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

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 ³¹. In a study ³², 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% ³¹. Other observational studies have shown an inverse relation between dietary calcium and the risk for incident kidney stones ³³, ³⁴ 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 ³⁵. Magnesium intake may also decrease urinary oxalate in a similar manner ³⁶, ³⁷.

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 ³⁸, ³⁹. 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 ²⁰.

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 ⁴⁰, Averrhoa bilimbi (commonly known as bilimbi or cucumber tree) ²¹, celery, carrots, parsley, beets, and spinach ⁴¹.

Even though those food products are ubiquitous in many diets, there have been few reports of renal parenchymal disease secondary to dietary hyperoxaluria ⁴². Bakul et al have described a case series of 10 patients who developed acute renal failure after consumption of A. bilimbi fruit juice ²¹. 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

Table 1. Foods that contribute to oxalate

Food	%	Food	%	Food	%
Cooked spinach	23.1	Cooked spinach	25.8	Cooked spinach	22.0
Raw spinach	17.3	Raw spinach	18.4	Raw spinach	20.3
Potatoes (whole)	10.2	Potatoes (whole)	11.1	Potatoes (whole)	9.9
Cold cereal	4.4	Cold cereal	4.3	Cold cereal	3.8
Oranges	2.9	Oranges	2.5	French fries	2.5
French fries	1.9	Coffee	1.7	Oranges	2.0
Mixed nuts	1.7	Cooked carrots	1.7	Pasta	2.0
Navy beans (canned)	1.7	Tea	1.6	Pasta sauce	1.9
Cookies	1.6	Cookies	1.5	English muffins	1.7
Peanuts	1.6	Pasta sauce	1.4	Coffee	1.7

Note ⁴³: Spinach has 794 mg oxalate/100 g; Potato has 24.7 mg oxalate/100 g;

[Source ⁴⁴]

