Foods High in Oxalates: How Much is TOO MUCH?
What are oxalates?
Oxalate is produced as an end-product of metabolism of vitamin C, as well as of fructose and the amino acids serine and glycine. The body does not use oxalate for any of its processes; instead, it is excreted from the body through the urine or faeces. Even if oxalate intake is zero, it will still be present in the urine as a result of our body’s natural metabolism.
The normal urinary levels of oxalate do not exceed 40mg (or 440µmol) per 24 hours which is mostly associated with men and not more than 30 mg for women. The difference is mainly the larger meal size men tend to consume rather than in actual intrinsic metabolic difference between sexes.
Which foods are high in oxalates?
Oxalate is generally found in plant foods and less commonly in animal products. Almost all plant or plant-based foods have moderate to high amounts of oxalate. The oxalate content is due to the incomplete oxidation of carbohydrates. Some plant foods extremely high in oxalates include, but not limited to:
- Leafy greens – spinach, Swiss chard, kale, collard greens, Brussel sprouts, celery, parsley, endive, beetroot greens, dandelion greens, and turnip greens.
- Root crops – beets, carrots, potatoes, sweet potatoes, and parsnips.
- Nuts and seeds – peanuts, pecans, beans, buckwheat, and poppy seeds.
- Broccoli and okra.
- Apples, apricots, concord grapes, oranges, star fruits, and berries (strawberry, raspberry, blackberry, blueberry).
- Black pepper
- Tea leaves, cocoa, and cocoa products (yes, including chocolates).
The American Dietetic Association, however, admit it can be difficult to determine the exact oxalate content of oxalate-rich foods. The content depends on the part of the plant (stem, leaf, root, or seed), genetic differences across species, the time of harvest, and the condition of the soil. Even the cooking method can also affect oxalate content. For instance, discarding the water used in boiling or steaming is an effective way to reduce the amount of oxalate particularly in leafy greens.
What is hyperoxaluria?
Hyperoxaluria pertains to a condition characterized by excessive amounts of oxalate in the urine which, if left untreated, may lead to severe kidney damage. Oxalosis, a term closely associated to hyperoxaluria, is the term for oxalate deposits in the kidney.
There are four main types of hyperoxaluria – primary, enteric, dietary, and idiopathic. Out of these four, the most commonly discussed are the primary and enteric types. Primary hyperoxaluria occurs when the liver produces excessive amounts of oxalate. It is a rare genetic disease that affects one in every 100,000 to 1 million people. Enteric hyperoxaluria, meanwhile, develops due to the absorption of too much oxalate in the digestive tract. It is typically a result of intestinal diseases and frequent consumption of foods rich in oxalates.
Oxalate is quite familiar for its role in inhibiting the absorption of calcium. When oxalate and calcium combine, the result is an insoluble calcium-oxalate solid crystal. Under normal circumstances, these crystals are very small in size and can be excreted in urine without causing any problems. Kidney stones develop when too much of these crystals form in the bladder. Calcium-oxalate is the most common form of kidney stone, comprising about 75% of reported cases. Hyperoxaluria increases one’s risk of calcium-oxalate kidney stones.
In most cases, a kidney stone is pretty much a one-time thing and usually does not occur again. An individual can lower his chances from developing kidney stones by increasing fluid intake and reducing the amount of oxalate in food. In some cases, a prescription of potassium-citrate tablets may also be necessary. Citrate binds to calcium to form yet another, but a much more soluble kind of kidney stone.
What causes hyperoxaluria?
Digestive disorders that lead to fat malabsorption are the most common cause of hyperoxaluria. When fat binds to calcium, the latter becomes unavailable to bind with oxalate. This results in unbound oxalates that can be easily absorbed in the gut. Disorders that can cause fat malabsorption include:
- Short bowel syndrome, wherein a portion of the bowel is missing (such as in severe Crohn’s disease) or removed via surgery (i.e. bariatric surgery).
- Cystic fibrosis, where fat malabsorption is usually due to pancreatic insufficiency and/or antibiotic treatment.
