The Role of Oxalates in Plants and Humans
Before diving into high-oxalate foods to avoid, it helps to understand the broader role of oxalates in plants, our diets, and human health. This context can help us make informed dietary decisions.
Oxalates in Plants
Oxalic acid or oxalates play an integral structural and protective role in many plant species. They support the transport of calcium and other minerals within plants and defend against consumption by binding with calcium to form crystals [20].
This explains why some of the highest oxalate offenders like spinach and rhubarb use oxalates extensively. The more calcium oxalate crystals in a plant, the grittier or more bitter it tends to taste. This deters insects and other predators from consuming the plant.
Oxalate Production in Humans
While plants produce abundant oxalates, our bodies also generate small amounts daily. Oxalic acid is an end product created through metabolism of vitamin C and other molecules in the liver [21].
This internal oxalate production varies widely but averages around 10 to 50 mg per day in adults [22]. Anything we consume in food or supplements gets added onto this baseline load.
Potential Benefits of Oxalates
Despite potential issues in excess, oxalates likely serve some helpful functions in the human body as well. For example, oxalates help regulate calcium absorption. This can prevent excess calcium buildup in tissues [23].
Some early research also suggests oxalates may support probiotic gut bacteria and aid detoxification of heavy metals like lead or mercury [24].
So in moderation, oxalates consumed through a diverse, whole food diet may pose fewer risks and offer benefits. Problems begin arising when excessive oxalate accumulations occur.
Oxalates and Kidney Health
The foremost concern with dietary oxalate overload is impaired kidney function and formation of painful kidney stones. But how common is this issue, and how exactly do excess oxalates damage organ function?
Prevalence of Kidney Stones
Kidney stones currently impact about 1 in 11 people in the United States at some point during their lives [25]. Rates have been rising over recent decades as well.
75-90% of diagnosed kidney stones consist at least partially of calcium oxalate [26]. So the majority of these painful blockages relate to oxalate accumulations binding with calcium.
Oxalates Contributions to Kidney Stones
In the kidneys, higher concentrations of oxalates can bind calcium and slowly accumulate as crystals in kidney tissue. Over time, this builds up, eventually blocking flow through tiny ducts and tubules.
The resulting stone formations cause excruciating pain while also obstructing urine flow. This damages kidney tissue and impairs function. Bacteria may also complicate matters through promoting inflammation and crystal development [27].
Oxalate Kidney Damage Mechanisms
Beyond direct blockages, higher oxalates also appear to damage kidney cell structures and function through other mechanisms as well.
For instance, research finds oxalates increase free radical production while decreasing antioxidant activity. This elevates oxidative stress and inflammation [28].
High oxalates also promote kidney cell programmed death (apoptosis) and interfere with energy production (ATP) [29]. The combined assault ultimately reduces kidney efficiency.
Symptoms and Complications
When oxalates accumulate faster than the kidneys can process them, problematic symptoms like pain, urinary dysfunction, infection risk and stone formation increase.
Warning signs pointing to a kidney stone can include [30]:
- Severe pain in sides, back, groin or abdomen
- Pain radiating to the genitals
- Urinary urgency, frequency and dysfunction
- Blood appearing in the urine
- Nausea/vomiting
- Fever and chills suggesting infection
If left unchecked, recurrent kidney stones or related kidney damage can progress to chronic pain, urinary tract infections, kidney disease, nutrient malabsorption, poor growth and even kidney failure requiring dialysis [31].
Clearly moderating oxalate intake is wise for anyone prone to these complications. Catching issues early through urine testing is key.
Testing For Oxalate Sensitivity
If you suspect oxalate sensitivity based on symptoms or family histories of kidney stones, certain tests can help assess risk and direct nutrition approaches.
Urine and Blood Testing
A 24-hour urine collection test offers the most accurate snapshot of oxalate clearance versus potential accumulation based on excretions [32].
Blood tests help gauge oxalate precursor levels. Combining urine and blood screenings helps determine personal tolerance thresholds and targets [33].
