What is oxalate

Oxalate in the mammalian body originates from two main sources: endogenous (body in your liver) production and external source via dietary intake. The ratio between liver-generated and absorption-related sources depends on oxalate content in ingested food. Both sources have a potentially important role in increasing oxalate concentrations in plasma and urine. Oxalate is a toxic simple organic acid that is ubiquitous in the plant kingdom and widely consumed in normal human diets as a component of fruits, vegetables, grains and nuts 1). The normal daily intake of oxalate ranges from 70 to 920 mg, but strongly increases in vegetarians 2). The average daily dietary oxalate intake content in the United States is 214 mg in men, 185 mg in older women, and 183 mg in younger women; spinach accounts for > 40% of the oxalate intake 3). Despite the toxicity of oxalate to mammals, it cannot be degraded by mammalian enzymes 4). However, it can be metabolized by many gut bacteria, such as Oxalobacter formigenes and Lactobacillus acidophilus, among others 5).

Figure 1. Oxlate sources

oxalate sources

Note: OX= oxalate; Gall bl.= gallbladder; GIT= gastrointestinal tract

[Source 6)]

Factors leading to high rates of oxalate absorption from the gut include the presence of medical conditions or surgical interventions leading to steatorrhea, low dietary content in calcium and magnesium, both of which bind oxalate in the gastrointestinal tract and decrease its absorption and renal excretion, and the absence from the intestinal flora of certain species of bacteria, in particular, Oxalobacter formigenes, an anaerobic bacterium that metabolizes oxalate. The absence of this bacterium from the gut has been associated with hyperoxaluria, but bacteriotherapies involving oxalate-degrading bacteria have met with mixed results 7). While probiotics containing Oxalobacter formigenes, Lactobacillus spp., Bifidobacterium spp., or Enterococcus spp. effectively reduce urinary oxalate excretion, the bacteria and the oxalate-degrading function are often lost when probiotic use ceases and/or oxalate is removed from the diet 8). In some cases, urinary oxalate remains unchanged despite long-term administration of probiotics and persistence of oxalate-degrading microbes in the gut 9).

Oxalate is also natural chemical in your body. Oxalate is produced by many kinds of cells, including liver cells, kidney, epithelial cells and apocrine cells, among others 10), 11). Most of body oxalate is a metabolic end-product generated largely in the liver and represents 85 % to 90 % of the total oxalate circulating in blood (endogenous oxalate). An unknown proportion of the liver-produced oxalate is removed via bile secretion. The remainder (10 % to 15 %) of blood oxalate (exogenous oxalate) originates from the absorption of food in the gastrointestinal tract. The bulk (90 % to 95 %) of circulating oxalate is ultimately excreted by the kidneys, whereas some 5 % to 10 % of blood oxalate is excreted in the terminal parts of the small intestine and colon. And too much oxalate in your urine can cause serious problems.

Hyperoxaluria is defined as excessive urinary oxalate excretion, which occurs when you have too much oxalate in your urine 12). Too much oxalate in your urine can cause serious problems when the excess oxalate combines with calcium in urine to form the most common type of kidney stone, a calcium oxalate stone and has been associated with acute or chronic kidney injury 13).

Hyperoxaluria develops as a consequence of either excessive endogenous oxalate production (primary hyperoxaluria) or excessive oxalate absorption from the gastrointestinal tract. The later can be associated with enteric hyperoxaluria from fat malabsorption, e.g., in patients with Roux-en-Y gastric bypass surgery 14), jejunoileal bypass surgery 15), Crohn’s disease 16), sprue 17) or taking medications such as orlistat that cause fat malabsorption 18). Other potential culprits for excessive oxalate absorption include either excessive dietary intake of oxalate or its substrate (vitamin C) or dietary deficiency of calcium or magnesium 19).

Although there is substantial variation between individuals, urinary oxalate excretion rises in parallel with dietary oxalate intake when other variables potentially affecting oxaluria are under control 20). Chronic intake of food items with a high content of oxalate may lead to hyperoxaluria with urinary oxalate excretion similar to the degree usually seen in primary hyperoxaluria. The component of urinary oxalate excretion that is derived from gastrointestinal absorption is determined by the oxalate content of the diet and the rate of absorption of oxalate in the intestines. Food items high in oxalate include leafy vegetables, such as spinach, various nuts, e.g., peanuts, and tropical fruits, including Averrhoa carambola (starfruit) and Averrhoa bilimbi (commonly known as bilimbi or cucumber tree) 21).

