If you regularly include foods like spinach, chocolate and potatoes in your diet, then you’re consuming oxalic acid (aka oxalate) whether you’re aware of it or not. While this compound is found in many healthy foods — such as vegetables, fruits, nuts and some whole grains — it can lead to problems in certain people when eaten in high amounts.
The main concern with consuming too much of this compound is the risk for developing kidney stones, since they are most often formed from the buildup of oxalates and calcium. If you’ve dealt with kidney stones in the past or your doctor has told you that you’re at risk for developing them in the future, it can be helpful to follow a low-oxalate diet.
What Is Oxalic Acid?
The definition of oxalic acid (also known as ethanedioic acid) is “a poisonous strong acid (COOH) that occurs in various plants (such as spinach) as oxalates and is used especially as a bleaching or cleaning agent and as a chemical intermediate.”
Oxalic acid is technically known as ethanedioic acid and has the formula H2C2O4. It’s usually made in a lab (commercially) using a combination of sugar and nitric acid.
When purified and isolated, it appears as a white crystal substance.
Is oxalic acid a strong acid?
Yes it is — so much so that it’s corrosive. Its uses include making a number of sterilizing products intended to clean surfaces, water, metals and fabrics.
What is the meaning of oxalate, and how is it different than oxalic acid? Oxalates are naturally occurring compounds found in many different types of vegetables and plant foods.
Oxalate is present in both certain plants and the human body, since it’s ingested in small amounts when people consume commonly eaten foods.
Once consumed, what is oxalic acid used for in the body?
Oxalates are not digestible, so in a healthy digestive tract they are metabolized by probiotic gut bacteria and then excreted as a waste product. We normally get rid of oxalates after they pass through the digestive system and end up in our stool or urine.
However, excess amounts can still accumulate, especially in the kidneys — where they can cause the buildup of crystals.
Side Effects and Concerns
Why is oxalic acid harmful to humans?
It’s dangerous to ingest large amounts of oxalic acid, such as from certain foods or drugs, and also to apply it to your skin topically because it has antinutrient and corrosive properties (sometimes described as”bleach-like effects”).
In fact, this is the exact reason that it’s isolated and then used in industrial cleaning.
What are the symptoms of high oxalates?
The side effects of oxalic acid/oxalates in excess amounts can include:
- Kidney stones — when crystals combine together to form a kidney stone, they can stick to the lining of the kidneys and cause lots of pain
- Bladder problems
- Worsened fibromyalgia symptoms (muscle pains, chronic fatigue, brain fog, hormone imbalance, insomnia and headaches)
- Candida overgrowth
- Vulvodynia (chronic inflammation and pain for women throughout the female genitalia)
- Potentially higher risk for development of certain cancers, including breast cancer
The Connection Between Oxalates and Kidney Stones
Oxalate crystals can form in the body over time, and in some people this can cause kidney stones to develop, potentially as well as other complications. Kidney stones are pieces of stone-like material that form on the walls of the kidney.
Calcium oxalate kidney stones are the most common type of kidney stone. This is why people at high risk for kidney stones are told to lower their oxalate intake from plants.
Calcium oxalate stones can also negatively affect the bladder.
Can too much ever be a serious concern? Can oxalic acid kill you?
Severe oxalic acid poisoning is rare. The most serious side effects that can occur include kidney failure and gastrointestinal disorders.
These complications may occur over time or in situations such as following surgery. The most common cause of poisoning from this chemical is accidental ingestion of cleaning products or other chemicals, such as antifreeze or bleach.
High intake also interferes with absorption and use of essential minerals in the body, including magnesium and calcium.
Oxalates bind to calcium, such as in the intestines after you eat a food that provides both calcium and oxalates (lik vegetables.). This means the body absorbs less calcium.
Who is at risk for oxalate side effects?
- People who eat lots of high oxalate foods.
- Those who don’t consume lots of calcium foods, since low calcium intake allows for more unbinded oxalate to reach the kidneys. Eating calcium helps reduce the amount of oxalate being absorbed by your body.
- People who consume high amounts of vitamin C (more than 1,000 milligrams per day), particularly from supplements. Oxalic acid is released when vitamin C is broken down, increasing levels in the body.
- Anyone who uses antibiotics long term or frequently, since these reduce healthy bacteria in the gut that help balance oxalate levels.
- Those with a history of digestive diseases that hinder functions of healthy gut bacteria, such as inflammatory bowel disease, allergies or intestinal permeability, also known as leaky gut.
- Rarely, a genetic disorder known as primary hyperoxaluria can cause the body to overproduce oxalates.
Oxalic acid occurs in lots of different foods — some in tiny amounts and a few foods in larger amounts.
A food is considered “high in oxalates” when it has more than 10 milligrams per serving. It’s low in oxalates if it has less than two milligrams.
Those that fall somewhere in the middle are “medium oxalate foods.”
