<<Disclaimer: Verify this information before applying it to your situation.>>
A list of claims regarding oxalates. Myth or reality?
Claim: Oxalate prevents absorption of calcium.
The following info was taken from
http://nutrition.about.com/
Question: Is it true that that the oxalates in tea/milk or
chocolate/milk interfere with the absorption of calcium
from milk?
Answer: Yes, the oxalates in tea will interfere with the
calcium absorption from the milk. The oxalate in the tea
binds to calcium and is removed through the digestive
tract and not absorbed. Chocolate also contains oxalic
acid which will bind up some calcium. A cup of tea may
only have a small amount of milk added, so the tea may
bind up a fair amount of the calcium, but a glass of
chocolate milk would contain a lot more calcium than
oxalate and would still be a good source of calcium.
Sources:
Charrier MJS, Savage GP, Vanhanen, L. "Oxalate content and
calcium binding capacity of tea and herbal teas." Asia
Pacific Journal of Clinical Nutrition 11 (4), 298-301.
Brinkley L, McGuire J, Gregory J, Pak CY. "Bioavailability
of oxalate in foods." Urology. 1981 Jun;17(6):534-8.
---
Claim: Oxalate is a poison.
The following information taken from Professor Nancy
Lowry, Hampshire College, Amherst MA
(http://helios.hampshire.edu/~nlNS/mompdfs/oxalicacid.pdf)
As poisons go, oxalic acid is not lethal in teeny
quantities like those from poison darts frogs. The LD50
orally in rats is reported as 375 mg/kg; the Merck Index
reports the LD for dogs as 1 g/kg.
We can only make guesses about the poisonous doses for
people. Using the LD50 figure for rats, a 130 pound (58.9
kg) woman would need to consume about 22 grams of oxalic
acid to be in serious danger of death.
Rhubarb leaves contain 0.5-1.0% oxalic acid, so that you
would need to eat quite a large serving of the sour leaves
(perhaps 10 pounds) to get a lethal dose. However, a
fraction of that could nevertheless cause severe symptoms
of oxalic acid poisoning.
One neat quote I came across: “A few leaves won't hurt a
horse, a wheelbarrow full can kill pigs.”
One often repeated story features the English government
in World War I. It sent out an advisory encouraging its
citizens to eat rhubarb leaves to alleviate food shortages
and help the war effort. After sicknesses and deaths were
reported, the recommendation was rescinded.
Calcium binds very strongly to the oxalate anion, forming
calcium oxalate, which is extremely insoluble in water.
Because of the strength of the calcium/oxalate pair foods
rich in both calcium and oxalate are pretty useless as a
source of calcium. In addition, cooking does not wash out
oxalate from sources that are high in oxalate and calcium,
although it does help in foods that are high in potassium
oxalate like skunk cabbage. [That goes for iron also, so
spinach is not a good source of iron (Popeye to the
contrary) because the iron is tightly bound to oxalate and
therefore not available for the body’s use.]
Table I: Oxalic acid content in selected vegetables.
These are ballpark numbers, actual content depends on many
variables.
See note ate the end of the article.
Vegetable - Oxalic acid (g/100 g)
Asparagus - 0.13
Broccoli - 0.19
Lettuce - 0.33
Brussels sprouts - 0.36
Collards - 0.45
Beet leaves - 0.61
Spinach - 0.97 (0.32-1.26)
Purslane - 1.31
Parsley - 1.70
Selected References:
Amounts of oxalic acid in various foods:
USDA: Oxalic Acid Content of Selected Vegetables:
http://www.nal.usda.gov/fnic/foodcomp/Data/Other/oxalic.html
Food Science, Lincoln University, NZ: Oxalate Containing
Foods
http://www.foodscience.ac.nz/research_topics/oxalate/Oxalate_containing_food.html
Mallinckrodt Baker, Inc. MSDS. Fatal dose figure for
oxalic acid:
http://www.jtbaker.com/msds/englishhtml/o6044.htm
Shooting crystals:
Dr. T. Ombrello, Union County College: Plant of the Week:
Dumbcane
http://faculty.ucc.edu/biology-ombrello/POW/dumbcane.htm
Dr. T. Ombrello, Union County College
http://www.cook.rutgers.edu/~floriculture/publications/dumbc.htm
Mary C. Smith, DVM: Oxalate Poisoning: Horse and pig quote
http://www.maltawildplants.com/OXIL/Docs/Oxalate%20Poisoning.htm
LD50 figures can seem to be wildly different as well as
notoriously difficult to extend to people. The calculation
of the lethal amount of rhubarb leaves above was based on
an LD50 orally in rats of 375 mg/kg and calculates to a
fatal dose of oxalic acid of about 22 grams of oxalic
acid.. However, another MSDS estimates that the fatal dose
would be about 5 to 15 grams. In addition, the amount of
oxalic acid in a blade of rhubarb is not a fixed number,
but depends on leaf size, soil, developmental stage at the
time of picking, the particular species of rhubarb, and
more. Clearly, this is not an exact but complicated
science!
---
Claim: Oxalate causes vulvodynia.
In early 2006, there were two articles on the PubMed
database that involved research into oxalates and
vulvodynia. The first article from 1991 (PMID:1816400:)
was a case report of a woman that had suffered from
vulvodynia for 4 years, and the condition had become
debilitating. A series of tests showed that the
alkalinity and oxalate level of her urine often rose to
abnormal levels, and her discomfort was linked to these
surges in oxalates. The woman was put on a program to
control oxalates that included a calcium citrate
supplement. The woman improved significantly by a 3 month
follow up, and was symptom free after a year on calcium
citrate. When the woman stopped taking calcium citrate,
her symptoms would return; when she restarted the
supplement, her vulvodynia went into remission. So in one
case, a strong relationship between oxalates and vulvular
pain was demonstrated.
A second study was conducted in 1997 that included 130
women with vulvular pain syndrome (PMID:9322615). Lab
tests showed that just under half of the women (59
patients) had elevated oxalate levels. These 59 were put
on a program that included a low oxalate diet and calcium
citrate. The results of this study were less dramatic than
in the first case study: 24% (14 patients) demonstrated an
'objective improvement' and 10% (6 patients) improved to
the point of being able to have normal sexual intercourse.
The researchers concluded that oxalates might aggravate
vulvodynia, but was not the cause for most women in the
study.
From the limited research (and from anecdotal information
on the web), it can be said that a program to reduce
oxalates in the diet along with a supplement of calcium
citrate might provide a measure of relief to some women
with vulvodynia.
---
An interesting perspective:
Having excess oxalates in your body (whatever the reason)
is somewhat analogous to having diabetes. Eating sugar
doesn't cause diabetes, and eating foods high in oxalate
doesn’t cause the symptoms and conditions associated with
high oxalate levels. However, cutting sugar/carbohydrates
out of your diet is part of the treatment for diabetes.
Likewise, the low oxalate diet is part of an overall
dietary regimen to prevent things like kidney stones,
interstitial cystitis, fibromyalgia, vulvodynia, or
connective tissue disorders in general.
Visit the Celiac Web Page at Http://www.enabling.org/ia/celiac/index.html
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