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On PAO scores, How I Built the Calculator and Discrepancies in Oxalate Measurements

As if the prospect of a low-oxalate diet was not enough, individuals who find themselves handling oxalate issues must then attempt to navigate through a quagmire of conflicting information. Are blueberries high or low? What about butternut squash?  Do you need to avoid coffee as well?

All the lists I found were either out of date, inaccurate and incomplete. Some were very accurate but overwhelming with the amount of data. None personalized the data into a relevant number (people absorb oxalates at different rates, see below). Clients told me how these lists were unhelpful and actually caused more confusion. So I built an oxalate calculator from the ground up.

There are five sources of conflict when it comes to the field of oxalates and this is what I considered when building the calculator. These five factors are:

  1. Poor measurement techniques

This is the main reason why there is confusion. Back in the 1990s, oxalates started to become a hot topic when researchers began to realise how much havoc they could cause in the body. Various measurements were made. Years later, the scientific community started to use a blend of capillary electrophoresis and ion chromatography to produce more accurate figures. The new data indicated that, while the initial list still provided a lot of useful data, not all measurements were entirely accurate. The most accurate collection of readings comes from the Trying Low Oxalates group, and this was a major resource in putting together my own calculator.


  1. Shoehorning foods into categories

I get it. Everyone likes it when things are simple. But we have a problem when simplicity comes at the cost of accuracy. These categories are a perfect example. These categories would assign foods a score of ‘low’ if they contained 5mg of oxalates or less (per 100g). A food with 6-15mg would be considered ‘medium’ and 16mg and above would trigger a label of ‘high’.


Sounds fine in theory, but can be very misleading in practise; I’ll use chickpeas to illustrate my point. Chickpeas were traditionally considered to contain 16mg of oxalates for every 100g*. The traditional categories therefore determined that ‘chickpeas are high in oxalates’. Individuals would avoid hummus like the plague, but would happily much on a couple of apples because they contain 3mg per 100mg and are therefore found in the ‘low’ category. The irony here is that apples weigh around 150g and two apples gives you around 11mg of oxalates. A generous serving of hummus will provide significantly less, even if the older measurement was entirely accurate. For this reason, I have not bothered with categories on my oxalate calculator.


*they actually contain about 13mg of oxalates per 100g.


  1. Assessing all foods on the basis of 100g servings

This is more of a follow-on from the example of the lentils vs apples that I’ve outlined above. Comparing 100g of one food versus 100g another has its uses but, in the main, this is a flawed system. Ever eat 100g of potatoes? What about 100g of coffee? Coffee is something that would provide a decent amount of oxalates per 100g, but averages just 1.42mg per cup. That’s not worth a second thought.


The opposite applies to potatoes. 24.2mg for every 100g sounds like they’re worth avoiding, but perhaps OK to eat here and there. Yet a decent-size jacket potato can tip the scales at 600g. That’s 146mg of oxalates in one go. For this reason, I’ve offered a ‘by the gram’ and ‘by the unit’ option when adding items into my calculator.


  1. Natural variability


So you’ve spent hours searching for the oxalate content of an item. You’ve found the data you wanted and you’ve calculated that it fits your ‘oxalate budget’. Great news. But then you find a different brand of the same item has been measured at twice the oxalate content! Is there anything more frustrating?


Unfortunately, there will always be some variability in the oxalate content of the food. Although the range of uniform produce would have us think otherwise, there are huge number of sub-species of each plant (there are 600 different types of apples in the UK alone). Even if we are dealing with the same species, there are further factors to consider; the conditions of the soil, the season it was grown, when it was picked… all of these things can potentially change the amount of oxalates that end up in the final product. For this reason, I have chosen average figures for all foods in my oxalate calculator.


  1. Soluble vs insoluble oxalates

This is a complex subject in its own right, and something I have covered here. However, the basic principle is that soluble oxalates cross the intestinal barrier much more easily; in other words, that they are highly absorbable and the insoluble oxalates are absorbed at much lower rates. This generally rings true, although does not apply across the board; people with impaired digestion are likely to absorb much more of the insoluble form. The presence of soluble and unsoluble oxalates leaves us with two problems, 1) that we have people with different oxalate-processing abilities using the same lists and 2) that these lists invariably quote the total oxalate content only. There is no differentiation between soluble and insoluble, meaning foods who provide only insoluble oxalates are treated as if they are the same as foods whose oxalates are exclusively soluble.


What is needed here is a tool that acknowledges the difference between the two types of oxalates, but also makes this information useful by adapting it for each type of user; those that need not worry so much about the insoluble form, and those that need to be very weary of them. For this reason, I designed my oxalate calculator to both acknowledge the soluble/insoluble content of each food and to produce just one simple figure that is actually relevant to each individual*.


*This set-up means that the figures you get are not scientifically valid in regards to what would be measured in a laboratory, but are much more relevant in regards to how many oxalates may end up inside your body (which is, of course, the only thing we care about when making dietary choices).


Your Personalized Absorbable Oxalate (PAO) Score

I took these considerations into account to determine how much oxalates would end up ‘having a run’ at your intestinal lining, acknowledging that your digestive efficiency may be different to your neighbour’s. That is why the figure produced by the calculator will reflect this. It is your Personalized Absorbable Oxalate Score.

For the five reasons listed above, I think that this oxalate calculator is the only tool on the web that allows individuals to enter a food and get back a figure that is both accurate and applies to them. Just remember not to get too hung up on an exact number because, for the reasons outlined above, being entirely scientifically precise on the numbers is neither practical or important. These numbers are a tool to make better choices and achieve your goals. Doing so is much more important.

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