Oxalate Loading Test
For a more definitive sensitivity diagnosis, an oxalate loading test has individuals consume a set high oxalate meal, then monitors urinary oxalate levels over time. Higher post-meal oxalate excretions confirm impaired oxalate processing capabilities [34].
Genetic Testing
Up to 75% of kidney stone risk relates to hereditary factors [35]. So getting screened for genetic predispositions like mutations impacting oxalate production can help assess susceptibilities passed down through families [36].
Armed with this personalized data, you can tailor diet and lifestyle measures to support kidney health.
Hidden Dietary Sources of Oxalates
When scanning nutrition labels, oxalates rarely appear on standard nutrient panels. Yet paying attention to hidden concentrated sources can matter immensely for strict low oxalate diets aiming under 10-50 mg daily.
Beyond the plant foods already highlighted, certain seasonings, grains and beverages sneak in high oxalate loads as well.
High Oxalate Grains
Despite their small size, certain grains carry a mighty oxalate punch. Buckwheat, bran, and bulgur top the list.
Per half cup cooked serving, buckwheat delivers around 50 mg, wheat bran 80 mg, and bulgur around 24 mg of oxalates [37]. Limiting these and opting for safer grains like oats, corn, millet, white rice or quinoa prevents excess oxalates sneaking into meals.
High Oxalate Condiments
Spices and sauces also sometimes supply concentrated hits of oxalates.
Cocoa powder, chili powder, miso, soy sauce, commercial tomato sauce, black pepper and poppy seeds are examples, ranging between 2-7+ mg per teaspoon serving [38].
With savory dishes and baked goods, these little additions can quickly compound, making it important to account for condiments in your total oxalate tally.
High Oxalate Drinks
We already highlighted black tea’s high oxalate content. However, other popular beverages like orange juice, beer, cocoa and dark chocolate milkshakes deliver concentrated oxalates as well.
For example 8 ounces of orange juice carries 7 mg oxalates, black as well as green tea around 5 mg, dark beer around 4 mg and chocolate shakes 5+ mg per serving [39].
Sticking with low-oxalate options like coconut water, pineapple or grape juice, coffee, white milk or water instead prevents excess drinking accumulations.
Oxalate-Containing Supplements
When scanning nutrition labels for oxalates, don’t forget to check supplements as well. Numerous popular options add to oxalate loads.
Green superfood mixes and shakes often contain fruit, cocoa, or veggie blends brimming with offenders like spinach, beet, plum, parsley and kale powders.
Likewise, antioxidant supplements featuring berry extracts, turmeric and high vitamin C doses deliver compounds readily metabolized into oxalates. Even calcium and magnesium forms like calcium citrate and magnesium oxide raise oxalate burdens.
If health conditions demand supplements, opt for low-oxalate friendly options like vitamin D, olive leaf extract or elderberry instead. Always pick whole food sources over high-dose isolates when possible for better tolerance.
Tips for Cooking & Preparing Low-Oxalate Foods
Carefully preparing produce helps reduce oxalates for sensitive individuals while retaining nutrition. Here are some handy kitchen tips for whipping up low-oxalate dishes:
Cooking Methods to Reduce Oxalates
Research shows methods like boiling and blanching help leach water-soluble oxalates out of higher oxalate foods [40]. For example, discarding blanching liquid from spinach can remove over half the oxalate content [41].
Baking, roasting, grilling or microwaving don’t effectively remove oxalates. But combining cooking with discarding liquids does. Draining, blanching or boiling higher oxalate veggies like greens, sweet potatoes or beets before eating is your best bet for lowering content.
Food Preparation Tips
When preparing higher oxalate produce like sweet potatoes or spinach, always include a generous water-to-vegetable ratio and discard the liquid before eating to reduce oxalate loads substantially.
Peeling and deseeding higher oxalate fruits and veggies helps diminish content as well, since oxalates concentrate heavily in outer skins and inner seeds.
Soaking nuts and legumes overnight then draining the water removes some antinutrients like oxalates. Opt for blanched almond flour in baking rather than whole almonds also.
