower.

That distinction between gastric and intestinal solubility matters because it is the intestinal fraction that largely determines how much oxalate your body takes in. A nut can look relatively safe based on one measurement and less safe based on another. Cashews are a good example of that split personality: lower risk on the surface, moderate risk once you look at what the gut is actually absorbing. The researchers themselves concluded that people prone to kidney stones should moderate their consumption of certain nuts, with cashews somewhere in the middle of the spectrum rather than at the extremes.

What the Absorption Studies Show

Raw oxalate content does not tell the full story. The percentage of oxalate your body actually absorbs from a food, known as its bioavailability, varies a lot. A study measuring absorption from almonds found that about 6 percent of the oxalate made it into the body from a single meal, which was notably higher than the roughly 2 percent absorbed from black beans, even though beans contain considerable oxalate too.

⁴

An earlier study looking at peanuts and almonds specifically found that each caused a moderate bump in urinary oxalate excretion, on the order of 3 to 5 milligrams per serving, with bioavailability in the range of about 3 to 4 percent.

⁵

Cashew-specific absorption data are thinner, but given their intestinal oxalate levels sitting in a similar range to almonds, you can reasonably expect a comparable order of magnitude. A single handful of cashews is unlikely to cause a dramatic spike in urinary oxalate for someone with otherwise normal kidney function. The trouble starts when portions grow large, frequency goes up, or other risk factors pile on.

The Case Report That Raised Red Flags

The most alarming clinical evidence linking cashews to kidney damage comes from a published case of a patient who ate about 100 grams of cashew nuts every day for several months and developed acute oxalate nephropathy, a condition where calcium oxalate crystals deposit directly into kidney tissue. The damage was severe enough to cause irreversible kidney failure.

⁶

One hundred grams a day is a lot of cashews. That is roughly two-thirds of a cup, consumed daily without breaks, for months. A standard recommended portion of nuts is about 28 to 30 grams, so this patient was eating more than three servings a day, every day. The case illustrates that cashews can absolutely deliver enough oxalate to cause serious harm, but it also highlights that the harm came from chronic, heavy overconsumption rather than normal snacking.

Case reports like this one should not be dismissed, but they also should not be generalized too broadly. They are valuable because they show what is possible under extreme conditions. For a person with healthy kidneys who eats a moderate amount of cashews alongside other foods, this scenario is not a realistic risk.

Calcium and the Counterintuitive Protective Effect

One of the most commonly misunderstood aspects of kidney stone prevention is the role of calcium. Many people assume that since stones are made of calcium oxalate, eating less calcium should help. The opposite tends to be true. When you eat calcium alongside oxalate-containing foods, the calcium binds with oxalate in the gut, forming insoluble crystals that pass through you without being absorbed. That means less oxalate reaches the kidneys.

⁶

Magnesium has a similar effect. It can also bind oxalate in the digestive tract and reduce the amount that gets absorbed. Cashews contain a decent amount of magnesium, around 80 to 85 milligrams per ounce, which is one of the things that makes their risk profile less straightforward than “they contain oxalate, therefore they are bad.” The magnesium and other minerals in the nut itself may partially offset the oxalate they deliver.

Research on diet and stone formation supports this pattern more broadly. Diets low in calcium are associated with both first-time and recurrent stones, while high sodium and high animal protein raise the risk by increasing urinary calcium and uric acid and reducing urinary citrate.

⁷

So the practical takeaway is not to eat cashews in isolation on an empty stomach if you are worried about oxalate. Pair them with calcium-rich foods, or eat them as part of a mixed meal. A handful of cashews with yogurt, for example, is likely to deliver far less absorbable oxalate than the same handful eaten alone.

Phytate as a Hidden Protector

Cashews, like most nuts and seeds, contain phytate, a compound often maligned in nutrition circles for reducing mineral absorption. But phytate has an underappreciated upside: it inhibits calcium oxalate crystallization. Even after the body breaks phytate down, its breakdown products still suppress stone formation.

⁸

Oral studies have indicated that phytate may reduce urinary calcium stone formation along with other forms of pathological calcification.

⁹

This means that nuts, including cashews, come with built-in chemistry that partially counteracts their own oxalate content. That does not make them stone-proof, but it does mean the raw oxalate number on a chart overstates the actual risk of eating the whole food. Isolating one compound from a nut and extrapolating the danger tends to miss the full picture of how these nutrients interact during digestion.

Your Gut Bacteria Play a Role Too

One reason some people can eat plenty of oxalate-rich food without forming stones while others cannot is the composition of their gut microbiome. Certain bacteria, particularly a species called Oxalobacter formigenes, break down oxalate in the intestine before it has a chance to be absorbed. In a clinical study, people colonized with this bacterium had about 14 percent lower urinary oxalate on average when eating a high-oxalate diet, with stool oxalate levels dropping by more than half.

¹⁰

Antibiotic use can wipe out these bacteria, which may explain why some people develop oxalate-related problems after a course of antibiotics even if their diet has not changed. This also means that two people eating identical portions of cashews could end up with very different amounts of oxalate in their urine, depending on what is living in their gut. It is one of the reasons blanket dietary restrictions can feel overly blunt. Your personal risk from a given food depends not just on the food but on your particular biology.

Cashew Milk and Processed Cashew Products

The rise of plant-based milks has introduced cashew-derived beverages into many diets, and these products carry their own oxalate load. Among plant-based milks, almond milk was found to have the highest oxalate concentration, followed by cashew milk, hazelnut milk, and soy milk.

