If you’ve ever searched for the oxalate content of a food, you may have noticed something confusing – the numbers don’t always match.
One list says a vegetable is low. Another says it’s moderate. Occasionally the difference is dramatic, with one list saying “low” and another “very high”.
Why does this happen?
The short answer: not all oxalate testing is the same. And the production of food is not an assembly line function.
Here are the main reasons numbers vary.
1. Testing Methods
In short, not all laboratories measure oxalate the same way.
Older testing methods used strong acids and heat to extract oxalate. Unfortunately, this approach means that test conditions can sometimes cause other natural plant compounds (like vitamin C) to convert into oxalate during testing.
That can make a food look higher in oxalate than it actually is, with a false oxalate signal being sent when it’s not really there.
Modern testing methods are much more precise. They use:
- Enzymes that specifically react with oxalate
- Or chromatography (a technique that separates compounds before measuring them)
These newer methods are more selective and less likely to overestimate.
How can you tell that newer, more reliable testing methods have been used? When the data reported includes soluble versus insoluble oxalate – that’s one key indicator.
2. How food is prepared (or not)
Cooking method matters for all kinds of reasons! For instance, boiling can reduce oxalate because some of it leaches into the cooking water. However, roasting does not remove oxalate. When you roast or bake, all the oxalate remains in the food but you may have a smaller volume of food, due to loss of water – so it may even look higher oxalate per serving!
And of course, any raw food will also have all the oxalate that was present in the original.
So:
- Raw value ≠ Boiled value ≠ Roasted value
If the data lists don’t specify how the food was prepared, the numbers may not be comparable. Your best bet remains clear data with clear descriptions of how the food has been handled.
3. Different Parts of the Plant
Leaves often contain more oxalate than roots. Peels can differ from flesh. Bran can have more oxalate than the starch.
If testing doesn’t specify which part of a plant was analyzed, you don’t know if you have comparable data.
4. Natural Variation in Plants
Plants are living organisms. There are a host of reasons that oxalate levels can vary as a net result:
- Soil
- Growing conditions
- Maturity at harvest
- Storage time
- Variety (different varieties of the same plant may have different oxalate profiles)
These factors usually causes small differences. However, differences in variety in particular may be the difference between a food that can be a regular part of your diet, versus something that is eaten occasionally in small quantities.
5. Copying and Reposting Data
Many oxalate food lists are compiled from older lists. Everyone seems to have their opinion on what data is “valid” versus what data is not. In addition, it’s also possible for errors to be introduced into the data, because of errors made when working with the data.
Over time:
- Data may be copied incorrectly
- Serving sizes may change
- Dry weight may be confused with fresh weight
And what if the original number was incorrect due to a mistake in the lab or a problem with the testing methodology? Once a number appears on a popular list, it can spread widely — even if it wasn’t originally measured under consistent conditions.
What This Means for You
Oxalate numbers are best treated as ranges, not absolutes. I personally work with averages across data points that have been produced by comparable methodologies. When a single data point is wildly different than other data, which seems to cluster around a fairly predictable value, I’m more likely to ignore the wildly divergent data point.
But that said, I do prefer to use an average of clustered data to work out oxalate numbers. Then I also keep in mind that the idea is “pattern over perfection”. It is the pattern of how you eat that matters, as opposed to counting every milligram of oxalate.
Therefore, instead of focusing on a single value (usually from a trusted source), it’s more useful to know:
- Is this food generally low across data sets?
- Generally moderate?
- Generally high?
For most foods, the overall category is much more stable than the exact number. This is why the pattern of how you eat is more important than the specific oxalate numbers (although – like with calories – we use numbers to help us have some idea of what we are taking in.)
Also keep in mind that even a food that may be high oxalate could be enjoyed in “condiment sized” portions. I no longer eat handfuls of nuts for instance – but I will have an ounce of walnuts chopped and sprinkled on a salad. (Personally, I like the crunch and walnuts do have some plant-based omega 3s). I might have 1/4 cup of chopped pecans in a batch of muffins. Small amounts of high oxalate foods used for flavour and texture may be completely doable in your lower oxalate diet.
For many vegetables, especially mild root vegetables and brassicas, modern testing tends to show relatively low oxalate levels as the overall pattern. So if you see some strangely high numbers for something like rutabaga – I’d ignore it.
For more information on foods and their oxalate levels, check out my Patreon group at www.patreon.com/lowoxcoach. You can also find me talking oxalate and related topics on my YouTube channel at www.youtube.com/@lowoxcoach.