The proportion of urinary oxalate that is derived from dietary oxalate is estimated to range from 10 to 50% 22). In addition to oxalate intake, intake of oxalate precursors may cause hyperoxaluria. Vitamin C (ascorbic acid), pyridoxylate, which is a combination of glyoxylic acid and pyridoxine, and hydroxyproline are potential sources of oxalate that have caused hyperoxaluric renal disease in clinical and experimental studies. Furthermore, hyperoxaluria and oxalate nephropathy may develop as a result of the oxalate salts of parenteral medications. It is well established that a large proportion of urinary oxalate is derived from the endogenous metabolism of glycine, glycolate, hydroxyproline, and dietary vitamin C 23). A recent metabolic study compared a controlled diet with 25% of protein from gelatin (2.75 g of hydroxyproline) with the same diet except with 25% of protein from whey (containing no hydroxyproline) 24). The diet that was high in hydroxyproline increased urinary oxalate excretion by 42%. Another metabolic trial demonstrated that 1000 mg of supplemental vitamin C consumed twice daily increased urinary oxalate excretion by 20 to 33% 25).

A review of oxalate load studies indicates that a peak in urinary oxalate excretion normally occurs two to four hours after the oxalate ingestion 26). Thus, it is quite possible that such transient oxalate loads on the kidney result in a transient hyperoxaluria. Interestingly, Gambaro et al have noted that the fractional excretion of oxalate was 70% higher in stone formers compared with normal individuals 27). It is plausible that a transient renal oxalate load on the kidney associated with an oxalate-rich meal might lead to renal cell injury, most likely in the proximal tubule. This may be amplified in stone formers due to an enhanced oxalate secretion and an elevated intestinal absorption 28). It has been established that oxalate can affect renal cells by either stimulating cellular proliferation or by inducing cell injury 29).

Calcium stones, including calcium oxalate stones ~ 70% and calcium phosphate stones ~ 15%, are the most common types of kidney stones. Calcium oxalate is also associated with benign breast tissue calcifications 30). Furthermore, a low-calcium diet was shown to be a significant risk factor for the kidney stones (calcium oxalate stones) disease 31). The explanation for the role of dietary calcium was that it complexed intestinal oxalate and limited its availability for absorption 32). In a study 33), a 34% increase in urinary oxalate excretion accompanied the decrease in calcium intake from 1002 mg to 391 mg per day, which is consistent with this theory. The studies of Liebman and Chai also support this role for dietary calcium in showing that supplemental calcium decreased the absorption of an oxalate load by more than 50% 34). Other observational studies have shown an inverse relation between dietary calcium and the risk for incident kidney stones 35), 36) suggested that dietary calcium may bind to oxalate in the gut, thereby limiting intestinal oxalate absorption (and subsequent urinary oxalate excretion). Indeed, the inhibitory effect of calcium ingestion on urinary oxalate excretion has been demonstrated in oxalate loading studies 37). Magnesium intake may also decrease urinary oxalate in a similar manner 38), 39).

Moreover, there is nearly universal agreement in studies of normal and stone-forming populations that the mean calcium excretion of the stone forming population is higher than that of the normal population, that the incidence of hypercalciuria (high urine calcium concentration) in the stone-forming population is 5 to 10 times above that in a normal population, and that the relative supersaturation of the urine is higher in hypercalciuric individuals than in normocalciuric individuals 40), 41). Differences in oxalate excretion are less pronounced, suggesting that if oxalate plays a role it may in part be due to effects other than by affecting relative supersaturation alone.

Currently, there are no established therapies that decrease urinary oxalate excretion in individuals with idiopathic calcium oxalate kidney stones disease. They are often advised, without substantial data to support the efficacy of this dietary recommendation, to avoid oxalate-rich foods 42).

Foods high in oxalate

Dietary hyperoxaluria has been reported after ingestion of large amounts of food products with high oxalate content for medicinal, cosmetic or weight loss purposes. Most commonly implicated vegetables and fruits are peanuts 43), Averrhoa bilimbi (commonly known as bilimbi or cucumber tree) 44), celery, carrots, parsley, beets, and spinach 45).

Even though those food products are ubiquitous in many diets, there have been few reports of renal parenchymal disease secondary to dietary hyperoxaluria 46). Bakul et al have described a case series of 10 patients who developed acute renal failure after consumption of A. bilimbi fruit juice 47). Seven patients required hemodialysis while 3 cases recovered kidney function with conservative management. While their serum creatinine values at time of diagnosis ranged from 5.5 to 12.3 mg/dL, all 10 patients recovered within 2 to 6 weeks.

