In this lesson we will learn about oxalate.
We will learn why it is important in plants and the problems it can cause in humans. We will also learn about the structure of oxalate and how this structure affects calcium.
Popeye taught us all that eating our spinach will make us strong. Yes, spinach is very healthy and it’s high in many nutrients, including iron and calcium. Yet, since it’s also high in oxalate, our body can’t even use all of these nutrients.
Oxalate will bind iron and calcium, making it difficult for the body to absorb them.Oxalate is found in many plants and animal tissues. When it is bound to calcium, it has been found to cause kidney stones, which are crystals that can cause problems in the urinary tract. Yet this combination of calcium and oxalate could act as a protectant for plants, which we theorize is why it’s formed in the first place.
Foods with Oxalate
Some of the foods that are high in oxalate are: spinach, Swiss chard, rhubarb, beets, and nuts.
Of these, spinach and Swiss chard are of the most interest because all of the calcium and iron in them is not able to be absorbed once it’s bound to the oxalate. Some of the calcium and iron are not bound to oxalate and so can still be absorbed. Yet, foods high in oxalate aren’t as good of a source of calcium and iron as other foods may be. Oxalate can be partially destroyed by heat (cooking). Once it is destroyed, the body can then absorb the calcium and iron. Heat will also destroy other vitamins in the vegetables, such as vitamin C and A.
So, these foods can either be eaten raw and be a good source of vitamins such as C and A but not be a good source of calcium and iron, or they can be eaten cooked and be a good source of calcium and iron but not of the heat sensitive vitamins. We can also eat other vegetables such as kale, which is high in calcium and iron but does not contain oxalate.When the oxalate binds to calcium, it forms a crystal. These crystals can grow in the kidneys as they combine with each other. The more they grow, the larger the kidney stone formed. So, for those who are prone to kidney stones, it could help to avoid foods high in oxalate.
So what is oxalate, chemically? It’s simply carbon and oxygen, containing two carbon atoms and four oxygen atoms. It is a dianion, which means that it has a negative charge of two. This is why calcium associates so strongly with oxalate; it has a positive charge of two. Just like two magnets of opposite charges are attracted to each other, calcium and oxalate are attracted to each other. Calcium has the positive charge while oxalate has the negative charge; when these two combine it’s like a strong magnet holding them together. Oxalate also prevents other nutrients with a positive two charge from being absorbed, such as iron.
The oxalate formula is:
Oxalate is made of 2 carbon atoms and 4 oxygen atoms, with an overall negative two charge. This negative two charge is what can bind to minerals with a positive two charge, such as calcium.
These carbon atoms and oxygen atoms attach together to form the following structure:
The carbon atoms will form double bonds with any two of the oxygen atoms. This bond will often change from one oxygen atom to another; hence, the double bond is represented as a dotted line. The other two oxygen atoms that have no double bond have a negative charge. Since there are two oxygen atoms with a negative charge, the molecule has an overall charge of negative two.
As the oxalate can change where the double bond is, which is called resonance, the molecule is very stable. The ability for a molecule to have high resonance means that a high stress, such as a negative charge, can be shared by more molecules giving it more stability.
Oxalate is common in nature. It may be protective to the plants in which it is found. Yet in humans, it can cause urinary problems in the form of kidney stones.
Foods that are high in oxalate can prevent the calcium from being absorbed. This is because oxalate has a negative two charge and calcium has a positive two charge, which makes these two molecules attracted to each other.