Oxalates: How healthy greens can sometimes be bad news for your kidneys


Last Updated October 11th, 2019

Oxalates and kidneys

Kidney stones in the form of calcium oxalate amount to 75% of the prevalence of kidney stones by the USA’s National Health And Nutrition Examination Survey (NHANES) during 2007–2010. Vegan based diets involve plant-based foods such as legumes, spinach, etc. Some of these veggies also contribute to the formation of calcium oxalate. These foods contain oxalic acid (or oxalate). Excess oxalate can give rise to kidney stones. Explore more about oxalate and how food sources affect kidney stones formation.

Oxalate – Understanding more about this compound

sodium chloride kidneysOxalate is a compound found in many plants (spinach, kale, etc.). This compound is found in few amounts in animal-based. Oxalate is rich in vegetables such as sweet potato, spinach, broccoli, carrots, beets, green Swiss chard, kale, turnip greens, rhubarb, etc. Protein metabolism, vitamin C metabolism, intake of fructose in large amounts, etc., result in oxalate formation.

Oxalate is neither utilized nor broken down by the body. It is simply evacuated from the body via feces and urine. Once oxalate is consumed via food, it can bind to minerals such as calcium to form calcium oxalate, or bind to iron to form iron oxalate. Oxalate levels of more than 45 mg/day increase the probability of calcium-oxalate kidney stones. Those who have a sensitive or delicate health system will be more prone to the risk of kidney stones or other related disabilities.

Role of oxalate in kidney stone formation

In general, the urinary tract contains small amounts of calcium and oxalate in un-dissolved form. In some individuals, there are scenarios where they bind to form calcium oxalate crystals leading to kidney stones. This is seen in cases where the urine volume is lower and the oxalate amounts are high.

Small stones will not be problematic and get excreted off into the urine. Accumulation of the larger ones, are painful and can result in bloody urine as they pass through the urinary tract. There are other kinds of kidney stones such as uric acid, calcium phosphate, etc., but calcium oxalate kidney stones occur more commonly. This is why patients are advised on a low oxalate diet. For those with high oxalate levels, the doctor prescribes a low oxalate diet (<50 mg/day).

Formation of calcium oxalate kidney stone formation

Oxalate is naturally produced in the body via natural biochemical reactions. Food is used for energy and nourishment. Post-extraction of the required agents, your body will throw away the waste via urine. Urine contains waste products.

If the levels of these waste products are more and the liquid volume is low, then there are more chances that crystals will be formed. These crystals clump together to form kidney stones. If the oxalate levels are more in the urine, then during the process of urine formation, the excess oxalate will bind to the calcium to form calcium oxalate crystals.

Oxalate absorption in your body is influenced by your gut

You need to know that your gut is lined with useful bacteria that aid in digestion, nutrient absorption, immunity, and waste removal. The gut bacteria disintegrate the oxalate before it prevents any mineral absorption.

Oxalobacterformigenesis a type of beneficial bacteria living in the gut. This bacteria makes use of oxalate as a fuel source. This lowers oxalate absorption in the body. Sadly, most individuals have low levels of this bacteria in their gut. This can be because of treatment with antibiotics.

Overall, those who are on antibiotics, have undergone surgeries, or have digestive ailments (such as inflammatory bowel disease, etc.), will have high oxalate levels in the urine.

Influence of beverages on kidney stones

Research conducted by the Harvard School of Public Health has enlisted the beverages and the manner in which they influence the kidney stone formation.

  • Beverages such as decaffeinated coffee, tea, regular coffee, red wine, beer, orange juice, etc., decrease the incidence of kidney stones.
  • Liquor, artificially sweetened cola, apple juice, artificially sweetened noncola soda, grapefruit juice, whole milk, water, tomato juice, skimmed milk do not show much effect.
  • Beverages such as sugary noncola soda, or cola, punches, etc., increase the incidence of kidney stones.

