I’ve seen a lot of negative content lately about oxalates, and I think it’s time to wade into the fray and separate the facts from the fiction.
As a registered dietitian, my main issue with the overarching sentiment that we should all be avoiding oxalates or on a low oxalate diet, is that most oxalate-containing foods are nutrient and fibre packed. It’s super confusing to consumers when they’re told that foods that they’ve always perceived as being ‘healthy’ are now poisoning them and making them sick.
Let’s back up a bit.
What are oxalates?
Oxalates are compounds that are found in many of the foods we eat. Oxalates are formed when oxalic acid binds to minerals in plants. Our bodies can also produce oxalates in the liver using vitamin C and certain amino acids.
Oxalates are often described as being an ‘anti-nutrient,’ because they bind to some minerals and inhibit their absorption in the body. Oxalates are also known to bind to calcium, which in some people, can cause calcium oxalate kidney stones.
Anti-nutrients are a thing, but for most of us, they won’t cause nutritional deficiencies or issues. That hasn’t stopped the wellness industry and random social media personalities from blowing anti-nutrients up into a perceived problem (while selling you the solution, of course).
Dr. Gundry is a great example of someone who has made an entire brand out of demonizing lectins, which are another type of anti-nutrient found in many healthy foods. Phytic acid is another anti-nutrient that’s found in foods like grains and legumes and can bind iron, zinc, magnesium, and calcium.
Lectins and phytic acid are both largely destroyed by cooking and/or sprouting or soaking. This means that they don’t pose a health issue for the majority of people, since we generally cook our grains and legumes before eating them.
Raw kidney beans can actually be lethal, due to a lectin called phytohemagglutinin. The good news is that we don’t eat raw legumes, so this is nothing to worry about.
Oxalates in leafy greens are significantly reduced by cooking, especially by moist cooking methods such as boiling. Yet there are a ton of people advising us to avoid leafy greens like spinach and kale altogether because of oxalates, and this messaging doesn’t take into account that it’s simple to reduce the oxalates in these foods by just cooking them.
That being said, the majority of us don’t have to worry about this, regardless.
What are high oxalate foods?
Foods that are high in oxalates include most leafy greens, nuts, wheat bran, some fruits such as kiwi and raspberries, beans, peas, lentils, cocoa, and tea.
What are some of the claims being made about oxalate?
Oxalates and kidney stones
Oxalates may cause kidney stones in susceptible people – the absorption of oxalates in the gut differs between individuals. It’s recommended that people who have a history of oxalate stones consume oxalate-rich foods with calcium or magnesium-rich ones, so that this binding effect can take place, reducing the amount of oxalate in the body.
Some people who have a predisposition to oxalate stones may need a low oxalate diet; or, they simply may be able to eat these foods in small amounts and spread throughout the day instead of one large amount all at once.
It’s important to note that oxalate in the diet is often already bound to calcium. This creates insoluble calcium, which we do not absorb, and which is excreted in the stool.
Another way the body forms stones is when excess oxalate in the blood are filtered by the kidneys. When there is not adequate fluid flowing through the kidneys, the oxalate can form stones.
Drinking enough fluid every day can help to prevent this.
Oxalate inhibits absorption of other nutrients.
A lot of the social media content around oxalate focuses on oxalate inhibiting absorption of other nutrients. It can be anxiety-producing to hear that certain foods that we always saw as ‘healthy’ can potentially cause nutrient deficiencies, but in most cases, this is all hype and no truth.
The bioavailability of oxalate is different in different foods. For example, collards have a high level of oxalates, but the bioavailability is relatively poor.
Oxalate can bind not only to calcium, but also to iron and zinc, two minerals that can be lacking in plant-based diets. But, if you have a varied diet, eating oxalate-rich foods will probably not have any health consequences.
Individual absorption rates as well as oxalate bioavailability in different foods make a huge difference here, but even so, most of us can eat oxalates without having to think twice about it. If you’re deficient in the above minerals, I’d suggest eating oxalate-rich foods with other, low-oxalate foods, plus a source of calcium.
Oxalates cause osteoporosis and osteopenia.
Since oxalates bind to calcium, eating large amounts of high oxalate foods may decrease bone density over time. This can likely be mitigated by cooking these foods to decrease their oxalate content, eating them with low oxalate foods, and eating oxalate-rich foods with a source of calcium.
if you have osteoporosis, it’s important to be aware of the amount of oxalate-rich foods you consume. Your doctor will be able to tell you if you need a low oxalate diet.
