by Teri Buhl
Did you grow up being told to “eat your spinach – it’ll make you strong”? Do you get excited (or weary) about a big bowl of dark, leafy “power greens”? How about rhubarb – love it or hate it? Besides being relatively easy to grow, these plants have another thing in common – oxalic acid – a good or bad thing, depending on your genetics and your gut’s ability to absorb nutrients.
Oxalic Acid, or Oxalate, is an organic compound found in many plants, e.g., leafy greens, vegetables, fruits, cocoa, nuts, and seeds. Your body can produce oxalate or convert Vitamin C into it when metabolized. Once consumed, oxalate binds to minerals to form compounds like calcium oxalate and iron oxalate, which are normally eliminated via the bladder or intestines. In some people, however, high oxalate diets have been linked to kidney stones and other health problems, like reduced calcium absorption.
Sometimes, high amounts of oxalate and calcium can form crystals and lead to kidney stones if urine volume is low. If you are prone to kidney stones, inflammatory bowel disease, or have had gastric bypass surgery, you may want to be tested for oxalate levels and limit your intake to 50 mg per day. You can reduce oxalate consumption by boiling the food item, drinking plenty of water, and making sure you get enough calcium, i.e., 800-1200 mg per day.
One of my personal favorites is sorrel. It’s easy to grow and once established, it starts producing in early spring and continues throughout summer. According to a New Zealand study in 2013, “… [sorrel] should only be consumed in small amounts especially by people who are prone to kidney-stone formation. It is also advisable to prepare sorrel with other calcium-rich foods to reduce the soluble oxalate content, thus reducing the amount of oxalate absorbed into the body. Pesto is an ideal way of preparing sorrel as the serving size is small, so low levels of oxalates will be ingested.”
The study also found that “… incorporating Parmesan cheese in pesto and sour cream in soup also provided calcium, which can effectively reduce the soluble oxalates by conversion to insoluble oxalates…. Soup preparation involved cooking and this may have facilitated the leaching of soluble oxalates from the sorrel leaves, thus allowing the soluble oxalates to combine with calcium, from the sour cream, and form insoluble oxalates, which will not be absorbed from the digestive tract after ingestion.”
In addition, the scientists found that variegated sorrel with a lot of red in the leaves and stems contained more oxalate than green sorrel. This may have implications for rhubarb, chard, and other plants with variegated cultivars. What I really like about this study is that the researchers actually used the following (delicious) recipes to test their theories!
Spicy Sorrel Pesto
80 g large green sorrel leaves
40 g garlic cloves
40 g ground walnuts
8 g chili sauce
1/2 cup (60 g) grated parmesan cheese
10 g olive oil
6 g salt and 2 g pepper
Romanian Sorrel Soup
46 g large green sorrel leaves
50 g chopped onions
6 g olive oil
28 g sour cream
12 g ground rice
1 egg yolk (≈18 g)
6 g salt
For more on oxalic levels in food, please download a copy of the attached chart from St. Joseph’s Healthcare Hamilton. Chart-oxalate-in-food. You may be surprised to discover that even navy beans, baked potatoes, and soy contain a relatively high amount of oxalate.