¹¹

If you are switching from dairy to cashew milk and drinking several glasses a day, you could be taking in more oxalate than you realize, especially because the liquid form may allow for higher bioavailability than chewing a solid nut. People with a history of calcium oxalate stones who have moved away from dairy should think about this, particularly since dairy milk provides calcium that actively binds oxalate in the gut. Replacing it with a nut-based milk removes that protective calcium while adding oxalate, a double shift in the wrong direction.

Does Roasting Change Anything?

Most cashews you buy are already roasted or heat-treated, so it is worth knowing whether processing makes a difference. Research on how roasting affects anti-nutritional factors in plant seeds found a modest reduction in oxalate content after roasting, though the decrease was relatively small.

¹²

Do not expect roasting to meaningfully change your risk profile. It is a marginal reduction, and the baseline oxalate content in cashews is not so high that a small percentage drop transforms them from problematic to safe. If you are managing oxalate intake for medical reasons, portion size is going to matter much more than whether the cashew was raw or roasted.

Who Actually Needs to Be Careful

The evidence suggests that people who excrete more than about 25 milligrams of oxalate per day in their urine may benefit from reducing dietary oxalate.

If you fall into one of the following groups, paying attention to cashew intake is more important than it would be for the average person:

Recurrent stone formers: If you have had a calcium oxalate stone before, your risk of forming another is elevated, and dietary oxalate management is a reasonable precaution.
People with gut absorption issues: Conditions that increase oxalate absorption, such as inflammatory bowel disease, gastric bypass surgery, or chronic diarrhea, can amplify the effect of dietary oxalate.
Low calcium dieters: If you avoid dairy and do not supplement calcium, there is less mineral in the gut to bind oxalate before it gets absorbed.
Heavy consumers: Anyone eating several ounces of cashews daily for extended periods is in the territory where the case report matters.

For the general population, a standard serving of cashews, around one ounce or roughly 18 to 20 nuts, is not a meaningful kidney stone risk factor. The overall dietary pattern matters far more than any single food. A large population-based study of over 10,000 adults in Iran found that kidney stone prevalence was associated with higher carbohydrate and copper intake but not with the broader array of macronutrients and micronutrients examined.

¹³

That study did not single out nuts or oxalate as independent risk factors in that population, which is a useful reminder that kidney stone formation is driven by the combined effects of hydration, sodium intake, animal protein consumption, body weight, and genetics, not by whether you put cashews on your salad.

The Intestinal Transport System Behind Individual Risk

Part of the reason oxalate sensitivity varies so widely between people lies in the molecular machinery of the intestine. Specific membrane transport proteins, belonging to a family of anion exchangers, actively move oxalate across the intestinal wall. These transporters handle both the absorption of dietary oxalate into the bloodstream and, in the other direction, the secretion of internally produced oxalate back into the gut for elimination.

¹⁴

Genetic variation in these transporters could explain why some people handle high-oxalate diets without trouble while others develop elevated urinary oxalate even with moderate intake. This is still an active area of research, and there is no widely available genetic test for oxalate absorption capacity. But it helps explain why your friend can eat a bag of cashews with no consequences while someone else forms a stone from what seems like a normal diet. The intestine is not a passive tube; it is actively regulating how much oxalate gets through, and that regulation differs from person to person.

Practical Steps If You Love Cashews

You do not need to give up cashews to protect your kidneys unless your doctor has specifically told you to restrict oxalate. A few habits can reduce whatever modest risk exists:

Keep portions reasonable: One ounce, about a small handful, is a standard serving. Going through a full container in an afternoon is where risk accumulates.
Eat them with meals: The calcium and magnesium in other foods will bind some of the oxalate before your body absorbs it.
Stay hydrated: Dilute urine is the simplest way to keep any dissolved oxalate from reaching concentrations that favor crystallization.
Watch your sodium: High salt intake increases the amount of calcium your kidneys excrete into urine, giving oxalate more material to crystallize with.
Do not drop dairy to add nut milks without thinking it through: The calcium in dairy is protective, and removing it while adding oxalate from cashew milk shifts the balance unfavorably.

If you have had a calcium oxalate stone, a 24-hour urine collection is the single most useful test. It tells you exactly how much oxalate, calcium, citrate, and other stone-forming substances are in your urine, and your urologist can tailor dietary advice based on your actual chemistry rather than generic food lists. For everyone else, cashews remain a nutritious snack that fits comfortably into a stone-preventive diet when eaten in normal amounts.

1
PubMed Central. Relative Supersaturation of 24-Hour Urine and Likelihood of Kidney Stones
2
American Physiological Society (AJP Renal Physiology). Dietary oxalate and kidney stone formation
3
Journal of Food Composition and Analysis. Soluble and insoluble oxalate content of nuts
4
PubMed. Assessment of oxalate absorption from almonds and black beans with and without the use of an extrinsic label
5
PubMed. A further study of oxalate bioavailability in foods
6
CMAJ. Oxalate nephropathy from cashew nut intake
7
Springer Nature. The Role of Diet in Kidney Stone Pathogenesis and Prevention
8
PubMed Central. Phytate Dephosphorylation Products Also Act as Potent Inhibitors of Calcium Oxalate Crystallization
9
PubMed Central. The Relevance of Phytate for the Treatment of Chronic Kidney Disease
10
PubMed Central. Inducing Oxalobacter formigenes Colonization Reduces Urinary Oxalate in Healthy Adults
11
PubMed Central. Plant-Based Milk Alternatives and Risk Factors for Kidney Stones and Chronic Kidney Disease
12
ANACHEM Journal. Impact of Roasting on the Proximate and Anti-Nutritional Factor of Commonly Consumed Plant Seeds in Nigeria
13
BMC Public Health. Kidney stones and dietary intake in adults: a population-based study in southwest Iran
14
SpringerLink / Urolithiasis. The role of intestinal oxalate transport in hyperoxaluria and the formation of kidney stones in animals and man