When most of us hear the words oxalic acid we think of dark, green leafy vegetables. The incredible health benefits of these veggies is well documented. Nutrient dense, they have been known to assist in the healing of life threatening illnesses and disease. However, there is one area where they get a bad rap; and that is the oxalic acid content. The problem with oxalic acid is the oxalate crystals that form when oxalic acid combines with calcium forming a salt called oxalate.
Oxalate can form in the body from other sources besides diet:
- fungus such as Aspergillus and Penicillium and possibly Candida
- and from human metabolism
- ascorbic acid (vit C)
There is a lot of controversy surrounding oxalic acid. Despite the plethora of articles on the web, there is little hard data. After extensive research, I put together the most current information.
What is oxalic acid?
- Oxalic acid is a naturally occurring chemical in plants and animals
- oxalic acid combines with calcium and forms a salt called oxalate
- oxalate create two health concerns; calcium deficiency and the formation of kidney stones.
Facts about kidney stones:
The formation of kidney stones containing oxalate is an area of controversy in clinical nutrition. Does the dietary restriction of oxalate prevent kidney stones? Not according to these facts:
- kidney stones are the result of an accumulation of dissolved minerals on the inner lining of the kidneys.
- The leading cause of kidney stones is a lack of water.
- When there is not enough water to dilute the uric acid, the pH level within the kidneys drops and becomes more acidic.
- An excessively acidic environment in the kidneys is conducive to the formation of kidney stones.
- Not all stones are related to oxalate
- It is not clear from the research, that restriction of dietary oxalate helps prevent formation of calcium oxalate stones in individuals who have previously formed such stones.
- Since intake of dietary oxalate accounts for only 10-15% of the oxalate that is found in the urine of individuals who form calcium oxalate stones, many researchers believe that dietary restriction cannot significantly reduce risk of stone formation.
- recent research studies have shown that intake of protein, calcium, and water influence calcium oxalate stone formation as much as, or more than intake of oxalate.
- some foods that have traditionally been assumed to increase stone formation because of their oxalate content (like black tea) actually appear in more recent research to have a preventive effect.
- the normal human body can dispose of oxalic acid at even relatively high dietary quantities without trouble
- though oxalic acid is very poorly absorbed, it is readily enough excreted.
Facts about calcium:
- oxalic acid may reduce one’s effective intake of calcium. But if you are getting decent nourishment, the size of the effect is not meaningful.
- While research studies confirm the ability of phytic acid and oxalic acid in foods to lower availability of calcium, the decrease in available calcium is relatively small.
- For normal, healthy persons, calcium deficiency risk is nearly trivial provided that great amounts of oxalic acid are not consumed on a continuing, long-term basis.
- The National Institute of Health states “For people who eat a variety of foods, these interactions probably have little or no nutritional consequence and, furthermore, are accounted for in the overall calcium DRIs [Dietary Reference Intakes], which take absorption into account.”
Oxalates and calcium supplements:
- High oxalate in the urine and plasma was first found in people who were susceptible to kidney stones.
- Because many kidney stones contain calcium, some people think they should avoid calcium supplements.
The opposite is true of calcium supplementation:
- When calcium is taken with foods high in oxalates, the oxalic acid combines with calcium and is eliminated in the stool.
- Insoluble calcium oxalate crystals cannot be absorbed into the body.
- When calcium is low in the diet, oxalic acid is soluble and is readily absorbed from the intestine into the bloodstream.
- If oxalic acid is very high in the blood being filtered by the kidney, it may combine with calcium to form crystals that may block urine flow and cause severe pain.
Is cooking a solution? Not really.
The effect of cooking on oxalates
- Cooking has a relatively small impact on the oxalate content of foods
- Repeated food chemistry studies have shown no statistically significant lowering of oxalate content following the blanching or boiling of green leafy vegetables.
- A lowering of oxalate content by about 5-15% is the most you should expect when cooking a high-oxalate food.
- It does not make sense to overcook oxalate-containing foods in order to reduce their oxalate content as many vitamins and minerals are lost from overcooking more quickly than are oxalates, the overcooking of foods (particularly vegetables) will simply result in a far less nutritious diet that is minimally lower in oxalates.
Other factors that influence the effects of oxalic acid:
Genetics – The extent to which foods high in oxalic acid are a potential health problem varies from person to person.
- According to the National Institutes of Diabetes and Dietary and Kidney Diseases (NIDDK), genetics and family history contribute strongly to kidney stone formation.
- Calcium oxalate kidney stones form in individuals who have high levels of calcium, oxalate and acid in their urine.
- The exact reasons for above normal levels of calcium and oxalate are largely unknown but can involve genetic factors that regulate the absorption of calcium and oxalate and promote kidney stone formation.
- Individuals with especial vulnerability to oxalates–notably those with kidney disorders, gout, rheumatoid arthritis, or certain forms of chronic vulvar pain (vulvodynia)–need to be careful about their intake of oxalic acid.