Which foods contain oxalates? The foods highest in oxalic acid are:
- Dark leafy greens, like spinach, escarole, beet greens, kale, collards and Swiss chard
- Sweet potato
- Zucchini/summer squash
- Peppers (chili and green)
- Fruits, including blackberries, blueberries, raspberries, kiwis, tangerines and figs
- Nuts and seeds, including almonds, cashews and peanuts
- Tahini/sesame seeds
- Legumes and soy products, including miso, tofu, soy milk and soy yogurt, baked beans, green beans, and kidney beans
- Some grains, such as bulgur, corn grits, bran flakes, wheat germ, whole wheat bread, amaranth, buckwheat and quinoa
- Cocoa/chocolate/chocolate milk
- Black tea
- Instant coffee
- Dark beers
- Brewed coffee (medium oxalate, OK for most in moderation)
- Carrot, tomato and orange juice (medium oxalate)
- Apples, oranges, prunes, pears, pineapple, peaches, apricots (medium oxalate)
- Artichoke, fennel, canned peas, asparagus, tomato, lima beans, brussel sprouts, mustard greens, turnips, onions, parsnips, corn (all medium oxalate)
Oxalates have uses in certain industries, including cleaning/sterilizing, waste management and production of medications. Here are some of the purposes it serves:
- Serving as an ingredient in various cleaning products, such as bleaches and detergents
- Cleaning and sterilizing, including household items like counters, bathtubs and kitchen sinks
- Removing rust and stains
- Bleaching fabrics before color is added
- Purifying or diluting certain chemicals that are used in medicine
- Waste water applications
- Mineral processing
When it’s used for these purposes, it’s important to be cautious in order to prevent skin reactions, side effects and toxicity.
Some important steps to take in order to protect yourself include:
- wearing protective glasses, gloves and proper clothing
- keeping products away from children and pets
- making sure to keep these products away from your eyes and never swallowing them
These help to limit the risk for high amounts of exposure, both topically and internally.
How to Follow a Low-Oxalate Diet
If you’re looking to learn how to prevent kidney stones, one of the first things to do is adopt a low-oxalate diet. This is especially important if you’re susceptible to kidney stones.
A low oxalate diet is one that provides 40 to 50 milligrams of oxalates per day or less. Follow diet for at least three to six weeks to see if your symptoms improve.
Here’s how to follow a low-oxalate diet:
1. Avoid High-Oxalate Foods (see the high oxalate food list above)
2. Eat Mostly From This Low-Oxalate Foods List (with moderate amounts of medium oxalate foods listed above):
- Water chestnut
- Raisins (1/4 cup)
- Meat, poultry and fish
- Milk and cheese
- Herbal teas
- Most herbs and spices
- Honey, mustard, vinegar and ketchup
- Apple cider vinegar
3. Increase Your Intake of Calcium Foods
Oxalate and calcium bind together, which can help prevent them from forming kidney stones. So when you do consume oxalate foods, try also having more calcium foods too — such as sardines, yogurt, kefir, cheese and almonds.
Aim for two to three servings of calcium foods daily.
4. Drink Plenty of Water
Water can help to flush materials out of the kidneys. Aim for eight to 16 glasses of water/fluids per day (eight ounces each).
5. Don’t Overconsume Protein
To protect your kidneys, aim to reduce your sodium intake (or follow a low-sodium diet plan) and eat a moderate-protein diet. Most adults should aim to get between 10 percent to 20 percent of daily calories from protein foods.
6. Cook Oxalate Foods
Does cooking reduce oxalates?
Yes, boiling and steaming can help reduce oxalate levels in some foods, such as greens and other veggies. Try boiling vegetables for six to 10 minutes rather than eating them raw or steaming them for several minutes until soft.
Does soaking reduce oxalates?
Yes, soaking grains/legumes can help decrease oxalate content, as well as levels of other antinutrients like phytate, protease inhibitors, lectins and tannins. For help with soaking and sprouting foods, refer to this sprout guide.
7. Talk to Your Doctor About Supplementing
Some people choose to take calcium citrate supplements, NAG (N-Acetyl-Glucos-amine), CMO (cetyl myristoleate) or a combination of these supplements to deal with oxalic acid-related side effects or pain. To help manage your symptoms, you can ask your doctor whether these might be helpful for you.
Also avoid taking more than 500 milligrams of vitamin C daily, since this will increase the amount of oxalate in your urine.
- Oxalic acid is a natural chemical found in many plants, including some vegetables, fruits, nuts, seeds, legumes and grains. It’s also isolated and used in cleaning/sterilizing because it’s a strong acid with corrosive effects.
- When found in food, oxalic acid is in the form of oxalates.
- Why is oxalate bad for you, and what are the side effects of oxalic acid? High oxalate symptoms/complications can include kidney stones, bladder problems, gastrointestinal issues and worsened fibromyalgia problems.
- A low-oxalate diet (similar to a kidney stone diet) involves avoiding high-oxalic acid foods, such as dark greens, rhubarb, leeks, okra, potatoes, peanuts, tea and chocolate. This type of diet should provides only 40 to 50 milligrams of oxalates per day or less.
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