Oxalic Acid: Not as bad as we think?

[RedfootsRule]

I figured this is a debate that needed to be had....It could potentially be very beneficial to all of our tortoises if what I'm hoping is proven...

Oxalic acid is one thing I have strived to understand for some time now. I recently saw a claim that we need to limit dandelion greens because of the oxalic acid content...
Earlier, I was working with my brother, who is a biochemist. I made a comment about my star fruit tree, and all of the fruit it had, but I was worried about feeding it to my tortoises because of the high amount of oxalic acid...This prompted a lengthy discussion about it.

No evidence has yet been presented to prove that oxalic acid actually has any harmful effect to our shelled companions (obviously it can in some ways, we'll get to that)...Most just figure to be on the safe side because of what it does to humans. But comparing mammals to reptiles is rather irrelevant. The digestive and metabolism systems are so much different.


Here's an illustration of oxalic acid. From the understanding I got from my brother, judging by the nature of this compound, two oxalates will have to form together to "wrap around" and bind a calcium ion. This means that unless there are twice as much oxalates then calcium in the food you feed, there is no harm. If you look at the amounts of calcium to oxalic acid in most foods you feed, there is no danger. Especially if you pair up a food with super-high calcium, like collard greens, in a meal containing large amounts of oxalic acid.

But heres the problem: Calcium oxalates, if stored in the liver, which they tend to be by reptiles, are a main component of kidney stones. This obviously presents a threat to our shelled companions. But how often is it stored, and how often is it passed? And how often is it actually used to make stones? Are there certain ways in feeding to get around it being stored by the liver? I honestly don't understand how it can be harmful, because in all plants, calcium and oxalic acid come hand in hand....There was a reason for that that my brother explained...Something about that for there to be calcium, there had to be oxalic acid to keep it there? I'm not completely sure. But it is true that the two are always together, so how can it be harmful?
From the research I've done about oxalic acid, it appears that hydration is a key. This is already known in reptiles; hydration seems to be key to everything. But if there is plenty of hydration, it apparently significanly decreases the risk of stones.
Magnesium is a mineral that leafy greens is rich in....Which we feed a lot of. On studys done on several different animals, it has become apparent that with the correct amounts of magnesium (which is certain in the diet of most chelonians), the risk of stones are also lowered.
I don't like using the comparison of humans to reptiles, but most all ways of limiting kidney stone formation that is caused by calcium oxalate is to increase leafy greens and fruits in the diet, and decrease meats. Greens are abundant in tortoise' diets, and meat is very low.

From the research I've seen, it seems that dehydration is a key element in kidney stones. That, coupled with too little Vitamin A (which is high in most foods we feed), Vitamin D, and too much calcium is going to result in kidney stones. It seems the oxalic acid is just a small contributor to it; certainly not the main culprit.

Wild tortoises are known to eat plants considered dangerously high in oxalates. Bladder stones are also found in wild tortoises....They are not a death sentence. I'm not completely sure of the harm of them, but I believe it to only be if they are broken inside that they can cause harm?


If oxalic acid is not harmful as we think it is, then it would eliminate all worry of oxalates, and possibly allow us to utilize a larger range of food sources...But nothing is perfect until it is peer-reviewed . So, if anyone has knowledge in this field, please give me your opinion, and correct me where I'm wrong. I really want this to be solved, for my own learning and that of others.

 

[acrantophis]

I will give you a bump. I limit my dandelion and would love to give more.

 

[N2TORTS]

http://www.tortoiseforum.org/thread-37761.html

 

[mattgrizzlybear]

I love how much people care for their tortoises! Everybody takes every little precaution to prevent an accident. Thank you and I will maybe cut down the dandy lions unless I feed them with calcium greens. Thank you!

 

[RedfootsRule]

Matt, I'm pretty sure dandelion greens in itself have enough calcium to counter-act the effect of oxalates

 

[luckyduck517]

I'll jump in here just with a few quick comments. Admittedly, my knowledge in this area isn't where I would like it to be, which I think is in part due to the fact that there is very little "proven" research out there. There are a few peer reviewed articles that I've seen which are reasonably current in which oxalate crystals were found in the kidneys of wild tortoises. However, of the many necropsies done, only a few were found to have renal damage as well as oxalate crystals: others had crystals but no evidence of renal damage. One study I read discussed desert tortoises, which means that it is likely the animals were exposed to drought type conditions, and we know that dehydration is a factor in crystal accumulation. In my mind, the conclusion is this: in a well cared for pet tortoise with good hydration, oxalate crystals themselves are not very likely to cause a problem.