Figure 2. Oxalate rich foods

oxalate rich foods

Table 1. Foods that contribute to oxalate

Cooked spinach23.1Cooked spinach25.8Cooked spinach22.0
Raw spinach17.3Raw spinach18.4Raw spinach20.3
Potatoes (whole)10.2Potatoes (whole)11.1Potatoes (whole)9.9
Cold cereal4.4Cold cereal4.3Cold cereal3.8
Oranges2.9Oranges2.5French fries2.5
French fries1.9Coffee1.7Oranges2.0
Mixed nuts1.7Cooked carrots1.7Pasta2.0
Navy beans (canned)1.7Tea1.6Pasta sauce1.9
Cookies1.6Cookies1.5English muffins1.7
Peanuts1.6Pasta sauce1.4Coffee1.7

Note 48): Spinach has 794 mg oxalate/100 g; Potato has 24.7 mg oxalate/100 g;

[Source 49)]

Table 2. Oxalate content of foods

Food ItemServing sizeOxalate CategoryOxalate Value
Spinach, cooked1/2 cupVery High755
Spinach, raw1 cupVery High656
Rhubarb1/2 cupVery High541
Rice Bran1 cupVery High281
Buckwheat Groats1 cup cookedVery High133
1 oz or 22 kernels
Very High122
Miso Soup1 cupVery High111
Wheat Berries1 cup cookedVery High98
Corn Grits1 cupVery High97
Corn Grits1 cupVery High97
Baked Potato with Skin1 mediumVery High97
Soy Flour1 cupVery High94
Bulgur, cooked1 cupVery High86
Navy Beans1/2 cupVery High76
Beets1/2 cupVery High76
Cocoa Powder4 tspVery High67
Hot Chocolate (homemade)1 cupVery High65
Brown Rice Flour1 cupVery High65
Brown Rice Flour1 cupVery High65
Cornmeal1 cupVery High64
Cornmeal1 cupVery High64
Millet, cooked1 cupVery High62
Okra1/2 cupVery High57
Bran Flakes with Raisins, Single Brand1 cupVery High57
Post Original Shredded Wheat & Bran1 1/4 cupVery High53
French Fries4 ozVery High51
French Fries (homemade or fast food)
4 oz or 1/2 cup
Very High51
1 oz or 18 kernels
Very High49
Raspberries1 cupVery High48
Soy Beans1/2 CupVery High***48
Nabisco Honey Nut Shredded Wheat Bite Size1 cupVery High47
Kellog Raisin Bran1 cupVery High46
Spoonsize Shredded Wheat1 cupVery High45
Nabisco Shredded Wheat2 biscuitsVery High42
Stevia1 tspVery High***42
Post Fruit & Fiber Dates, Raisins & Walnuts1 cupVery High41
Raisin Squares Mini-Wheats3/4 cupVery High41
Barley Flour1/2 CupVery High***41
Miso1 cupVery High40
Miso1 cupVery High40
1/2 cup, cubed
Very High40
Bagel NY Style1 BagelVery High***40
Lentil Soup1 cupVery High39
Mixed Nuts (with Peanuts)1 ozVery High39
Chocolate Syrup2 TbsVery High38
Chocolate Syrup2 TbsVery High38
Candies with Nuts (ex Snickers)2 ozVery High38
Candies with Nuts (ex Snickers)2 ozVery High38
Pancakes (dry mix)4 pancakesVery High37
General Mills Multi-Bran Chex1 cupVery High36
Post 40% Bran3/4 cupVery High36
Stuffing1 cupVery High36
Kellog Special K Low Carb1/2 CupVery High***35
Post Cranberry Almond Crunch (Morning Traditions)1 cupVery High35
Bamboo Shoots1 cupVery High35
Kellog Complete Wheat Bran3/4 cupVery High34
General Mills Total Raisin Bran1 cupVery High31
1/2 cup mashed
Very High31
1 cup or 7 nuts
Very High31
1 oz or 1/2 brownie
Very High31
Dried Pineapples1/2 cupVery High30
1/2 cup mashed
Very High30
Mashed Potatoes1 cupVery High29
Orange1 fruitVery High29
Wheat Flour, Whole Grain1 cupVery High29
Wheat Flour, Whole Grain1 cupVery High29
Fudge Sauce2 TbsVery High28
Fudge Sauce2 TbsVery High28
Kellog Frosted Mini-Wheats1 cupVery High28
Sweet Potatoes1 cupVery High28
Kellog Raisin Bran Crunch1 cupVery High27
Peanuts1 ozVery High27
Soy Protein Isolate1 ozVery High27
Carrot Juice1 cupVery High27
Kellog All-Bran Original1/2 cupVery High26
Post 100% Bran1/3 cupVery High25
Post Banana Nut Crunch1 cupVery High25
Chili with Beans1 cupVery High24
Dates1 dateVery High24
Dried Figs
5 pieces/fruits
Very High24
General Mills Oatmeal Crisp with Almonds1 cupVery High24