Regulation of oxalate by the intestinal bacteria

A study in 2013 reported that Oxalobacterformigenes does not minimize the oxalate absorption into the body. It enhances oxalate secretion into the intestine and thus lowers the oxalate levels in the blood. People with high oxalate intakes can compensate by increasing the amount of oxalate degrading bacteria.

Can probiotics help in such cases?

Apart from Oxalobacterformigenes, there are other bacteria such as Eubacteriumlentum, Lactobacillus acidophilus, Enterococcus faecalis, etc., that metabolize oxalate in the blood. There are companies working on formulating probiotics that contain these types of bacteria.

A research study was done on this probiotic mixture of about 800 billion bacterial dosages was administered once a day. This was done for 4 weeks. This minimized the oxalate reduction by about 33%.

Ways to lower oxalate levels

Kidney stones patients are generally asked to indulge on a low oxalate intake.

  • You can include animal and plant-based nourishing foods.
  • You can also consume oxalate-rich vegetables by boiling them. The oxalate content can be lowered by about 90% upon boiling.
  • Make sure you drink lots of water (at least 2 liters per day). Water intake improves the urine volume thereby minimizing the kidney stone problem. It is vital to produce about 2 and a half liters of urine per day.
  • Include calcium based foods because calcium binds to oxalate and prevents oxalate absorption into the body.

What foods are low in oxalate?

The following are the list of foods that are rich in calcium and low in oxalate.

  • Bok choy (Chinese cabbage)
  • Plain yogurt
  • Broccoli
  • Cheese
  • Canned fish with bones

Oxalate impedes mineral absorption

Oxalate is named as an anti-nutrient because it hampers with mineral absorption. For example, Spinach contains both calcium and oxalate. Oxalate reduces calcium absorption into the body. It binds to the minerals present in the gut and prevents their absorption into the body.

Also, some foods contain fiber along with the presence of oxalate. This will minimize mineral absorption even more. Absorption of iron and zinc is hampered by oxalate as well. If you are consuming spinach, try consuming calcium based foods such as yogurt along with it. This oxalate in spinach will not affect the calcium absorption from yogurt.

Is it advisable to avoid oxalate-containing foods?

Not necessarily. Those who have a sensitive health system or have kidney stones can benefit a great deal from a diet low in oxalate content. Healthy people need not be so stringent on oxalate-rich foods as they are highly nourishing as well.

How to manage with oxalate-rich foods?

It’s simple. Just include a blend of oxalate foods with other calcium-rich foods such as soybeans, collards, okra, oatmeal, etc.

How can I lower my chances of forming calcium oxalate stones?

  • It is important that you drink a good amount of fluids. This will lower the chances of crystal formation.
  • Do not consume excessive amounts of proteins as this can aid in the kidney stone formation.
  • Consume less amount of sodium (salt). Too much sodium results in calcium surge in the urine. Too much calcium in the urine can result in the formation of new kidney stones.
  • Make sure you do not overdo with respect to vitamin C supplements. Too much vitamin C supplements mean too much oxalate in urine.

Is it good to refrain from oxalate-rich foods?

If you cut down on high oxalate foods, then, your chances of kidney stones will become less. On the contrary, you will also deprive your body of vital nutrients.

Does oxalate result in any other problems?

There are some claims on increased oxalate levels being associated with autism. Autism is a hereditary disorder where the child has inabilities associated with social interaction and communication.

  • Other scientists also claim that oxalates may be associated with vulvodynia (severe pain around the vagina).
  • More research is needed as the existing ones are inconclusive with respect to high oxalate levels.

Oxalates: In a nutshell

Oxalate is naturally present in nutrient-rich foods such as spinach, kale, turnip greens, cocoa powder, etc. They are also naturally synthesized in the body via biochemical reactions. Oxalate lowers the mineral absorption and can also result in the formation of kidney stones.

Factors such as too much protein or inadequate hydration also contribute to kidney stone formation. Curtailing on greens will only give you a nutrient deficit. So, to avoid kidney stone formation, consume calcium-rich foods along with greens and also, drink a good amount of water to increase the urine volume.

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