What are Oxalates and Why are They a Concern for Kidney Disease Patients?

By Jessianna Saville, MS, RDN, LD, CSR, CLT

Oxalates are a natural substance in many foods. They bind to calcium during digestion in the stomach and intestines and leave the body in stool. Oxalate that is not bound to calcium travels as a waste product from the blood to the kidneys where it leaves the body in the urine. There are many different types of kidney stones, but 8 out of 10 stones are calcium oxalate stones. If there is too much oxalate and too little liquid in the urine, calcium oxalate fragments create crystals. As the crystals begin to increase in number, they stick to one another to form a larger crystal known as a kidney stone.

Kidney stones are a big concern for those who have or are at risk for kidney disease. The process of stone formation may cause damage to renal tissue, thus decreasing renal function.
Avoiding kidney stones
Diet modification and adequate hydration are two of the most important things you can do to avoid kidney stones. Many people think a low oxalate diet is the most important thing. This is important for many, but there are many other important lifestyle and diet factors that play a bigger role in reducing kidney stones then eating low-oxalate foods. Research shows that following diet/hydration strategies can dramatically reduce the incidence of occurrence and recurrence of kidney stones.
  1. Stay well hydrated with water. Crystals form when there is too much oxalate in too little liquid in the urine. Staying hydrated throughout the day can help prevent stones. If you are on a fluid restriction, talk with your healthcare professional about the maximum amount you can drink.
  2. Incorporate high calcium foods into your diet. Doing so allows the calcium to bind to oxalate during digestion before ever reaching the kidneys. Good choices include milk, yogurt, and canned salmon. If you are already restricting dairy products for phosphorus control, seeking the help of a RDN is best.
  3. Keep your salt and sodium intake low! Researchers are not exactly sure why a high sodium diet causes more stones. One thought is that a high sodium diet triggers a mechanism that increases water reabsorption in the body and, thus, produces more concentrated urine. More concentrated urine means more stones. Therefore, limiting how much sodium you eat can also play a role in decreasing the risk of kidney stone formation.
  4. Limit intake of any food or beverage with added sugar and other sweeteners, such as high fructose corn syrup. Examples include soda, candy, sweetened tea, coffee, or energy drinks. There are many thoughts on why this may help with kidney stones. There has not been one large study to validate this claim.  However, since it doesn’t hurt and very well may help with kidney stone formation, it is worth the effort to start eliminating added sugars from the diet.
  5. Finally, moderating protein intake may lower the chance of stone formation. This does not mean you have to cut out protein in the diet. Focusing on normal portions at meals (the size of deck of cards) or having some vegetarian meals can help reduce the risk of kidney stones. 
  6. Eliminate excessive intake of high oxalate foods.

What foods are high/low in oxalate?

If you have a history of kidney stones, limiting oxalate-rich foods is a good way to lower your chances of forming another kidney stone. This is not the most important part of avoiding kidney stones, but is an important piece to consider. Foods high in oxalate include nuts and nut butters, especially almonds, and various vegetables, such as beets and beet greens, rhubarb, and spinach.

Diet and hydration are key areas to address to reduce kidney stones. Everyone is different and at different stages of kidney disease. Working with a registered dietitian nutritionist specializing in kidney disease can be helpful in making successful changes at eliminating kidney stones.


About the author:

Jessianna Saville, MS, RDN, LD, CSR, CLT is a  board certified renal nutrition specialist and registered dietitian licensed in the state of Texas.  She works with people with early stage kidney disease to help slow progression of the disease through dietary modification. She currently blogs about renal nutrition at www.KidneyRD.com where she loves to showcase beautiful, renal-friendly food.  She feels passionately about the role nutrition therapy plays in kidney disease to improve quality-of-life, reduce hospitalization, and slow progression to dialysis.  In her spare time she enjoys running, exploring new places with her husband and two children, and trying to make her garden grow.


Date Reviewed: 09-05-2018