Oxalates & Kidney Stones – What You Should Know

This question has come up now and then in the Ask the Nutritionist forum so we decided to write a post about it.

The Issue: Some people are concerned that they may develop kidney stones from consuming high oxalate foods.

What is an oxalate and what is it found in?
Oxalic acid is a naturally occurring colourless organic crystal that is found plants. Foods high in oxalic acids include spinach, chard (silverbeet), watercress, leeks, okra, purslane, parsley, beets & the leaves (beetroot), cacao, nuts such as almonds and cashews, buckwheat, some fruits such as starfruit, rhubarb, plums, figs, most berries and some pulses. Most of the foods that contain oxalates are very important for good health. The root and leaves of rhubarb contain dangerously high concentrations of oxalic acid and should not be consumed raw.

Many charts show varying levels of oxalic acid in vegetables, fruits and other plant based foods. It has been shown that growing conditions will affect the amounts of oxalic acids found in plant foods.

Oxalic acid has been shown to bind with calcium and other minerals in the intestines and form an insoluble complex (oxalate) that is excreted via the stool (at least 70-90%), while research studies confirm the ability of oxalic acid in foods to lower availability of calcium and other minerals, the decrease is relatively small. This is also outweighed by the fact that there is so much more calcium, magnesium and iron in oxalate rich vegetables like spinach than the average vegetable in the first place that there will still be plenty of these minerals available to be absorbed!

It is also suggested that the body adjusts its natural manufacture of oxalic acid in response to fluctuating dietary oxalic acid intake. This study and others support the small effect that oxalic acid containing foods have on oxalate urinary excretion. Only spinach, almonds and peanuts caused a small increase in urinary oxalate excretion.

It is now generally believed that the body can dispose of oxalic acid at even relatively high dietary quantities without trouble. Trouble arises for people who may have a genetic predisposition that impairs their bodies’ ability to process oxalic acid, so they may need to regulate their intake of it.

Some studies suggest that people with a history of heavy or recent antibiotic use may be at much greater risk from dietary oxalate. Many antibiotics can kill the flora that degrades oxalate such as oxalobacter, and lactobacillus acidophilus and bifidus. Oxalobacter is a human intestinal bacteria that can reduce the urinary oxalate concentration following an oxalate load.

Those with kidney disorders, gout, rheumatoid arthritis, or certain forms of vulvodynia are typically advised to avoid foods high in oxalic acid. For a normal healthy person developing kidney stones from a high volume of oxalic acid in foods is very unlikely.

Since dietary oxalate accounts for only 10-15% of the oxalate that is found in the urine of individuals who form calcium oxalate stones, many researchers believe that dietary restriction cannot significantly reduce risk of stone formation.

Factors that increase the incidence of kidney stones:
• Soft drinks, due to their phosphoric acid content, they reduce citrate levels in the urine, thus increasing the risk of stone formation;
• Processed foods particularly high in salt;
• Excess sugar consumption;
• High animal protein diets have been associated with increased incidence of kidney stones;
• Excess cadmium increases the conversion of vitamin C into oxalic acid. This can be a problem for people exposed to high levels of cadmium in the diet, in the workplace, or through smoking.

What do if prone to kidney stones:
• Drink plenty of water – more than 8 cups of water daily, the urine should be as clear as water;
• Consuming a diet rich in potassium, magnesium and calcium – vegetables and plant based foods are high sources of these essential minerals. High levels of calcium are shown to be protective against the urinary excretion of oxalates due to intestinal binding with calcium;
• The consumption of fruits and vegetables increases urinary citrate, an important inhibitor of calcium stone formation;
• Lemon Juice: Including this in juices and in water on rising, raises citrate levels in the urine, which may offer protection against kidney stones. Studies also indicate other high potassium citrate juices such as grapefruit, tomato and lime are shown to reduce the incidence of kidney stones. Juice up!
• There is some preliminary evidence that the administration of probiotics can affect oxalic acid excretion rates;
• Vitamin B6 (or pyridoxine), is used to treat people with primary hyperoxaluria, a severe inherited disorder;

Oxalic acid consumption, on the whole, should not be a concern for the average person. In persons that may have trouble metabolising oxalates it would be advisable to reduce the very high oxalate containing foods.

Looking at the factors that increase and reduce the incidence of kidney stones; a Reboot makes perfect sense by including plenty of mineral and citric acid rich juices and meals and following the simple eating guidelines after the Reboot.