Oxalates and your health
If you are switching to a whole-foods plant-based diet, you may come across the idea of anti-nutrients as components in whole, plant-based foods that can have a negative impact on your health. Sounds scary, right?
While anti-nutrients do exist, there is growing understanding that:
For most people, the benefits of the foods they are in out-weigh any negative effect
For most people, the negative effects are not as profound or common as initially thought
Some anti-nutrients actually convey health benefits!
Some of the commonly listed anti-nutrients are lectins, phytates, tannins, saponins, glucosinates and oxalates. In this post I will discuss oxalates, saving the rest for later ;)
Oxalates are found in many plants where they serve as a defence mechanism and for regulating calcium levels. Oxalates are particularly high in beetroot greens, spinach, swiss chard, stewed rhubarb, rice bran, buckwheat groats, almonds and dark chocolate.
Oxalates have a bad rap for two reasons:
In your gut, oxalates will bind the positively charged minerals such as calcium, magnesium and iron. The issue here is that this means there will be fewer of these minerals available for absorption therefore possibly contributing to a mineral deficiency.
If absorbed, oxalates travel to your kidneys where they are excreted. This is an issue as 80% of kidney stones are calcium oxalate crystals, so the thinking goes that if you have a high oxalate diet you may be at greater risk of kidney stones.
So let me discuss both of these potential issues with oxalates, and explain why you might not want to ban all oxalate rich foods from your diet just yet.
Starting with contributing to mineral deficiency. In a balanced diet with a wide variety of foods eaten, this actually does not seem to be so much of a problem. The oxalates only reduce availability of the minerals in the food in which they are present, so you could for example eat a whole bunch of spinach (oxalate rich food) alongside broccoli (calcium rich food) and still absorb as much calcium from the broccoli as you would minus the spinach. So for most people eating a varied diet, this is not something to worry about.
But what about kidney stones? First off, it is important to understand that oxalate-rich plant-based foods are not your only source of oxalates. Your body actually makes oxalates as well (they come from the break-down of vitamin C and certain amino acids - i.e. protein). I am definitely not saying you should reduce your intake of vitamin C, or protein necessarily though! These are both important components of your diet. But it is interesting that vitamin C breakdown to oxalates is increased in the presence of cadmium which is found in cigarette smoke - so maybe quit smoking? - and animal protein has an acid forming effect in the kidneys which increases the risk of stone formation - so plant-based proteins are defo better.
Studies looking into the link between oxalate-rich foods and kidney stones actually found that people suffering with kidney stones do not eat more oxalate-rich foods than those without kidney stones (1), and people eating more fruit and vegetables overall have a lower risk of kidney stones (2) possibly due to the alkalising effect of fruit and veg.
So should we be concerned about oxalates at all? Well that depends… for most of us eating a varied diet (so not eating high oxalate foods day in and day out), we don’t need to worry. But if you are predisposed to kidney stones (i.e. family history or have high oxalate levels in your blood or urine) then you may want to be cautious. For example, some people are super-absorbers of oxalates, meaning they absorb more than would be considered normal. You may also want to be cautious if you suffer from gout, as iron oxalate crystals can be the basis upon which the sodium urate crystals associated with gout can accumulate. Also, those with Rheumatoid Arthritis may want to be cautious with oxalates.
If you are at high risk of kidney stones, or if you have been advised by your physician to reduce oxalates in your diet, here is a good website with a comprehensive list of oxalate content in many foods: https://kidneystones.uchicago.edu/how-to-eat-a-low-oxalate-diet/
And if you are a dedicated juicer, keep in mind rotating your greens. There have been a handful of cases of kidney failure after extreme juicing of oxalate-rich greens (for example see reference 3), so if you are drinking loads of green juices/smoothies you may want to make sure you are varying your ingredients so they are not always oxalate rich. Kale, watercress, romaine lettuce and bok choy are examples of low oxalate greens you could swap into the place of the high oxalate spinach, swiss chard and beet greens.
I hope that helps clarify oxalates!
Nourish yourself every day :)
Fabia
References
Turney BW, Appleby PN, Reynard JM, Noble JG, Key TJ, Allen NE. Diet and risk of kidney stones in the Oxford cohort of the European Prospective Investigation into Cancer and Nutrition (EPIC). Eur J Epidemiol. 2014 May;29(5):363-9.
Meschi T, Maggiore U, Fiaccadori E, Schianchi T, Bosi S, Adorni G, Ridolo E, Guerra A, Allegri F, Novarini A, Borghi L. The effect of fruits and vegetables on urinary stone risk factors. Kidney Int. 2004 Dec;66(6):2402-10.
Makkapati S, D'Agati VD, Balsam L. "Green Smoothie Cleanse" Causing Acute Oxalate Nephropathy. Am J Kidney Dis. 2018 Feb;71(2):281-286.
