Maximising Nutrition in a Plant-Based Diet – Spotlight on Oxalates. Having a predominantly plant-based diet offers many health benefits but it also comes with some pitfalls – like the added amount of ‘anti-nutrients’ appearing in your daily diet. Last week we discussed phytates, this week it’s all about oxalates. Best known for their role in kidney stones, you may be surprised to learn that some everyday foods contain moderate to high amounts of oxalates. Vegetarians and vegans who consume greater amounts of vegetables will naturally have a higher intake, so it’s important to know that this may reduce calcium availability, (1) as well as contribute to calcium oxalate kidney stone formation. (2)
All about Oxalates
Oxalates form insoluble salts with minerals, including sodium, potassium, calcium, iron, and magnesium. (3) A diet high in oxalates can bind these essential minerals in the body, while low calcium diets have been linked to increased oxalate absorption. (4) Dietary oxalate is only plant-derived but oxalic acid is also naturally produced within the body endogenously via the liver and also the kidneys. (5) Usually excreted in urine, approximately half of urinary oxalate is derived from the diet and half from endogenous synthesis.(6)
Intake of Oxalates in a Plant-Based Diet
Plant foods with the highest Oxalate content include: (3)(7)
- swiss chard
- sweet potatoes
Spinach contains approximately 658mg oxalates per 100g serving, while amaranth contains a whopping 1090mg per 100g. (4) One long-term study found average daily consumption was slightly above 200mg/day for men, and slightly below this amount for women, where spinach accounted for more than 40% of total oxalate intake. (4) In another study, English diets were calculated to be 70-150 mg/day, with tea appearing to contribute the greatest proportion. (1)
Optimising Oxalates. Factors such as food preparation techniques, calcium intake, endogenous production, and intestinal health (3) all play a role in the impact of oxalates on individuals.
Food preparation techniques – like boiling and steaming are efficient ways to decrease oxalate content. (3) Soaking high oxalate foods and cooking them, rather than consuming foods raw, will help reduce daily intake. (1)
Calcium intake – needs to be adequate to promote excretion. (2) A Naturopath or Nutritionist can assist with dosing advice and prescription of the correct form of calcium.
Endogenous production of oxalate – is influenced by ascorbic acid (vitamin C) intake. (8) Acting as the main dietary precursor for endogenous production, vitamin C requires balance. (2)
Intestinal health – influences absorption and excretion. Oxalobacter formigenes, is an oxalate-degrading Gram-negative bacteria, which appears to colonise the gut of 30–40 % of the population in Western societies. (5) Some types of stool testing can determine whether Oxalobacter is present in the gut.
Some Oxalates are OK!
The occasional consumption of high oxalate foods as part of a nutritious diet doesn’t pose any particular problem. (1) High oxalate foods possess an array of protective, beneficial compounds and these health-giving qualities may outweigh any possible negative effects of oxalate. (3)
Had an “Oh” moment when you are reading this?
If you feel like plant-based eating just got a little lot more complicated, come and chat to us about all things oxalates and otherwise. Food is Medicine so let’s make sure it comes without the unwanted side effects!