However, another consideration is that oxalate binds calcium, and I think this is were there is more concern, especially in young tortoises that are sensitive to metabolic bone disease and ones that cannot be raised outside. So to me, like was mentioned above, foods high in oxalate aren't poisonous, as long as they are given in a varied diet and there is enough calcium and D3 provided to the tortoise, and tortoises are well hydrated. That's how I think about it, anyway: feel free to correct any errors I've made!

 

[RedfootsRule]

I definitely agree; hydration has a lot to do with the effect of it. Could you possibly send me some of the articles your talking about? If you have them, or know where to find them, that is.

This was part of my point. The amount of calcium in the foods we feed is WAY over the top. So basically, pair a food that has high oxalates up with a high calcium food (collard greens, papaya, etc.) and there should be no damage as far as MBD goes. My main worry is oxalate crystals; but I don't think its as much of a worry as we think. Most worry about it because of stones, but it doesn't seem that its as much of a contributor as its suspected to be.

 

[marcy4hope]

So basically, pair a food that has high oxalates up with a high calcium food (collard greens, papaya, etc.) and there should be no damage as far as MBD goes.

i have a 17 month sulcata that was diagnosed with bladder stones in november. i think hydration comes into play. i had him hydrated well, but don't know how he was raised the first 5 months of his life before i got him. since he was diagnosed, i cut back on protein and anything i thought was high in oxalates.

i was told that collard greens should be avoided because they were high in oxalates, but i noticed you mention them being high in calcium and a good balance for something else high in oxalates? my sully loves them so i hate to cut back on them too much, but obviously i will if needed. what do you think, since you are discussing this oxalate issue?

 

[RedfootsRule]

So basically, pair a food that has high oxalates up with a high calcium food (collard greens, papaya, etc.) and there should be no damage as far as MBD goes.

i have a 17 month sulcata that was diagnosed with bladder stones in november. i think hydration comes into play. i had him hydrated well, but don't know how he was raised the first 5 months of his life before i got him. since he was diagnosed, i cut back on protein and anything i thought was high in oxalates.

i was told that collard greens should be avoided because they were high in oxalates, but i noticed you mention them being high in calcium and a good balance for something else high in oxalates? my sully loves them so i hate to cut back on them too much, but obviously i will if needed. what do you think, since you are discussing this oxalate issue?

The oxalates in collard greens are really not that high. The calcium/oxalate ratio is about 145 - 0.07 (grams). I use it as a staple in some of my tortoises' diets, for years now, and have never seen any negative effect. I, personally, would not worry about collards at all.

Hydration definitely seems to play a critical role in stone development. I really don't think calcium oxalate crystals are as much of a contributor as people make them out to be.

 

[marcy4hope]

The oxalates in collard greens are really not that high. The calcium/oxalate ratio is about 145 - 0.07 (grams). I use it as a staple in some of my tortoises' diets, for years now, and have never seen any negative effect. I, personally, would not worry about collards at all.

Hydration definitely seems to play a critical role in stone development. I really don't think calcium oxalate crystals are as much of a contributor as people make them out to be.

thanks. i really appreciate your opinion. this has become a very interesting topic for me as to relation to bladder stones since i've been dealing with it. i'll keep watching this thread.

 

[paludarium]

I'll jump in here just with a few quick comments. Admittedly, my knowledge in this area isn't where I would like it to be, which I think is in part due to the fact that there is very little "proven" research out there. There are a few peer reviewed articles that I've seen which are reasonably current in which oxalate crystals were found in the kidneys of wild tortoises. However, of the many necropsies done, only a few were found to have renal damage as well as oxalate crystals: others had crystals but no evidence of renal damage. One study I read discussed desert tortoises, which means that it is likely the animals were exposed to drought type conditions, and we know that dehydration is a factor in crystal accumulation. In my mind, the conclusion is this: in a well cared for pet tortoise with good hydration, oxalate crystals themselves are not very likely to cause a problem.

However, another consideration is that oxalate binds calcium, and I think this is were there is more concern, especially in young tortoises that are sensitive to metabolic bone disease and ones that cannot be raised outside. So to me, like was mentioned above, foods high in oxalate aren't poisonous, as long as they are given in a varied diet and there is enough calcium and D3 provided to the tortoise, and tortoises are well hydrated. That's how I think about it, anyway: feel free to correct any errors I've made!

