There is controversy surrounding the presence of oxalates in foods and whether we should avoid them or how much damage they do to our health. The truth is that, as with all foods, they affect everyone differently and you must decide for yourself if something you eat agrees with you or not through bio-marker tests with a professional or being vigilant by constantly checking in with yourself for symptoms which may be a sign your body is struggling – digestive discomfort, joint pain or persistent chronic symptoms.
We are told that leafy greens, raw cacao, nuts, seeds, beans and tea are all good for us – and they do contain many healthful nutrients but they also contain oxalates and when consumed in high amounts, especially in the absence of calcium, they can cause havoc in the body by forming oxalate crystals which can lead to kidney stones and the lack of calcium can interfere with bone density.
During my years of eating a vegan diet which was high in plants, I regularly started my day with a freshly, cold-pressed green juice made from kale and spinach. I would also eat lots of raw green leafy salads and drink a delicious hot chocolate drink made from raw cacao powder. I was also eating lots of raw nuts which hadn’t been pre-soaked meaning they were high in phytic acid which also inhibits calcium absorption. Mid-afternoon I would stop to have a match green tea and a square of dark chocolate. My oxalate intake was high, calcium low from a vegan diet and I thought I was being healthy! I began to develop some health concerns and as I learned more about the role of anti-nutrients such as oxalates and phytic acid, I realised the way you prepare the food or what you eat it with, can have a huge effect on how it is assimilated in the body.
I am most interested in the knowledge of oxalates binding to calcium which is impactful on my bone health, but I also have a family history of a grandparent with kidney stones and parent with gallstones and subsequent gallbladder removal. Oxalates are shown to bind to calcium and form calcium oxalate crystals, which can contribute to kidney stones in susceptible individuals. Anything I can do to limit my exposure to getting kidney or gallbladder stones is on my to do list!
On top of this, I need the calcium I get from foods to be bio-available for re-building my bones and if the calcium is binding to oxalates from my diet, it will not be available for bone building.
WHAT ARE OXALATES
Oxalates are naturally occurring compounds found in many plant-based foods. It is an inbuilt defence mechanism within plants to preserve its own life and stop insects or pests from eating it. Animals and insects will choose foods which have less oxalates in them.
For humans – oxalates are thought of as anti-nutrients. Oxalates either come from food (Exogenous), or the human body can produce it from metabolising vitamin C (Endogenous).
Anti-nutrients are naturally occurring compounds which interact with the bioavailability of absorbing other nutrients in the body. One such interaction is oxalates binding with calcium. Oxalates can bind with magnesium too. Calcium and magnesium are both important for bone health. Oxalates can effect iron absorption too which is essential for blood health.
Oxalates reduce calcium absorption but eating calcium with the oxalates can actually help limit the damage done during transit – so by eating adequate calcium with the oxalates means that the calcium will bind with them and help to excrete through the digestive system and through stools so that they exit the body with less damage. So, by preparing leafy greens appropriately – such as blanching which helps to remove the oxalates and then adding a grating of calcium rich food such as parmesan cheese, this will do a lot to mitigate the oxalate content and limit absorption into the body.
Calcium oxalate accounts for as much as 80% of kidney stones.
RISK FACTORS FOR OXALATES
Low calcium intake – even if you are not eating calcium and getting it from your diet – your body will be constantly turning over bone and calcium is released into the body and this will bind with the oxalates.
Dehydration – drinking enough fluid will allow the oxalates to be taken through the body more effectively.
High vitamin C intake – oxalates are a bi-product of vitamin C assimilation by the body.
Some people are shown to absorb more oxalates than others and this is thought o be due to the availability of certain microbes in the gut microbiome. People without these microbes absorb more oxalates.
High oxalate consumption can increase inflammation in the body which can be the source of many health problems such as joint issues – arthritis and reducing oxalates has been shown to reduce symptoms for some people.
For more information on this topic – please see Ben Bikman PhD
CAN I LIMIT OXALATES BINDING TO CALCIUM NEEDED FOR MY BONES?
There are some things you can do to reduce the amount of oxalates in your diet and when you do these, you can also limit it further by eating calcium rich foods together with the oxalate rich plant food because this calcium combines with the oxalate to form calcium oxalate and it is carried through the body and excreted, minimising the damage.
IS IT NECESSARY TO STOP EATING ALL FOODS CONTAINING OXALATES?
Some people report to have cured health symptoms by omitting oxalate containing foods from their diet. Maybe these people lack certain gut microbiota to digest or excrete oxalates or maybe they are already suffering with high inflammation in the body making them reject any anti-nutrient containing foods they eat.
Many people can eat foods containing oxalates without any symptoms but issues can arise with the accumulation of oxalates over time. Symptoms such as joint pain, bone density loss or kidney stones are all such health issues which could be related.
It pays to be aware of oxalates and consider how many you are consuming through your diet and how they may be affecting your current and future health.
Therefore, the decision on whether to stop eating oxalate containing foods or just to moderate your intake and be conscious of preparation techniques to minimise them, is something for you to consider.
WHICH FOODS ARE HIGH IN OXALATES?