General Mills Raisin Nut Bran1 cupVery High24
Veggie Burger1 pattieVery High24
Brown Rice, cooked1 cupVery High24
General Mills Honey Nut Clusters1 cupVery High23
Lasagna1 servingVery High23
Lasagna with meat1 servingVery High23
Pancakes (Homemade)4 pancakesVery High22
Potato Chips1 ozVery High21
Potato Chips1 ozVery High21
Fava Beans1/2 cupVery High20
Kellog All-Bran Buds1/2 cupVery High20
Kellog Mueslix Apple & Almond Crunch2/3 cupVery High20
Soy Milk1 CupVery High***20
Celery Raw1/2 CupVery High***19
Avocados1 fruitVery High19
Cream of Wheat1 cupVery High18
approx 10 olives
Very High18
Post Great Grains Crunch Pecan2/3 cupVery High18
V8 Juice1 cupVery High18
General Mills Basic 41 cupVery High17
Mueslix2/3 cupVery High17
Post Great Grains Raisin, Dates & Pecans2/3 cupVery High17
Potato Salad1/3 cupVery High17
Pumpkin Seeds
1 cup, cooked
Very High17
Tomato Sauce1/2 cupVery High17
All-Purpose Flour1 cupVery High17
All-Purpose Flour1 cupVery High17
Brussel Sprouts Raw1/2 CupVery High***17
Burritos with beans1 burritoVery High17
Farina Cereal1 cupVery High16
Kellog Low Fat Granola with Raisins2/3 cupVery High16
Kiwi1 fruitVery High16
Peanut Butter Reduced Fat1 TbsVery High16
Refried Beans1/2 cupVery High16
Tahini1 TbsVery High16
Burritos with beans & meat1 burritoVery High16
Cake (homemade)1 pieceVery High16
Couscous1 cupVery High15
Kellog Cracklin’ Oat Bran3/4 cupVery High15
Kellog Smart Start1 cupVery High15
Lemonade (frozen from concentrate)8 ozVery High15
Quaker Low Fat 100% Natural Granola with Raisins3/4 cupVery High15
Parsnip1/2 cupVery High15
Red Kidney Beans1/2 cupVery High15
Trail Mix1 ozVery High15
Cake (store brand)1 pieceVery High15
Carrots, raw1/2 CupVery High***15
Danish Pastry Homemade1 pastryVery High14
Kellog Kashi Go Lean3/4 cupVery High14
1 oz or 48 kernels
Very High14
Post Grape Nuts1/2 cupVery High14
Tea, Brewed1 cupVery High14
Tomato Juice1 cupVery High14
Cheeseburger with bun
1 burger & bun
Very High13
Clam Chowder1 cupVery High13
Enchilada with Cheese & beef1 enchiladaVery High13
Enchilada with Chicken1 enchiladaVery High13
French Toast2 slicesVery High13
French Toast2 slicesVery High13
General Mills Fiber One1/2 cupVery High13
General Mills Nature Valley Cinnimon & Raisins Granola3/4 cupVery High13
General Mills Oatmeal Raisin Crisp1 cupVery High13
Kellog Just Right Fruit & Nut1 cupVery High13
Kellog Puffed Kashi1 cupVery High13
Nachos with Cheese6-8 chipsVery High13
Peanut Butter1 TbsVery High13
Pizza with Cheese2 slicesVery High13
Red River Cereal1/4 cupVery High13
Rice Dream1 cupVery High13
Sweet Rolls Low Fat1 pastryVery High13
Tofu3.5ozVery High13
Quaker 100% Natural Granola Oats & Honey1/2 cupVery High13
English Muffin Whole Wheat1 muffinHigh12
English Muffins Whole Wheat ONLY1 muffinHigh12
Grapefruit1/2 fruitHigh12
Grilled Cheese Sandwich1 sandwichHigh12
Sunflower Seeds1 cupHigh12
Tacos1 small tacoHigh12
General Mills Harmony1 1/4 cupHigh11
General Mills Wheaties Raisin Bran1 cupHigh11
Kellog All-Bran with Extra Fiber1/2 cupHigh11
Kellog Cocoa Krispies3/4 cupHigh11
Pancakes (Homemade)4 cakesHigh11
Spaghetti1 cup cookedHigh11
Uncle Sam1 cupHigh11
White Rice Flour1 cupHigh11
White Rice Flour1 cupHigh11
Cake (Low Fat Only)1 pieceHigh11
Celery, Cooked1 cupHigh10
Chocolate Chip Cookies (store brand)1 cookieHigh10
Collards1 cupHigh10
Kellog Kashi Good Friends3/4 cupHigh10
Quaker Oat Bran1 1/4 cupHigh10
Pancakes (mix)4 cakesHigh10
1 oz or 15 halves
Blueberry Muffins1 muffinHigh9
Other Brands of Cereal
Quaker Cereals
[Source 50)]