Wow, I totally agree with you. I also did some readings in articles and veterinary textbooks. Calcium oxalates in the foods seem not to cause any problem, but dehydration does.

Some of the must read researches:
http://www.ncbi.nlm.nih.gov/pubmed/19901374
http://www.ncbi.nlm.nih.gov/pubmed/18714683
http://www.ncbi.nlm.nih.gov/pubmed/19038651

Regards,
Erich

 

[CtTortoiseMom]

The oxalates in collard greens are really not that high. The calcium/oxalate ratio is about 145 - 0.07 (grams). I use it as a staple in some of my tortoises' diets, for years now, and have never seen any negative effect. I, personally, would not worry about collards at all.

Hydration definitely seems to play a critical role in stone development. I really don't think calcium oxalate crystals are as much of a contributor as people make them out to be.

thanks. i really appreciate your opinion. this has become a very interesting topic for me as to relation to bladder stones since i've been dealing with it. i'll keep watching this thread.

Did you read the link JD (N2Tort's)posted? It is a thread from a year ago about this exact subject. The info in their is excellent. A really informative read.

 

[Spn785]

Thanks Everyone for the great read! This is really good information.

 

[marcy4hope]

Did you read the link JD (N2Tort's)posted? It is a thread from a year ago about this exact subject. The info in their is excellent. A really informative read.

yep - i read that. it was a good read. i bookmarked it so i could find it easier later too. the 3 articles someone else just posted were very interesting too.

 

[paludarium]

Hi,

here is another excellent article to read:
Report on the Analysis of the Wild Diet of Testudo werneri

A quote from the summary:
" The results of the nutritional analysis revealed a high calcium to phosphorous ratio and a surprisingly high oxalic acid content."

Regards,
Erich

 

[GeoTerraTestudo]

This is a great thread, as is JD's thread on this topic from last year. I also appreciate the link to the scientific article above.

I agree that oxalate is overrated as a threat to tortoise health. A lot of plants contain it, and tortoises have a high tolerance for it. As Lucky Duck said, a varied diet is important so that tortoises can "spread out" both the benefits and risks of the foods they eat. Foods may differ in their nutrient and anti-nutrient content, so by eating different things, the animals get the vitamins and minerals they need, and they minimize the intake of oxalate, goitrogens, alkaloids, and other toxic compounds.

I think dandelions are safe for tortoises, as are collards, and many other greens. Just keep the diet varied, and I think the tortoises will thrive.

From the understanding I got from my brother, judging by the nature of this compound, two oxalates will have to form together to "wrap around" and bind a calcium ion. This means that unless there are twice as much oxalates then calcium in the food you feed, there is no harm.

I would amend that statement a bit. If two molecules of oxalate are required to bind one atom of calcium, then that means for every two mols of oxalate, one mol of calcium will be unavailable. The atomic weight of oxalic acid is about 90 g/mol. The atomic weight of calcium is around half that - about 40 g/mol. Thus, a given weight of oxalic acid would bind about 1/4 its weight of calcium.

So, for an easy example, if a plant contains 4 g of oxalate and 10 g of calcium, the oxalate is binding only about 1 g of the calcium. That leaves 9 g available to the animal for absorption. Thus, as was mentioned above, the bigger threat is that oxalate (or calcium) could crystallize in the kidneys or liver, potentially killing the tortoise. The best way to minimize this risk is to make sure the tortoise stays well hydrated, gets a varied diet, and does not OD on calcium.

 

[paludarium]

From the understanding I got from my brother, judging by the nature of this compound, two oxalates will have to form together to "wrap around" and bind a calcium ion. This means that unless there are twice as much oxalates then calcium in the food you feed, there is no harm.

I would amend that statement a bit. If two molecules of oxalate are required to bind one atom of calcium, then that means for every two mols of oxalate, one mol of calcium will be unavailable. The atomic weight of oxalic acid is about 90 g/mol. The atomic weight of calcium is around half that - about 40 g/mol. Thus, a given weight of oxalic acid would bind about 1/4 its weight of calcium.

So, for an easy example, if a plant contains 4 g of oxalate and 10 g of calcium, the oxalate is binding only about 1 g of the calcium. That leaves 9 g available to the animal for absorption. Thus, as was mentioned above, the bigger threat is that oxalate (or calcium) could crystallize in the kidneys or liver, potentially killing the tortoise. The best way to minimize this risk is to make sure the tortoise stays well hydrated, gets a varied diet, and does not OD on calcium.