Table 2. Oxalate content of foods

Food Item	Serving size		Oxalate Category		Oxalate Value
Spinach, cooked	1/2 cup		Very High		755
Spinach, raw	1 cup		Very High		656
Rhubarb	1/2 cup		Very High		541
Rice Bran	1 cup		Very High		281
Buckwheat Groats	1 cup cooked		Very High		133
Almonds	1 oz or 22 kernels		Very High		122
Miso Soup	1 cup		Very High		111
Wheat Berries	1 cup cooked		Very High		98
Corn Grits	1 cup		Very High		97
Corn Grits	1 cup		Very High		97
Baked Potato with Skin	1 medium		Very High		97
Soy Flour	1 cup		Very High		94
Bulgur, cooked	1 cup		Very High		86
Navy Beans	1/2 cup		Very High		76
Beets	1/2 cup		Very High		76
Cocoa Powder	4 tsp		Very High		67
Hot Chocolate (homemade)	1 cup		Very High		65
Brown Rice Flour	1 cup		Very High		65
Brown Rice Flour	1 cup		Very High		65
Cornmeal	1 cup		Very High		64
Cornmeal	1 cup		Very High		64
Millet, cooked	1 cup		Very High		62
Okra	1/2 cup		Very High		57
Bran Flakes with Raisins, Single Brand	1 cup		Very High		57
Post Original Shredded Wheat & Bran	1 1/4 cup		Very High		53
French Fries	4 oz		Very High		51
French Fries (homemade or fast food)	4 oz or 1/2 cup		Very High		51
Cashews	1 oz or 18 kernels		Very High		49
Raspberries	1 cup		Very High		48
Soy Beans	1/2 Cup		Very High	***	48
Nabisco Honey Nut Shredded Wheat Bite Size	1 cup		Very High		47
Kellog Raisin Bran	1 cup		Very High		46
Spoonsize Shredded Wheat	1 cup		Very High		45
Nabisco Shredded Wheat	2 biscuits		Very High		42
Stevia	1 tsp		Very High	***	42
Post Fruit & Fiber Dates, Raisins & Walnuts	1 cup		Very High		41
Raisin Squares Mini-Wheats	3/4 cup		Very High		41
Barley Flour	1/2 Cup		Very High	***	41
Miso	1 cup		Very High		40
Miso	1 cup		Very High		40
Yams	1/2 cup, cubed		Very High		40
Bagel NY Style	1 Bagel		Very High	***	40
Lentil Soup	1 cup		Very High		39
Mixed Nuts (with Peanuts)	1 oz		Very High		39
Chocolate Syrup	2 Tbs		Very High		38
Chocolate Syrup	2 Tbs		Very High		38
Candies with Nuts (ex Snickers)	2 oz		Very High		38
Candies with Nuts (ex Snickers)	2 oz		Very High		38
Pancakes (dry mix)	4 pancakes		Very High		37
General Mills Multi-Bran Chex	1 cup		Very High		36
Post 40% Bran	3/4 cup		Very High		36
Stuffing	1 cup		Very High		36
Kellog Special K Low Carb	1/2 Cup		Very High	***	35
Post Cranberry Almond Crunch (Morning Traditions)	1 cup		Very High		35
Bamboo Shoots	1 cup		Very High		35
Kellog Complete Wheat Bran	3/4 cup		Very High		34
General Mills Total Raisin Bran	1 cup		Very High		31
Rutabaga	1/2 cup mashed		Very High		31
Walnuts	1 cup or 7 nuts		Very High		31
Brownies	1 oz or 1/2 brownie		Very High		31
Dried Pineapples	1/2 cup		Very High		30
Turnip	1/2 cup mashed		Very High		30
Mashed Potatoes	1 cup		Very High		29
Orange	1 fruit		Very High		29
Wheat Flour, Whole Grain	1 cup		Very High		29
Wheat Flour, Whole Grain	1 cup		Very High		29
Fudge Sauce	2 Tbs		Very High		28
Fudge Sauce	2 Tbs		Very High		28
Kellog Frosted Mini-Wheats	1 cup		Very High		28
Sweet Potatoes	1 cup		Very High		28
Kellog Raisin Bran Crunch	1 cup		Very High		27
Peanuts	1 oz		Very High		27
Soy Protein Isolate	1 oz		Very High		27
Carrot Juice	1 cup		Very High		27
Kellog All-Bran Original	1/2 cup		Very High		26
Post 100% Bran	1/3 cup		Very High		25
Post Banana Nut Crunch	1 cup		Very High		25
Chili with Beans	1 cup		Very High		24
Dates	1 date		Very High		24
Dried Figs	5 pieces/fruits		Very High		24
General Mills Oatmeal Crisp with Almonds	1 cup		Very High		24
General Mills Raisin Nut Bran	1 cup		Very High		24
Veggie Burger	1 pattie		Very High		24
Brown Rice, cooked	1 cup		Very High		24
General Mills Honey Nut Clusters	1 cup		Very High		23
Lasagna	1 serving		Very High		23
Lasagna with meat	1 serving		Very High		23
Pancakes (Homemade)	4 pancakes		Very High		22
