Catherine Britell, M.D.
We love our non-starchy vegetables! And for most of us, eating ten or more servings of non-starchy vegetables (concentrating on the dark green ones) per day is the mainstay of a healthy diet. If you have had kidney stones, however, you’ll need to pay attention to the oxalate contained in the vegetables you eat. The good news: this is not difficult, and armed with the right information you can still enjoy plenty of low-oxalate non-starchy vegetables.
People who are overweight or obese need to be aware of the possibility of kidney stones. Compared with persons at or near ideal body weight (BMI = 21-23), obese men (BMI ≥30) have a 33% greater risk for kidney stone formation, while obese women have a 200% greater risk. ( Taylor EN, Stampfer MJ, Curhan GC. Obesity, weight gain, and the risk of kidney stones. JAMA. 2005;293:455-462)
We know that 75% of kidney stones are calcium oxalate stones, and oxalates in the diet can be important causative factors. So, for someone who has had one or more calcium oxalate kidney stones, the general recommendation is limiting oxalates to 50-60 mg/day. For these people, getting 8-10 servings of non-starchy vegetables can present a bit of a challenge. Spinach, chard, beet greens, and many others of those beautiful dark-green non-starchy veggies have large concentrations of oxalates. Also strawberries and most nuts need to be limited or avoided if you must limit oxalates.
However, there are many low-oxalate vegetables — asparagus, broccoli, cauliflower, cucumbers, iceberg and Romaine lettuce, radishes, mushrooms, onions (yellow and white), squash (zucchini, acorn, and yellow), red sweet peppers, turnips (root), water chestnuts and bok choi — that we can eat in quantity and still keep our diet low in oxalate.
Here are some oxalate levels in a few common non-starchy and non-sweet fruits and veggies:
There are many places on the Web to find out the oxalate content of various veggies and fruits.
TIP: According to a study published in Journal of Agricultural and Food Chemistry, “Boiling [vegetables] markedly reduced soluble oxalate content by 30-87%…[and] may be an effective strategy for decreasing oxaluria in individuals predisposed to the development of kidney stones.” (1)
The Bottom Line: People who are prone to kidney stones can build a healthy diet around low-oxalate veggies. (i.e., broccoli is your friend!) Another important dietary consideration for those who develop kidney stones is the need for adequate calcium. (800-1200 mg/day) The Greek yogurt that I love has 200 mg of calcium per serving. Again, broccoili is our buddy here, with almost as much: 180 mg/serving. And Bok Choy with a whopping 180 mg/cup. Celery is also calcium-rich.
And here’s another sweet morsel: Green tea can be beneficial in this regard! It seems that green tea binds to calcium oxalate, creating crystals that break down easily so that they pass out through the urine unnoticed while they are tiny. So, if you have had kidney stones, enjoy your low-oxalate non-starchy vegetables and perhaps a few cups of brewed green tea every day!
(1) Chai W, Liebman M. Effect of different cooking methods on vegetable oxalate content. J Agric Food Chem. 2005 Apr 20;53(8):3027-30. PubMed PMID: 15826055.