Oxalate

Green leafy vegetables and other plant foods are very popular with health-conscious people. However, many of these foods contain a so-called "anti-nutrient" known as oxalate (oxalic acid). This article will look at the benefits and risks of consuming this compound.

What is oxalate?

Oxalic acid is an organic compound found in many plants. This includes green leafy vegetables, other vegetables, fruit, cocoa, nuts and seeds (1). In plants, oxalic acid is usually found bound to minerals in the form of oxalate. However, the terms oxalic acid and oxalate are used interchangeably in the field of nutritional science. The human body can either produce oxalate itself or absorb it through food. Vitamin C can also be converted into oxalate when it is metabolized (2). Once consumed, oxalate can combine with minerals to generate chemical compounds that include calcium oxalate and iron oxalate. This occurs mainly in the intestines, but can also take place in the kidneys and other areas of the urinary tract. In most people, these compounds are excreted in the stool or urine. However, in oxalate-sensitive people, oxalate-rich diets have been associated with an increased risk of kidney stones and other health problems. Summary: Oxalate is an organic acid that is found in plants but can also be produced by the body. It combines with minerals and has been linked to kidney stones and other health problems.

Oxalate can reduce mineral absorption

One of the primary health concerns regarding oxalate is that it can bind minerals in the digestive tract, preventing absorption of these minerals by the body. Spinach, for example, is rich in calcium and oxalate, which means that a lot of the calcium it contains is not absorbed by the body (3). Eating fiber in combination with oxalate can also prevent nutrient absorption (4). Nevertheless, it is important to remember that only some of the minerals found in our food are bound by oxalate. And although calcium absorption of calcium contained in spinach is reduced, calcium absorption of calcium contained in milk is not affected when milk and spinach are consumed together (3).

Summary: Oxalate can bind minerals in the digestive tract and prevent some of these minerals from being absorbed, especially when combined with dietary fiber.

Oxalate could contribute to the formation of kidney stones

Normally, calcium and small amounts of oxalate are present in the urinary tract at the same time, but they both remain dissolved in the urine and therefore do not cause problems. However, sometimes these two substances combine and form crystals. These crystals can lead to the formation of kidney stones in some people, especially if the amount of oxalate is high and the volume of urine is low (5).

Small stones often cause no problems, but large stones can cause serious pain, nausea and blood in the urine as they move through the urinary tract. Although there are different types of kidney stones, 80% of them are made up of calcium oxalate (5). For this reason, people who have had problems with kidney stones in the past are advised to minimize their consumption of oxalate-rich foods (5, 6). Today, however, a blanket oxalate restriction is no longer recommended for all people with kidney stones. This is due to the fact that most of the oxalate found in urine is produced by the body itself and not ingested through food (7). Most urologists now only prescribe a strict low oxalate diet (less than 50 mg oxalate per day) to patients with high urinary oxalate levels (6). For this reason, it is important to measure oxalate levels from time to time to determine how much oxalate restriction may be necessary.

Summary: Oxalate-rich foods may increase the risk of kidney stones in susceptible people and recommendations for patients should be based on urine levels.

Does oxalate cause other problems?

Some people claim that high oxalate intake may be linked to the development of autism. Others say that oxalates may be linked to vulvodynia, which is characterized by chronic, unexplained vaginal pain. However, based on the current state of research, scientists do not believe that any of these disorders could be caused by oxalates (8, 9, 10). However, when 59 women suffering from vulvodynia were treated with a low oxalate diet and calcium supplements, almost a quarter of these women experienced an improvement in symptoms (10). The authors of this study concluded that dietary oxalate may not cause the condition, but could exacerbate it. Numerous online anecdotes link oxalates to autism and vulvodynia, but few studies have looked at possible links. Further studies are therefore needed for a conclusive assessment.

Summary: Some people suggest that consumption of oxalate-rich foods may lead to autism and vulvodynia, but at this time this is not supported by scientific studies.

Most foods containing oxalates are very healthy

Some advocates of a low oxalate diet say that people would be better off avoiding foods rich in oxalates as they may have negative side effects. However, it's not quite that simple. Many of these foods are healthy foods that contain important antioxidants, fiber and nutrients. For this reason, it is not a good idea for most people to completely avoid eating oxalate-rich foods.

Summary: Many foods that contain oxalates are delicious and have many health benefits. Avoiding these foods is not necessary for most people and may even have negative effects.

The digestive tract determines oxalate absorption

Some of the oxalates you consume in your diet are broken down by bacteria in the digestive tract, which happens before these oxalates can bind minerals. One of these bacteria called Oxalobacter formigenes even uses oxalates as a source of energy. This significantly reduces the amount of oxalate your body absorbs (11). However, some people do not have large amounts of this bacterium in their digestive tract, as antibiotics can reduce the number of colonies of this bacterium (12). In addition, studies have found that people who suffer from inflammatory bowel disease are at increased risk of developing kidney stones (13, 14). This is partly due to their inability to regulate the amount of oxalate they absorb. Elevated oxalate levels have also been found in the urine of patients who have had gastric bypass surgery or other operations that alter the function of the digestive tract (15). This suggests that people who have taken antibiotics or suffer from digestive tract dysfunction may benefit more from a low oxalate diet.

Summary: Most healthy people can consume oxalate-rich foods without problems, but people with altered digestive tract function may benefit from reducing their oxalate intake.

Oxalate-rich foods

Oxalates are found in almost all plants, but some plants contain very high amounts, while others contain only very small amounts. Animal foods, on the other hand, only contain traces of oxalate.

Foods with a high oxalate content (100 to 900 mg per serving) include

Rhubarb
spinach
Beet
Swiss chard
endive
Cocoa powder
Kale
Sweet potatoes
Peanuts
Star fruit

Summary: The amount of oxalates varies from extremely high to very low. Foods are classified as high in oxalates if they contain 100 to 900 mg of oxalate per serving.

How to eat a low oxalate diet

People who should follow a low-oxalate diet due to kidney stones are often instructed to consume less than 50 mg of oxalate per day. Here are a few tips to follow when on a low oxalate diet:

Limit your oxalate intake to 50 mg per day: choose a variety of animal and plant foods that are high in nutrient density but low in oxalate. You can find lists of low oxalate foods on the internet.
Cook oxalate-rich vegetables: Cooking vegetables can reduce oxalate levels by 30 to 90%, depending on the food (17).
Drink plenty of water: Aim for at least 2 liters per day. If you suffer from kidney stones, you should drink enough to produce at least 2.5 liters of urine per day (6).
Get enough calcium: Calcium binds oxalate in the digestive tract and reduces the amount of oxalate your body absorbs. Try to get 800 to 1,200 mg of calcium per day (1, 16)

Foods that are high in calcium and low in oxalate include:

Cheese
plain yogurt
Canned fish with bones
Bok choy
broccoli

Summary: A diet with less than 50 mg of oxalate can be balanced and nutritious. Calcium can also help reduce the absorption of oxalate.

Should you avoid oxalate?

People who are prone to kidney stones may benefit from a diet low in oxalate. However, healthy people who are trying to stay healthy do not have to avoid foods with a high nutrient density just because they are rich in oxalates. Oxalate-rich foods are simply not a cause for concern for most people.

References

https://www.healthline.com/nutrition/oxalate-good-or-bad