Oxalic Acid (aka Oxalates) are naturally-occurring substances found in plants, animals, and in humans. In chemical terms, oxalates belong to a group of molecules called organic acids, and are routinely made by plants, animals, and humans. Our bodies always contain oxalates, and our cells routinely convert other substances into oxalates. For example, vitamin C is one of the substances that our cells routinely convert into oxalates.
In addition to the oxalates that are made inside of our body, oxalates can arrive at our body from the outside, from certain foods that contain them. Oxalates are found in a variety of different foods such as leafy greens, nuts, seeds, most berries, certain fruits, soy and soy products, meat and dairy products.
The main controversy surrounding oxalic acid in food is whether or not they contribute to the formation of kidney stones. About 80% of the kidney stones formed by adults in the U.S.A. are composed of calcium oxalate. Oxalic acid binds with other minerals such as calcium which form a salt known as an oxalate. Oxalic acid interferes with the absorption of calcium in foods because they bind with it, making it unusable by your body.
Oxalates are a controversial subject among nutritionists and health experts especially as it relates to juicing. There have been all kinds of articles floating around the blogsphere lately and since I recently published a post about why I love juicing along with juice recipes, I thought I would take a moment to share some of the opinions regarding consuming oxalate containing foods, specifically as it relates to juicing.
Remember how I mentioned that oxalic acid readily combines with calcium? One argument in favor of juicing oxalate containing fruits and veggies states this: If both oxalic acid and calcium are organic (raw) at the point of combination, the result is beneficial where the oxalic acid helps the digestive assimilation of the calcium. At the same time, this combination helps stimulate the peristaltic functions in our body. It is only when the oxalic acid has become inorganic (cooked or processed), that it forms an interlocking compound with the calcium that destroys the nourishing value of both. This results in a deficiency of calcium that causes decomposition of the bones. Organic oxalic acid is essential for your body and is completely harmless if consumed in organic form. It is the inorganic oxalic acid that causes trouble to your body. This is the reason why when you drink fresh raw spinach juice, your body utilizes 100% of all the minerals that spinach has to offer. But when cooked, the oxalic acid in foods becomes inorganic and may posed some health problems in the long run. 1
So that sounds logical right? No real harm in juicing produce with oxalates right? Not so fast…there is also this viewpoint to consider: Juicing may be more problematic because you are removing parts of the whole food (including fiber), and thus increasing concentrations of other substances. A smoothie, however, contains every part of the whole food, which is the way nature intended food to be consumed, which may minimize oxalate problems. 2
And then I stumbled across this school of thought: A more effective strategy is to ferment foods high in oxalates. This is my favorite strategy of course because you maintain the enzymes in the raw food, add beneficial bacteria to your diet, and increase the B vitamin content …In a 2005 study in Food Microbiology, researchers found that the soluble iron in the homemade vegetable juice in the study increased sixteen times with fermentation. What this means is that if you juice your own vegetable juice with a high iron vegetable like spinach and you ferment it, your body may absorb sixteen times more iron than it would have absorbed had you consumed the juice right out of the juicer. 3
And then finally, a VERY popular train of thought is to boil or steam high oxalate vegetables first, then juice them. The oxalates will literally fall off into the water leaving you with an oxalate free vegetable. But everything I have read leads me to believe that boiling produce will actually cause vitamin and mineral loss.
Sooooo….. I dug deeper and found this:
Cooking has a relatively small impact on the oxalate content of foods. Repeated food chemistry studies have shown no statistically significant lowering of oxalate content following the blanching or boiling of green leafy vegetables. A lowering of oxalate content by about 5-15% is the most you should expect when cooking a high-oxalate food. It does not make sense to overcook oxalate-containing foods in order to reduce their oxalate content. Because many vitamins and minerals are lost from overcooking more quickly than are oxalates, the overcooking of foods (particularly vegetables) will simply result in a far less nutritious diet that is minimally lower in oxalates. 4
Head spinning in confusion? Yeah, mine too.
I'm not sure that there is a right or wrong here. At the end of the day, I personally think it is wise to limit the number of high oxalate containing foods you consume IF you are prone to or already have kidney problems. If you are in good kidney health, then I suspect that rotating high oxalate containing fruits and vegetables in your juices is fairly safe. But again, that is just my opinion. I'm not a doctor.
Here is a little cheat sheet for you:
Fruits high in Oxalates: blueberries, strawberries, currants, lemon, lime, & orange peels, purple grapes, rhubarb, dewberries, figs, gooseberries & kiwi
Vegetables high in oxalates: beets, celery, collards, dandelion greens, eggplant, escarole, green beans, kale, leeks, okra, parsley, parsnips, peppers green, pokeweed, popcorn, potatoes, sweet potatoes, pumpkin, rhubarb, rutabagas, sorrel, spinach, yellow squash, summer squash, Swiss chard, tomato, turnip greens, watercress, yams
Fruits moderate in oxalates: apples, blackberries, raspberries, cranberries, apricots, cherries, grapefruit, green grapes, oranges, peaches, pears, pineapple, plums & prunes.
Vegetable moderate in oxalates: asparagus, artichokes, Brussels sprouts, broccoli, carrots, corn (sweet, white, or yellow), cucumber, garlic, kohlrabi, lettuce, (butter, iceberg), mushrooms, mustard greens, onions, radishes, snow peas, watercress
Fruits low in oxalates: avocado, bing cherries, cantaloupe, lemon & lime juice, mango, coconut, honeydew melon, watermelon, nectarines, papaya & raisins.
Vegetables low in oxalates: acorn squash, all sprouts (alfalfa, broccoli etc.), cabbage, cauliflower, peeled cucumber, red pepper, turnips, zucchini squash.
I don't know about you but a cauliflower, raisin, brussel sprout juice just doesn't float my boat. I think I will continue using my favorite oxalate containing produce in moderation.
For a full list of oxalate containing foods, click here.
Need more information on oxalates? Patty over at Loving Our Guts wrote a great piece on What Are Oxalates. It is worth the read!
Thoughts? Are you at all worried about oxalates as it relates to juicing?