It is also possible for someone who has a “leaky gut” to suffer from hyperoxaluria. In leaky gut, there are gaps between the cells of the intestinal walls, allowing them to absorb large amounts of oxalates.
Oxalate is an end product of the metabolism of different nutrients, most importantly Vitamin C. The RDA for vitamin C is 90mg and 75mg for males and females, respectively. Taking more than 1000mg of this vitamin per day increases one’s risk for hyperoxaluria (and subsequently, kidney stones) according to a 2004 report from the Health Professionals Follow-up Study.
Individuals at high risk for developing kidney stones should not take supplements containing Vitamin C. But this does not mean they can’t get their daily dose of this vitamin from other sources. Citrus fruit juices, like orange and lemon juice, are rich in vitamin C but they can still be beneficial in preventing kidney stones due to their citrate content.
In the same report by the Health Professionals Follow-up Study, the association between fructose intake, hyperoxaluria, and risk of kidney stones was also discussed. Fructose given intravenously resulted in increased urinary oxalate in both men and women. Interestingly, though, an orally-administered fructose produced the opposite effect – that is, reducing urinary oxalate.
Vitamin B6 Deficiency
Vitamin B6 deficiency could also be a contributing factor to the development of hyperoxaluria. According to researchers, low serum vitamin B6 may cause accumulation of a compound called peroxisomal glyoxylate, which is oxidized to oxalate.
Individuals who love green smoothies may end up with excessive levels of oxalate which, in turn, could possibly lead to kidney stones. Apparently, there are reports of people who develop kidney stones as a result of going on a green smoothie diet.
What health problems are caused by too much oxalate?
The health problems caused by too much oxalates does not end with kidney stones. Aside from calcium, oxalate is also attracted to other molecules like iron. The combination of oxalate and iron called iron (II) oxalate has a major role in gout. Foods rich in oxalate must therefore be avoided by people who are susceptible to, or are already suffering from gout.
It is also possible that the accumulation of oxalate in the body has become so great it gets deposited in other parts of the body. This has led speculations that individuals who have disease/s other than kidney stones might actually be suffering from oxalate accumulation in other tissues.
Enteric hyperoxaluria, in particular, may either cause and/or exacerbate certain diseases like arthritis, asthma/COPD, fibromyalgia, thyroid disorders, vulvodynia (pain in the vulva triggered by touch and pressure), thyroid disease, and a variety of digestive disorders. Hyperoxaluria is also associated with depression and autism.
What is the treatment for hyperoxaluria?
Hyperoxaluria may be managed by switching to a lower oxalate diet. Many individuals have reported some improvement with such a method. But then again, since the oxalate content of food varies, the following tips may help to reduce the effects of oxalate from your oxalate-rich foods:
Boil leafy greens then discard the water – according to studies, boiling a plant allows a significant amount of its oxalate content to be released into the boiling water. Steaming can also remove a decent amount of oxalate from food, but not as much as boiling does. You may also boil or steam stalks or roots to reduce their oxalate.
Eat calcium-rich foods and/or take calcium supplements – take calcium citrate if you have had calcium-oxalate stones before. Calcium binds to oxalate, rendering it insoluble and therefore much harder to absorb in the gut.
Avoid vitamin C supplements – even better, you can just get your daily dose of this vitamin by drinking orange or lemon juice. That way, you are also ingesting citrate, which can help reduce your risk for kidney stones.
Try a probiotic supplement – some bacteria may aid in the degradation of oxalate in the intestines. These include Lactobacillus acidophilus and Bifidobacterium lactis among others. According to studies, taking probiotic supplements after your last meal for the day may help reduce the amount of oxalate in urine by about 33%.
Other important tips are not including too much oxalate-rich vegetables in your green smoothies and drinking plenty of water.
If you suspect that you might be suffering from hyperoxaluria, consult with your health professional as soon as you can. As for children and adolescents, kidney stones are not common among their age so experts advise that they be screened for hyperoxaluria as soon as there are symptoms.