Potato Chips	1 oz		Very High		21
Potato Chips	1 oz		Very High		21
Fava Beans	1/2 cup		Very High		20
Kellog All-Bran Buds	1/2 cup		Very High		20
Kellog Mueslix Apple & Almond Crunch	2/3 cup		Very High		20
Soy Milk	1 Cup		Very High	***	20
Celery Raw	1/2 Cup		Very High	***	19
Avocados	1 fruit		Very High		19
Cream of Wheat	1 cup		Very High		18
Olives	approx 10 olives		Very High		18
Post Great Grains Crunch Pecan	2/3 cup		Very High		18
V8 Juice	1 cup		Very High		18
General Mills Basic 4	1 cup		Very High		17
Mueslix	2/3 cup		Very High		17
Post Great Grains Raisin, Dates & Pecans	2/3 cup		Very High		17
Potato Salad	1/3 cup		Very High		17
Pumpkin Seeds	1 cup, cooked		Very High		17
Tomato Sauce	1/2 cup		Very High		17
All-Purpose Flour	1 cup		Very High		17
All-Purpose Flour	1 cup		Very High		17
Brussel Sprouts Raw	1/2 Cup		Very High	***	17
Burritos with beans	1 burrito		Very High		17
Farina Cereal	1 cup		Very High		16
Kellog Low Fat Granola with Raisins	2/3 cup		Very High		16
Kiwi	1 fruit		Very High		16
Peanut Butter Reduced Fat	1 Tbs		Very High		16
Refried Beans	1/2 cup		Very High		16
Tahini	1 Tbs		Very High		16
Burritos with beans & meat	1 burrito		Very High		16
Cake (homemade)	1 piece		Very High		16
Couscous	1 cup		Very High		15
Kellog Cracklin’ Oat Bran	3/4 cup		Very High		15
Kellog Smart Start	1 cup		Very High		15
Lemonade (frozen from concentrate)	8 oz		Very High		15
Quaker Low Fat 100% Natural Granola with Raisins	3/4 cup		Very High		15
Parsnip	1/2 cup		Very High		15
Red Kidney Beans	1/2 cup		Very High		15
Trail Mix	1 oz		Very High		15
Cake (store brand)	1 piece		Very High		15
Carrots, raw	1/2 Cup		Very High	***	15
Danish Pastry Homemade	1 pastry		Very High		14
Kellog Kashi Go Lean	3/4 cup		Very High		14
Pistachios	1 oz or 48 kernels		Very High		14
Post Grape Nuts	1/2 cup		Very High		14
Tea, Brewed	1 cup		Very High		14
Tomato Juice	1 cup		Very High		14
Cheeseburger with bun	1 burger & bun		Very High		13
Clam Chowder	1 cup		Very High		13
Enchilada with Cheese & beef	1 enchilada		Very High		13
Enchilada with Chicken	1 enchilada		Very High		13
French Toast	2 slices		Very High		13
French Toast	2 slices		Very High		13
General Mills Fiber One	1/2 cup		Very High		13
General Mills Nature Valley Cinnimon & Raisins Granola	3/4 cup		Very High		13
General Mills Oatmeal Raisin Crisp	1 cup		Very High		13
Kellog Just Right Fruit & Nut	1 cup		Very High		13
Kellog Puffed Kashi	1 cup		Very High		13
Nachos with Cheese	6-8 chips		Very High		13
Peanut Butter	1 Tbs		Very High		13
Pizza with Cheese	2 slices		Very High		13
Red River Cereal	1/4 cup		Very High		13
Rice Dream	1 cup		Very High		13
Sweet Rolls Low Fat	1 pastry		Very High		13
Tofu	3.5oz		Very High		13
Quaker 100% Natural Granola Oats & Honey	1/2 cup		Very High		13
English Muffin Whole Wheat	1 muffin		High		12
English Muffins Whole Wheat ONLY	1 muffin		High		12
Grapefruit	1/2 fruit		High		12
Grilled Cheese Sandwich	1 sandwich		High		12
Sunflower Seeds	1 cup		High		12
Tacos	1 small taco		High		12
General Mills Harmony	1 1/4 cup		High		11
General Mills Wheaties Raisin Bran	1 cup		High		11
Kellog All-Bran with Extra Fiber	1/2 cup		High		11
Kellog Cocoa Krispies	3/4 cup		High		11
Pancakes (Homemade)	4 cakes		High		11
Spaghetti	1 cup cooked		High		11
Uncle Sam	1 cup		High		11
White Rice Flour	1 cup		High		11
White Rice Flour	1 cup		High		11
Cake (Low Fat Only)	1 piece		High		11
Celery, Cooked	1 cup		High		10
Chocolate Chip Cookies (store brand)	1 cookie		High		10
Collards	1 cup		High		10
Kellog Kashi Good Friends	3/4 cup		High		10
Quaker Oat Bran	1 1/4 cup		High		10
Pancakes (mix)	4 cakes		High		10
Pecans	1 oz or 15 halves		High		10
Blueberry Muffins	1 muffin		High		9
Other Brands of Cereal
Quaker Cereals