What is oxalate diet

Typical diets contain upward of 200 – 300 mg of oxalate. For stone prevention, a reasonable goal is below 100 mg of oxalate daily. An ideal would be about 50 mg daily if that can be accomplished.

To get there, consider the oxalate contents in common serving portions of all of the foods, and make up a plan for yourself. For further help, we suggest discussing your diet with either your physician or a registered dietician.

Existing data on the oxalate content of food are conflicting, making it hard to know what foods can be included in a low oxalate diet. The Harvard School of Public Health maintains a database of foods analyzed for oxalate content 51).

Table 3. Low Oxalate Food Alternatives

Foods High in OxalateLow Oxalate Alternatives
Nut Products (Almonds, Cashews, Peanuts, Pecans, Walnuts)Popcorn
Potato ChipsPopcorn, Graham Crackers, Triscuits, Saltines
Chocolate Chip CookiesOatmeal Cookies, Fig Bars, Popsicles, Pudding, Jello
Rice DreamSoy Milk
Grapefruit, Oranges, TangerinesCantaloupe, Honeydew Melon, Mango, Nectarines
DatesFigs, Raisins
Canned PineappleCanned Peaches, Canned Pears
Dried Figs, Dried PineappleDried Apricots, Apples or Cranberries
Fava, Navy or Refried BeansSoybeans, Mung Beans
SpinachLettuce, Broccoli, Brussels Sprouts
Turnip, YamsYellow Squash
AsparagusBroccoli, Brussels Sprouts, Cauliflower
CollardsKale, Mustard Greens
PotatoesWhite Rice, Macaroni & Cheese
Cream of Wheat, Red River Cereal, Farina Cereal, Corn GritsOatmeal Cereal, Granola Bars
French Toast, PancakesCornbread, Eggs
Clam Chowder, Lentil Soup, Miso SoupChicken Noodle Soup
CheeseburgerHot Dog, Chicken Nuggets
LasagnaMacaroni & Cheese
Peanut ButterApple Butter
Tomato SauceCream Sauce, Olive Oil, Mozzarella Cheese
Blueberry MuffinsOat Bran Muffin, Corn Bread

Table 4. Low oxalate meal plan

Choices Low Oxalate DietServing sizeOxalate Content
Breakfast Meal (Early Morning)
Multi-Grain Cheerios1 cup4.3
Milk (skim or 1%)3/4-1 cup0.5
Cantaloupe1/4 fruit1.3
Apple or Orange Juice(optional)6 oz1.7
Coffee (decaff or reg) with or without cream & sugar1 cup1.0
Total Oxalate8.8
Mid-Morning Snack
Yogurt with Fruit1 cup1.0
Total Oxalate1.0
Whole Wheat Bread2 slices11.4
Tuna Salad3 oz2.5
Lettuce & Tomatoslices1.0
Cheese (american, swiss)2 slices1.2
Mayonnaise1 TBS0.0
Grapes1/2 cup1.0
Chicken Noodle Soup1 cup3.0
Mid-Afternoon Snack
Popcorn (air-popped)1 1/2 cups6.75
Any fresh fish (haddock, cod etc)3 oz1.0
White Rice with stir-fryed Vegetables (mushrooms, onions, broccoli, zucchini)1 cup8.4
Salad (use low oxalate veg)small2.0
Salad Dressing (oil based)2 TBS0.2
Dinner roll1 roll5.9
Diet Lemonade1 cup0.7
Snack (Dessert)
Crackers (Ritz, Wheat etc)5 crackers2.5
Cheddar Cheese5 oz0.5
Red or White Wine4 oz1.0
Total Oxalate58.9

References   [ + ]

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