Low-oxalate Plant Sources of Protein
Q&A with Bill Harris, M.D.

Q. I became a vegetarian when my then-fiancee (now wife) moved in with me almost 2 years ago. A little over a year later I developed kidney stones for the first time in my life, and I attributed it to having gotten into a habit of eating too much eggplant, which is on the list of foods too high in oxalate to be consumed in quantity by those who suffer from diet-related kidney stones. However, I recently was told about an American Chemical Society article published in August 2001 that indicates soy foods, which had not ever previously been tested for oxalate, had been found to be extremely high in it. That would explain even better why I contracted kidney stones, because I ate a lot of prepackaged soy foods.

A. Calcium oxalate and urate stones are the commonest kinds of kidney stones. Before you hang the rap on oxalate I hope your pathologist has properly identified your stone as oxalate and not urate.

My question now is what other plant sources of protein I should turn to. I have never been overly fond of beans in general, which is partly why I concentrated so heavily on soy foods (that and all the coverage about how good soy is for you!). I enjoy tabouli salad and Thai dishes based on wheat gluten and wonder whether there are similar (presumably low-oxalate) avenues, in addition to the beans I realize I'll have to start eating more of, that I can pursue.

Actually, beans contain purines and since that substance breaks down to uric acid, beans are considered more of a risk for gout and urate renal stones than for oxalate stones although in my experience they cause neither. However, one can get along perfectly well without beans. The basis for a healthy vegan diet should be fresh vegetables, (particularly leafy greens), and fruit, with Calorie needs filled in by raw seeds, nuts, avocados, grains, starches, beans and whatever other whole plant food agrees with you.

However, your question inspired me to a web search and some USDA nutrient data on oxalate. I downloaded it and sorted from high to low oxalate values. Here it is:


Oxalic Acid Content of Selected Vegetables

This table was originally published in Agriculture Handbook No. 8-11, Vegetables and Vegetable Products, 1984.

Vegetable Oxalic acid (g/100 g)

Parsley 1.70
Chives 1.48
Purslane 1.31
Cassava 1.26
Amaranth 1.09
Spinach 0.97
Beet leaves 0.61
Carrot 0.50
Radish 0.48
Collards 0.45
Beans, snap 0.36
Brussels sprouts 0.36
Garlic 0.36
Lettuce 0.33
Watercress 0.31
Sweet potato 0.24
Turnip 0.21
Chicory 0.21
Broccoli 0.19
Celery 0.19
Eggplant 0.19
Cauliflower 0.15
Asparagus 0.13
Endive 0.11
Cabbage 0.10
Tomato 0.05
Pea 0.05
Turnip greens 0.05
Potato 0.05
Onion 0.05
Okra 0.05
Pepper 0.04
Parsnip 0.04
Rutabaga 0.03
Squash 0.02
Kale 0.02
Cucumbers 0.02
Corn, sweet 0.01
Coriander 0.01

It would appear that somebody gave you a bum rap on eggplant. I wasn't able to find acceptable references to the oxalate content of soybean and it doesn't appear in the above list. There was some chatter about tofu being a risk for kidney stone but it seemed to be based on calcium content. While some tofu is soybean soup, precipitated with calcium chloride or sulfate (and thus has a high calcium content), soybeans per se don't make the calcium/Calorie sort until #486 in the USDA SR13 database. Most likely they are a poor source of both calcium and oxalate. Taro leaf, undoubtedly the grand champ for oxalate content, also does not appear in the list.

I was an ER physician for 30 years in Honolulu, surely the kidney stone capital of the world. Our urologists didn't think diet had anything to do with stone formation. However, to the persevering patient I would confide that in my opinion the best way to avoid kidney stones was to avoid organ meats and dairy, thus cutting the risk for both urate and calcium stones respectively, and to drink lots of water, thus diluting whatever bad humors in the urinary tract were still likely to precipitate and form stones.

Here are two references:

Good luck,

-William Harris, M.D.


Urol Int 1982;37(6):394-9

The pattern of urinary stone disease in Leeds and in the United Kingdom in relation to animal protein intake during the period 1960-1980.

Robertson WG, Peacock M

Studies on the occurrence of urinary stone disease in Leeds between 1960 and 1980 show that there was an increase in the number of stones formed during the period 1960-1970, a fall between 1972 and a subsequent rise between 1977 and 1980. The fluctuations in stone incidence were accounted for almost entirely by changes in the number of 'pure' calcium oxalate stones and, to a lesser extent, the number of uric acid stones produced. The incidence patterns of these types of stone closely reflected changes in the consumption of animal protein in the population as a whole during the same period. There were no parallel changes either in the number of stones consisting of a mixture of calcium oxalate and calcium phosphate or in the number of infection stones.