[Source ⁴⁵]

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 ⁴⁶.

Table 3. Low Oxalate Food Alternatives

Foods High in Oxalate	Low Oxalate Alternatives
Nut Products (Almonds, Cashews, Peanuts, Pecans, Walnuts)	Popcorn
Potato Chips	Popcorn, Graham Crackers, Triscuits, Saltines
Chocolate Chip Cookies	Oatmeal Cookies, Fig Bars, Popsicles, Pudding, Jello
Rice Dream	Soy Milk
Grapefruit, Oranges, Tangerines	Cantaloupe, Honeydew Melon, Mango, Nectarines
Dates	Figs, Raisins
Canned Pineapple	Canned Peaches, Canned Pears
Dried Figs, Dried Pineapple	Dried Apricots, Apples or Cranberries
Fava, Navy or Refried Beans	Soybeans, Mung Beans
Spinach	Lettuce, Broccoli, Brussels Sprouts
Turnip, Yams	Yellow Squash
Asparagus	Broccoli, Brussels Sprouts, Cauliflower
Collards	Kale, Mustard Greens
Potatoes	White Rice, Macaroni & Cheese
Cream of Wheat, Red River Cereal, Farina Cereal, Corn Grits	Oatmeal Cereal, Granola Bars
French Toast, Pancakes	Cornbread, Eggs
Clam Chowder, Lentil Soup, Miso Soup	Chicken Noodle Soup
Cheeseburger	Hot Dog, Chicken Nuggets
Lasagna	Macaroni & Cheese
Peanut Butter	Apple Butter
Tomato Sauce	Cream Sauce, Olive Oil, Mozzarella Cheese
Blueberry Muffins	Oat Bran Muffin, Corn Bread

Table 4. Low oxalate meal plan

Choices Low Oxalate Diet	Serving size	Oxalate Content
Breakfast Meal (Early Morning)
Multi-Grain Cheerios	1 cup	4.3
Milk (skim or 1%)	3/4-1 cup	0.5
Cantaloupe	1/4 fruit	1.3
Apple or Orange Juice(optional)	6 oz	1.7
Coffee (decaff or reg) with or without cream & sugar	1 cup	1.0
Total Oxalate		8.8
Mid-Morning Snack
Yogurt with Fruit	1 cup	1.0
Total Oxalate		1.0
Lunch
Whole Wheat Bread	2 slices	11.4
Tuna Salad	3 oz	2.5
Lettuce & Tomato	slices	1.0
Cheese (american, swiss)	2 slices	1.2
Mayonnaise	1 TBS	0.0
Grapes	1/2 cup	1.0
Chicken Noodle Soup	1 cup	3.0
Total		20.1
Mid-Afternoon Snack
Popcorn (air-popped)	1 1/2 cups	6.75
Total		6.75
Dinner
Any fresh fish (haddock, cod etc)	3 oz	1.0
White Rice with stir-fryed Vegetables (mushrooms, onions, broccoli, zucchini)	1 cup	8.4
Salad (use low oxalate veg)	small	2.0
Salad Dressing (oil based)	2 TBS	0.2
Dinner roll	1 roll	5.9
Diet Lemonade	1 cup	0.7
Total		18.2
Snack (Dessert)
Crackers (Ritz, Wheat etc)	5 crackers	2.5
Cheddar Cheese	5 oz	0.5
Red or White Wine	4 oz	1.0
Total		4.0
Total Oxalate		58.9

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