Sample Low-Oxalate Menu
Based on the above tips, here is a sample heart-healthy low-oxalate menu:
Breakfast:
- Egg white omelette with mushrooms, bell peppers and cheese plus citrus fruit
- Oats with bananas, blueberries and almond milk
Lunch:
- Chicken stir fry with white rice, carrots, bok choy and pineapple
Dinner:
- Herb crusted cod with blanched green beans and small baked sweet potato
- Mixed garden salad (lettuce, cucumbers, tomato, chickpeas, citrus vinaigrette) with quinoa berry compote
Snacks/Beverages:
- Greek yogurt with walnuts and blackberries
- Baby carrots and hummus
- Iced hibiscus tea
- Coffee with almond milk
This provides a flavorful low-oxalate day, emphasizing safer fruits, vegetables, whole grains and proteins while limiting higher oxalate offenders.
FAQ on Low-Oxalate Diets
If considering reducing dietary oxalates for kidney health, you likely have plenty of questions on the practicalities. Here are some common low-oxalate diet FAQs:
How difficult is following a low-oxalate diet day to day?
It involves adjustments to remove the very highest offenders like spinach and rhubarb entirely while moderating intake of moderate foods like sweet potatoes and nuts. But you don’t have to eliminate whole food groups or reside on bland restriction. With tasty swaps for produce, wholesome proteins and sensible sweet treats, low-oxalate eating can quickly become second nature.
Do I need to weigh and measure all my foods to tally oxalates?
In the short term, tracking intake using nutrition data for at least a few days helps identify your unique high oxalate triggers and where excess sneaks in. Long term, you likely develop enough awareness of general oxalate counts to intuitively moderate these without needing to constantly count every gram.
How quickly could symptoms potentially improve on a low-oxalate diet?
This varies based on individual factors, but many notice at least some decreases in symptoms like kidney pain within a few weeks as oxalate levels lower and kidney function improves. However sticking to low-oxalate eating consistently for at least 2-3 months helps cement long-term benefits.
Is following a low-oxalate diet expensive?
It does require emphasizing more fresh produce, lean proteins and wholesome ingredients. But when balanced smartly, low-oxalate eating rates very affordable compared to highly restrictive approaches. Strategic meal planning, batch cooking and use of value items helps trim costs substantially.
The Future of Low-Oxalate Diets
Advancements in plant breeding and food processing provide promising possibilities for low-oxalate choices becoming more widely available long-term.
Bioengineering Low-Oxalate Crops
Exciting early research demonstrates the ability to genetically edit greens, grains and legumes to significantly reduce innate oxalate levels [42]. Successfully commercializing such bio-engineered low-oxalate crops would drastically expand food possibilities for sensitive individuals.
Optimizing Cooking for Lower Oxalates
Food technologists also continue investigating methods for optimizing cooking, preparation and processing methods to diminish oxalates in various foods without sacrificing taste or nutrition [43].
Wider application of clever tricks like extended soaking, fermentation, select boiling times and milling processes could greatly expand shelf-stable low-oxalate offerings as well.
The potential future for tastier, more nutritious and affordable low-oxalate food options looks very promising thanks to continual advances in nutritional science and technology.
The Takeaway
Oxalates play a complex role in plants, our diets and human health – sometimes hindering, sometimes helping based on dose and individual variation.
Clearly those diagnosed with oxalate sensitivity related to recurrent kidney stones, pain or impairment require strict avoidance of excessively high oxalate foods accompanied by tailored medical support.
However, for less sensitive individuals merely aiming to promote general health, consuming a predominately whole food diet with abundant produce likely poses little oxalate-related risk. Only mega-dosing green smoothies, high-oxalate veggies multiple times per day and overindulging in other concentrated sources creates potential issues.
Moderation sustains best long-term for nutrition and longevity. But armed with the above insights on oxalate sources, cooking methods and swaps, you can easily craft a savory, sustainable low-oxalate approach if personally required.