PMID: 7179602, UI: 83094692

Eur Urol 1982;8(6):334-9

Prevalence of urinary stone disease in vegetarians.

Robertson WG, Peacock M, Marshall DH

A study was carried out to determine the effect of a low animal protein diet, such as taken by vegetarians, on the risk of urinary stone disease. A nation-wide survey of vegetarians in the UK showed that the prevalence of urinary stone formation is 40-60% of that predicted for a group of individuals taken from the general population and matched for age, sex and social class with the vegetarians. The findings support the hypothesis that a diet low in animal protein reduces the risk of urinary stone formation.


Here's your American Chemical Society reference. Note that no data is given here on the oxalate content of soybeans, only on the content of processed and usually concentrated soy products :

September 4, 2001

Source: American Chemical Society (http://www.acs.org/)
Date: Posted 8/29/2001

Too Much Soy Could Lead To Kidney Stones

New research indicates that soybeans and soy-based foods, a staple in the diets of many health-conscious consumers, may promote kidney stones in those prone to the painful condition. The finding will be published in the September issue of the Journal of Agricultural and Food Chemistry, a peer-reviewed journal of the American Chemical Society, the world's largest scientific society. The researchers measured nearly a dozen varieties of soybeans for oxalate, a compound that can bind with calcium in the kidney to form kidney stones. They also tested 13 types of soy-based foods, finding enough oxalate in each to potentially cause problems for people with a history of kidney stones, according to Linda Massey, Ph.D., at Washington State University in Spokane. The amount of oxalate in the commercial products easily eclipsed the American Dietetic Association's 10 milligram-per-serving recommendation for patients with kidney stones, with some foods reaching up to 50 times higher than the suggested limit, she noted.

"Under these guidelines, no soybean or soy-[based] food tested could be recommended for consumption by patients with a personal history of kidney stones," she said.

No one had previously examined soy foods for oxalate, thus the researchers are the first to identify oxalate in store-bought products like tofu, soy cheese and soy drinks. Other foods, such as spinach and rhubarb, also contain significant oxalate levels, but are not as widely consumed for their presumed health benefits, Massey said.

During their testing, the researchers found the highest oxalate levels in textured soy protein, which contains up to 638 milligrams of oxalate per 85-gram serving. Soy cheese had the lowest oxalate content, at 16 milligrams per serving. Spinach, measured during previous research, has approximately 543 milligrams per one-cup (2 oz. fresh) serving.

Soy, a natural source of protein, fiber and healthy oils, is used to enhance a myriad of foods, ranging from hamburgers to ice cream. It can be ground into flour and used in a variety of grain products, or formed into chunks and ground like meat. Soy is also being studied for its potential to lower cholesterol, reduce bone loss and prevent breast cancer. The U.S. Food and Drug Administration recently approved a new label on foods containing at least 6.25 grams of soy protein per serving that boasts of a reduced risk of cardiovascular disease.

Oxalate, however, cannot be metabolized by the body and is excreted only through urine, Massey said. The compound has no nutritional value, but binds to calcium to form a mass (kidney stones) that can block the urinary system, she said. Further research is needed to find types of soybeans with less oxalate, or to develop a processing method to remove the compound before it reaches consumers, she added.

No one knows precisely why kidney stones occur in particular individuals. But Massey said high levels of oxalate in the urine increase the risk and those with a family history of the ailment are more likely to suffer from the condition; individuals with a low probability of kidney stones are unlikely to be affected by oxalate in soy-based foods.

More than one million people were diagnosed with kidney stones in the United States in 1996, the most recent available data, according to the National Institutes of Health. Stones can range in size from the diameter of a grain of rice to the width of a golf ball. An estimated 10 percent of the U.S. population, mostly men, will develop a kidney stone at some point in their lives, according to the NIH.


American Chemical Society -- connected to National Cattlemen's Beef Association? http://www.beefnutrition.org/media/press_050201.shtml

Also...see the American Chemical Society website - http://membership.acs.org/C/CentralArizona/014Newsletter.htm

"Cattlemen's Association Barbecue" -- among the "events" listed.

Someone suggested tainted research but neither of these URLs are presently available online.