Oxalates are neurotoxic.
This is absolutely not supported by scientific evidence. Anyone who makes this claim is someone you should not be getting your nutrition or health information from.
Oxalates and leaky gut.
Some people believe that oxalates can damage the gut, but there is no mechanism for this whatsoever. While oxalates are absorbed in the gut, it’s the gut lining (and the kidneys) that actually regulate oxalate balance.
As far as oxalates and gut bacteria, healthy bacteria in the large intestine, including one called oxalobacter formigenes, degrade oxalates. Preliminary studies suggest that it’s primarily antibiotics (in particular tetracyclines, macrolides, and fluoroquinolone), that cause decreased levels of oxalobacter in the gut.
Unfortunately, current research doesn’t support the use of oxalobacter probiotics to recolonize the gut with this bacteria.
Oxalates cause painful crystal buildup in the tissues.
Certain practitioners and social media personalities who I don’t necessarily trust (aka Sara Gottfried – who says she has ‘dirty oxalate genes’ – and Dave Asprey (check out my video on IG) are two, unfortunately, there are more) tend to exploit the possibility of excess oxalate forming crystals in body tissues.
It’s unfortunately that ‘Dr Sara’ didn’t give relevant resources to back up many of her claims in this article. I wonder why.
This condition is called oxalosis, and it’s rare. It occurs when people who already have hyperoxaluria (see below) suffer a decrease in kidney function, leading to precipitation of calcium oxalate crystals in organs besides the kidneys.
You probably don’t have oxalosis, by the way. If you think you do, please see a doctor – specifically a nephrologist, not a functional medicine provider (or Dave Asprey).
What is hyperoxaluria?
Primary hyperoxaluria is rare, and is a genetic condition which causes an overproduction of oxalates in the liver. It is not the result of consuming too many oxalates.
Secondary hyperoxaluria occurs when too much oxalate is absorbed through the gut, and is generally associated with malabsorption conditions like IBD, short bowel syndrome, pancreatic insufficiency and other causes fat malabsorption, such as bariatric surgery. This is because fat binds to calcium, leaving the oxalate to be absorbed. Again, under normal circumstances, consuming too many oxalates doesn’t cause secondary hyperoxaluria; it occurs because of the presence of another condition.
Again, hyperoxaluria is rare. Some estimates say the prevalence of primary hyperoxaluria is 1-3 in 1 million people, or around 1000 people in the US. The prevalence on secondary hyperoxaluria is said to be around 250,000 people in the US. Rates of hyperoxaluria in Asia and Europe appear to be higher.
While it is possible to eat so many oxalates that you give yourself hypoxaluria, this seems to be an extreme situation. Most research done around dietary-induced hypoxaluria is actually case studies looking at one individual and their situation.
The case studies I saw included: One person who ate over a cup of peanuts a day (with beer, but that’s low in oxalate) got kidney stones. It wasn’t proven that the peanuts were the source of his oxalate stones. Another had a dietary oxalate intake that was four times higher than the US average. Yet another had kidney stones from chaga tea.
Because they’re small and very specific to one individual, these sorts of studies are not generally applicable to the wider population.
Should you be avoiding oxalates/on a low oxalate diet?
Unless you have an actual medical diagnosis because of which your doctor has told you to reduce oxalates, you’re probably fine to eat them. Even if you do have a condition that impacts your oxalate absorption, you most likely do not have to avoid oxalates altogether, but you definitely should seek advice from your doctor and dietitian.
The overarching recommendation of reputable health professionals and scientific research is that leafy greens, nuts, fruits, beans, and potatoes (white and sweet) are health promoting – high in nutrients, fibre, and antioxidants. Cooking high oxalate foods, eating them with other foods (especially calcium-rich ones), and eating a varied, balanced diet can, in most people, lessen or eliminate any potential nutrient deficiencies from eating these foods.
A low oxalate diet is not going to benefit most healthy people.
It’s also essential to be careful where you get your nutrition information from. People with no scientific training, or who make sweeping nutrition recommendations to everyone, or who use fear to sell you on a diet or a concept, are not reputable or ethical. This unfortunately includes some individuals who have their MD or RD credential. If you’re ever unsure of whether someone is reputable, please look into them before you take their advice.