Just don't understand, calcium oxalate or CaC2O4 means only one molecule of oxalic acid is bound to one atom of calcium.

Correct me if I am wrong. Maybe the oxalate contents of the plants are generally presented as total oxalate levels, however, it should be the soluble oxalate that binds to the calcium. The soluble oxalate not only binds with calcium, but also to other minerals.

A good example from this research: Bioavailability of soluble oxalate from spinach eaten with and without milk products. It shows that frozen commercially available spinach in New Zealand contains 736.6+/-20.4 mg/100g wet matter (WM) soluble oxalate and 220.1+/-96.5mg/100g WM insoluble oxalate. The frozen spinach contained 90mg total calcium/100g WM, 76.7%of this calcium was unavailable as it was bound to oxalate as insoluble oxalate.

Regards,
Erich

 

[GeoTerraTestudo]

Just don't understand, calcium oxalate or CaC2O4 means only one molecule of oxalic acid is bound to one atom of calcium.

Based on the OP, I thought it took two oxalate molecules to bind one calcium atom. Since oxalate weighs twice as much as calcium, that would mean that a given weight of calcium would be bound by 4x that weight in oxalate. That's my understanding, anyway. Please correct me if I'm wrong.

 

[RedfootsRule]

This is a great thread, as is JD's thread on this topic from last year. I also appreciate the link to the scientific article above.

I agree that oxalate is overrated as a threat to tortoise health. A lot of plants contain it, and tortoises have a high tolerance for it. As Lucky Duck said, a varied diet is important so that tortoises can "spread out" both the benefits and risks of the foods they eat. Foods may differ in their nutrient and anti-nutrient content, so by eating different things, the animals get the vitamins and minerals they need, and they minimize the intake of oxalate, goitrogens, alkaloids, and other toxic compounds.

I think dandelions are safe for tortoises, as are collards, and many other greens. Just keep the diet varied, and I think the tortoises will thrive.

From the understanding I got from my brother, judging by the nature of this compound, two oxalates will have to form together to "wrap around" and bind a calcium ion. This means that unless there are twice as much oxalates then calcium in the food you feed, there is no harm.

I would amend that statement a bit. If two molecules of oxalate are required to bind one atom of calcium, then that means for every two mols of oxalate, one mol of calcium will be unavailable. The atomic weight of oxalic acid is about 90 g/mol. The atomic weight of calcium is around half that - about 40 g/mol. Thus, a given weight of oxalic acid would bind about 1/4 its weight of calcium.

So, for an easy example, if a plant contains 4 g of oxalate and 10 g of calcium, the oxalate is binding only about 1 g of the calcium. That leaves 9 g available to the animal for absorption. Thus, as was mentioned above, the bigger threat is that oxalate (or calcium) could crystallize in the kidneys or liver, potentially killing the tortoise. The best way to minimize this risk is to make sure the tortoise stays well hydrated, gets a varied diet, and does not OD on calcium.

Thats actually not something I considered, but your very right....So then, binding calcium is even less of a worry.

So really, unless a tortoise has MBD, in my understanding, the only worry is crystallization of the oxalates, forming kidney stones. What I would really like to know is the actual likelihood of that. It seems like the possibility is mainly based off of how well the tortoise is hydrated. Also, make sure the tortoises are not deficient in Vitamin A or D, but most of the vegetables we feed are very high in both of these.

Very smart Geo, thanks for the input .

 

[Baoh]

The lack of understanding of chemistry in this thread is expected, but still somehow still sorely disappointing. The bonding has nothing to do with the mass. It has to do with the charge. There is a liberation of two hydrogens from the hydroxyls (one from each) that serves to bind the free calcium ion. One oxalic acid molecule binds to one free Ca2+ ion (dication) to form one molecule of calcium oxalate after rotation along the alkane bond between carbon atoms so that it can reach a most stable conformation.

Also, hydration is irrelevant to calcium oxalate. Ca2+ is soluble in aqueous solution. Oxalic acid is soluble in aqueous solution. Calcium oxalate forms when they encounter each other and then precipitation occurs due to aqueous insolubility. That is even the basis of USP methodology to test for the identifcation of calcium. It is extremely simplistic chemistry and I worked in one of the major commercial laboratories as an analytical chemist working most of the time with calcium compounds as my first job after graduating from my undergraduate program, so I performed this for over a year and a half and it was probably among the most basic assays I had to perform.