- Leafy Greens
These are among the highest in oxalates, especially when consumed in large quantities:
- Spinach
- Swiss chard
- Beet greens
- Kale (moderate levels, though lower than spinach)
Some things can determine the amount of oxalates in the leafy greens such as the soil it is grown in and the maturity of the plant.
- Nuts and Seeds
- Almonds
- Cashews
- Peanuts
- Pine nuts
- Sesame seeds
- Fruits
Some fruits have high oxalate content, especially dried fruits:
- Rhubarb (extremely high in oxalates, especially in the leaves, which should never be consumed)
- Starfruit (contains very high oxalate levels)
- Blackberries
- Raspberries
- Figs (especially dried)
- Vegetables
Certain vegetables, especially root vegetables, are high in oxalates:
- Sweet potatoes
- Potatoes (especially the skins)
- Beets (including beetroot and beet greens)
- Okra
- Legumes
- Soy products (like tofu and soybeans)
- Peas (including split peas)
- Chickpeas (moderate levels)
- Lentils (lower levels)
To reduce the oxalate content of legumes:
Soaking: Soak beans and legumes for several hours (preferably overnight) and discard the soaking water before cooking. This can help leach out some of the oxalates.
Cooking: Cooking legumes thoroughly can further reduce the oxalate content, especially if you soak them beforehand.
- Cocoa and Chocolate
Cocoa and chocolate products, especially dark chocolate, are rich in oxalates:
- Dark chocolate
- Cocoa powder
Reducing the amount of oxalates in dark chocolate or raw cacao is very difficult so the only way to mitigate this is by reducing intake or by pairing with a calcium rich food.
- Whole Grains
Some whole grains are moderate sources of oxalates:
- Wheat bran
- Oats
- Rice (brown and wild)
Pre-soaking and discarding the water and then cooking can have an impact on the amount of oxalates remaining.
- Herbs and Spices
Some herbs and spices contain notable oxalate levels, particularly when consumed in large quantities:
- Black pepper
- Turmeric
- Tea
- Black tea
- Green tea
HOW DO OXALATES AND CALCIUM BIND TOGETHER IN THE BODY?
When you eat high-oxalate foods, oxalates can bind to minerals like calcium in your digestive tract to form calcium oxalate. This is typically not absorbed by your body and passes through your intestines for elimination in stool. However, if you eat too many oxalate rich foods or your body is not good at excreting them efficiently, this can cause health problems.
Normally, calcium binds to oxalates in the intestines and prevents them from being absorbed into the bloodstream. However, when oxalate intake is very high or calcium intake is low, oxalates can enter the bloodstream and later bind with calcium in the kidneys, contributing to stone formation.
Also, this binding can reduce calcium absorption, which might contribute to lower calcium levels if dietary calcium intake is inadequate, therefore, it is important to increase your calcium intake to maintain the amount needed by your body for bone formation and heart health.
IF YOU NEED TO REDUCE YOUR OXALATE INTAKE YOU CAN:
- Boil or blanch high-oxalate greens or vegetables (like spinach, kale, Swiss chard or sweet potatoes) to remove some oxalates. Boiling or blanching seems to remove more of the oxalates from food as long as you throw away the liquid and drain. Cooking high oxalate foods in soup for example, means the oxalates just stay in the liquid and you are consuming them. Roasting or steaming does not seem to remove as many oxalates as boiling or blanching.
- Eat a variety of foods so that you’re not relying too heavily on high-oxalate foods.
- Pair high-oxalate foods with calcium-rich foods to help block oxalates from being absorbed into the body.
- Add acidic ingredients: Such as lemon juice or vinegar – this can increase the solubility of the oxalates and promote leaching into the cooking water. Some studies suggest that eating citrus fruits (like lemons and oranges), which contain citric acid, may help reduce the risk of kidney stones. Citric acid can bind with calcium and help prevent calcium oxalate crystal formation.
It’s important to note that while some of these foods are high in oxalates, they also offer numerous health benefits, so moderation and balance are key!
HOW TO INCREASE CALCIUM INTAKE
Here’s a list of calcium-rich foods that can help boost your intake:
Dairy Products:
- Milk (organic)
- Cheese (parmesan)
- Yoghurt (kefir)
- Cottage Cheese
Plant-Based Sources:
- Tofu (calcium-set tofu)
- Fortified plant milks (almond milk, soy milk, oat milk)
- Leafy greens (blanched to reduce oxalates)
- Broccoli
- Chia seeds
- Poppy Seeds
- Almonds
- Tahini or sesame seeds
Fish & Seafood:
- Sardines (with bones)
- Salmon (canned with bones)
Other Sources:
- Figs
- White beans (navy beans, cannellini beans)
Including a variety of these foods in your diet can help you meet your calcium needs.
CONCLUSION
Boiling or blanching greens or pairing the food with a calcium rich food such as yoghurt, cheese, fish with small bones, chis seeds, tahini or almonds are the most effective ways to reduce its oxalate content and ensure you have enough calcium and magnesium available for good bone and heart health. While oxalates aren’t harmful for everyone, those prone to kidney stones or have issues with decreased bone density, may want to limit their intake of high-oxalate foods or use these methods to minimise their impact and increase calcium rich foods in their diet.
DISCLAIMER: This information is for guidance only and is not intended to give professional health advice. If you suspect that you are at risk of oxalate-related issues, please consult your doctor.