- Normally healthy people probably do not.
Acid in the Urine
- Calcium oxalate and calcium phosphate precipitate from the urine more readily to form a stone when urine becomes too acidic.
- A diet rich in protein and meats can increase urine acidity and help stones to form.
- Insulin resistance also increases urine acidity and the risk for stone formation, putting diabetics and obese individuals at risk for calcium stones.
- Calcium, oxalate, and acids also concentrate in the urine of individuals with inadequate fluid intake levels.
- For this reason, it is recommended that those at risk for calcium kidney stones drink at least 12 glasses of water per day. This will help to flush excess calcium and oxalate from the kidneys and also help to decrease urine acidity.
Who really needs to restrict their dietary intake of oxalic acid:
- Folks who have another condition, genetic in origin, that impairs their bodies’ ability to process oxalic acid
- oxalic acid is not the cause of their problems, but it is the raw material for it
- these people do indeed need to regulate their intake, just as diabetics need to monitor their sugar intake despite sugar normally being a harmless substance.
- Those with a need for caution include sufferers from kidney disorders and kidney stones, gout, rheumatoid arthritis, and certain forms of chronic vulvar pain (vulvodynia).
Conditions that require strict oxalate restriction
- There are a few, relatively rare health conditions that require strict oxalate restriction.
- These conditions include absorptive hypercalciuria type II, enteric hyperoxaluria, and primary hyperoxaluria.
- Dietary oxalates are usually restricted to 50 milligrams per day under these circumstances
Other diseases that may be caused from the effects of excess oxalate:
- kidney disease
- vulvar pain
- may increase inflammation
- Iron oxalate crystals may also cause significant oxidative damage and diminish iron stores
- Oxalates may chelate many toxic metals such as mercury and lead, trapping these heavy metals in the tissues.
- Sheer toxicity–actual poisoning–from ingested oxalic acid is wildly unlikely.
- The only foodstuff that contains oxalic acid at concentrations high enough to be an actual toxicity risk is the leaves (11 lbs. in one sitting) of the rhubarb plant.
- For just about every other foodstuff, the risk–if any–is not immediate toxicity but a contribution to the development of oxalate crystals.
- However, our bodies always contain oxalates, and our cells routinely convert other substances into oxalates.
- For the vast majority of individuals, oxalate-containing foods should not be a health concern.
- Under most circumstances, high oxalate foods like spinach can be eaten raw or cooked and incorporated into a weekly or daily meal plan
- the decision about raw versus cooked or baby versus mature leaf spinach or other oxalate-containing vegetables, should be a matter of personal taste and preference for most individuals.
If kidney stones are a concern
- make sure to work with a natural health practitioner that you trust, preferably one who is familiar with and supportive of the raw food diet.
- Secondly, eliminate salt, even Celtic sea salt, from your diet as much as possible! Salt is a constant irritation to the renal system.
- make sure you are eating a wide variety of alkaline foods
- Be sure to rotate your greens in juices, smoothies and other recipes to make sure that you are not taking in excessive amounts of any one substance, but rather moderate amounts of a wide variety of nutrients.
- Alternate between raw foods that are high in oxalic acid, and those that aren’t.
The Raw community has this to say about oxalic acid:
- There is a big difference between cooked and raw forms of oxalic acid.
- When cooked, it is not actually a nutrient in the body, so the body naturally processes it into the most convenient form to be excreted, usually through the urine.
- Since calcium is an alkaline mineral, the body will leech it from the bones to equalize the pH balance in the blood.
- The remaining calcium is eliminated through the urine in the form of calcium oxalate.
- f levels are high enough, the calcium will crystallize and form small clumps that become stones.
- A raw food diet can be an invaluable aid to alkalize the blood.
Dr. Gabriel Cousens says
- Organic oxalic acid, defined as that which occurs in nature in its raw form, can actually be beneficial to the system.
- Once foods containing oxalic acid are cooked, according to, Dr. Norman Walker, the oxalic acid becomes a dead and irritating substance to the system.
- He feels that in its cooked form it binds irreversibly with the calcium and prevents calcium absorption.
- An excess of cooked oxalic acid may also form oxalic acid crystals in the kidney.
Dr. Norman Walker claims
- in the live organic form, oxalic acid does not present any problem.
- Oxalic acid stones and calcium blockage do not occur because the organic oxalic acid can be metabolized appropriately.
- oxalic acid in its raw form is one of the important minerals needed to maintain tone and peristalsis of the bowel.”
Foods that contain oxalates
The following are some examples of the most common sources of oxalates, arranged by food group. It is important to note that the leaves of a plant almost always contain higher oxalate levels than the roots, stems, and stalks.
- concord (purple) grapes
Most oxalate dense vegetables:
- Swiss chard
- beet greens
Moderately dense veggies:
- green beans
- summer squash
Nuts and seeds
- other soy products
- wheat bran
- wheat germ
- black tea