A study of the effect of dietary habits on absorbable calcium leads one to question the overall impact of calcium oxalate in diet. Found in many plant-based foods, calcium oxalate can concentrate in the kidneys, where it has the potential to crystallize, forming kidney stones. Analysis of kidney stones has shown them to be comprised of up to 75% calcium oxalate.
Dietary Sources Of Calcium Oxalate
The subject of dietary calcium comes up most frequently when discussing methods for the prevention of osteoporosis. While most recommendations for sources of dietary calcium suggest dairy sources, there are several plants that are noted for being good sources of calcium. However, that’s not the whole story.
The primary dietary source of calcium oxalate is plants. A poisonous substance found in many plants, calcium oxalate occurs naturally at high concentrations in many tropical house plants. Capable of producing mouth sores, indigestion, and other digestive problems, experts believe calcium oxalate is produced as a natural defense against insects and herbivores. Consuming small quantities of calcium oxalate has been reported to cause a burning or numbing sensation in the mouth. Larger amounts have been reported to cause much more severe reactions. Also known as beerstone, it can also accumulate on surfaces during the process of brewing beer. Oxalates can also be produced from vitamin C, if excessive amounts of this vitamin are present.
From the standpoint of meeting dietary calcium needs, foods high in oxalates behave similarly to foods high in phytates, in that they form a strong calcium-oxalate complex. That complex is so strong that, although many plant foods have substantial amounts of calcium, most high oxalate foods have very little absorbable calcium available to meet nutritional needs.
The University of Pittsburgh Medical Center groups oxalate-containing foods into three categories. Those foods having a high concentration of oxalates (10-milligrams or more per serving), moderate concentration of oxalates (2-10-milligrams per serving), or low oxalate concentration (less than 2-milligrams per serving). Some of the more common foods in these groups are shown in the following table.
Oxalate In Foods
| Oxalate Rich Foods | Moderate Oxalate Foods | Low Oxalate Foods |
|---|---|---|
| Dark Beer | Draft Beer | Bottled Beer |
| Chocolate | Cranberry Juice | Apple Cider |
| Soy Products | Tomato Juice | Buttermilk |
| Instant Coffee | Yogurt | Green Tea |
| Chocolate Milk | Apples | Lemonade |
| Nuts | Apricots | Avocados |
| Sesame Seeds | Oranges | Bananas |
| Bran | Fresh Peaches | Melons |
| High Fiber Cereal | Fresh Pears | Grapefruit |
| Whole Wheat | Artichoke | Barley |
| Blackberries | Asparagus | White & Wild Rice |
| Blueberries | Broccoli | Cabbage |
| Raspberries | Corn | Cauliflower |
| Rhubarb | Lettuce | Chives |
| Concord Grapes | Onions | Cucumber |
| Beans | Watercress | Mushrooms |
| Potatoes (White & Sweet) | Ginger | Peas |
| Olives | Spongecake | Cinnamon |
| Okra | Whitebread | Ketchup |
| Spinach | Dill | |
| Kiwi Fruit | Nutmeg | |
| Carrots |
Experts also counsel against a diet high in calcium oxalate to help treat kidney stones. Known as hypercalciuria, this treatment can be effective for people who have excessive levels of calcium in the urine. It’s been found that those individuals have a greater tendency to collect calcium oxalate in the kidneys, thereby forming painful kidney stones. There are also people who lack an enzyme required to break down oxalates in the GI tract, which is known as hyperoxaluria. Often times for these people, restricting their consumption of oxalates to less than 50-milligrams per day can dramatically help reduce the occurrence of kidney stones.
The more I learn about the relationship between nutrition, health, and disease prevention, the more fascinating the subject becomes. As subtle as the interaction is between calcium, nutrition, and bone health is, I can’t help but believe there are other interactions at play, or to wonder how many other subtle interactions exist that we haven’t yet ferreted out.
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Nutrition is a very interesting topic. I never knew this about calcium oxalate in our foods. And from your list, I’ve very bummed that beer is at the top of the lists.
The whole beer thing was quite the disappointment to me, too!
All but maybe two of the other foods are not strangers to my diet either, but not the beer…
Many of the high oxalate foods seem to be ones that are really good for you in other ways. Is there any reason to worry about oxalate content if you’re not susceptible to kidney stones? If less than 50 mg/day is good for those who need to worry about kidney stones, what about the rest of us?
Hi Matt!
You’re exactly right about many of the healthier foods also being high in oxalates. It’s mainly a problem for those who are prone to kidney stones, which often times runs in families. Those conditions are discussed above. In cases like that, the recommendation is often to increase water intake and decrease the consumption of foods high in oxalates.