So, you had a kidney stone and were given some information about a low oxalate diet. Or, you did your research and you found some information online about oxalate and kidney stones. But, what the heck does a “low oxalate diet” even mean? And, why is that important?
What Is Oxalate?
Firstly, what is oxalate itself? Oxalate is something called a “non-nutrient”. Basically, it is a compound found in many (healthy!) foods that doesn’t provide our bodies something they need. Compare this with a “nutrient” (such as potassium, calcium or a vitamin), which does something good for our body.
Oxalate is primarily found in plant foods. Vegetables, fruits, beans, nuts, seeds and whole grains are most known for having high oxalate levels. Of course, some plant foods have more oxalate in them than others. Oxalate tends to be in very healthy foods!
Oxalate and Kidney Stones
Oxalate is probably most known for it’s role in kidney stones. This makes sense, as about 80% of kidney stones are made of calcium and oxalate. (1)
Calcium oxalate kidney stones are more likely to form with the conditions in your urine are just right. Calcium and oxalate love to bind when:
- There is a lot of calcium in your urine
- There is a lot of oxalate in your urine
- Your urine is very concentrated (aka – you don’t drink enough water!)
- There is too much acid in your urine (pH is too low)
- There is not enough citrate in your urine
Nutrition can play an important role in preventing calcium oxalate kidney stones by modifying each of these urine risk factors.
Beyond Calcium Oxalate Kidney Stones
Although a majority of kidney stones are made from calcium and oxalate, there are many kinds of kidney stones. Most notably, calcium phosphate and uric acid kidney stones are common. (1)
If you have had kidney stones that are NOT calcium oxalate, chances are you do not need to avoid how much oxalate you eat. Avoiding oxalate will not reduce your risk of kidney stones in this case.
This is why it is so important to have your kidney stones analyzed. The type of kidney stone you make should dictate treatment, including the kind of diet you follow for prevention.
If you were not able to have your kidney stone analyzed, a 24-hour urine test will help you and your doctor understand what kind of kidney stone you are prone to making. And, how high your risk is for forming another stone. A 24-hour urine test will measure how much oxalate is in your urine, which will also help you determine if you need to cut back how much oxalate you eat.
Does a Low Oxalate Diet Reduce Calcium Oxalate Kidney Stones?
Surprisingly, no published studies have shown a reduced risk of kidney stones by reduced dietary oxalate. Although we do know that eating more oxalate increases the amount of oxalate in your urine, this only accounts of 30-50% of the variation in urine oxalate.(2) And, many other factors play into kidney stone risk including urine calcium, pH and citrate.
In fact, the DASH diet has been well documented to both reduce the risk of kidney stones and kidney stone risk factors. (3)(4)(5)(6) The DASH diet includes 9-10 servings of fruits and vegetables per day and encourages nuts and seeds – making it fairly high in oxalate. Despite this, people who follow dietary patterns similar to the DASH diet are less likely to have kidney stones. This is likely because the DASH diet impacts many other beneficial kidney stone risk factors such as urine pH, citrate and dairy.
This is not to say that we should throw oxalate out the window. Some people do have very high levels of urine oxalate and avoiding high oxalate foods can reduce their kidney stone risk. But, a low oxalate diet is NOT necessary for everyone with kidney stones.
So, what is a person with kidney stones to do!? The answer lies in kidney stone urine risk factors. Not everyone, even everyone with the same type of kidney stone, has the same urine risk factors.
Individualized Healthy Eating for Kidney Stones: Much More Than a Low Oxalate Diet
To be as effective as possible, healthy eating for kidney stones must be individualized to urine risk factors. Here is a list of common urine kidney stone risk factors. Each of these can be identified with a 24-hour urine test:
- High urine calcium
- High or low urine pH
- Low urine citrate
- Low urine volume
- High urine oxalate
Each of these urine risk factors can be targeted with specific dietary change.
Interestingly, the most common urine risk factor for kidney stones is high urine calcium. Too much salt, protein and added sugar can contribute to high urine calcium.
If you do not have high urine oxalate, then you do not need to follow a low oxalate diet. Instead, you should focus on your urine risk factors for kidney stones.
Inaccurate Kidney Stone Nutrition Info is Rampant
Unfortunately, generic “kidney stone diet” education materials are often given to everyone with kidney stones, no matter what kind of kidney stone they have. Or, what their specific urine risk factors are. In fact, a 2018 study found that information given to people with kidney stones in the Emergency Room may be a common source of misinformation.(7) It is important to follow-up with your doctor and do a 24-hour urine test to understand what healthy eating for kidney stones should be for you.
How to Lower Urine Oxalate
If you do have high urine oxalate, then nutrition can play a very important role in lowering it. But, how much oxalate you eat is only part of the puzzle. Here are 3 steps to lower how much oxalate is in your urine.
Step 1: Get Enough Calcium
For most people, eating enough calcium is the most important thing you can do to bring urine oxalate down to healthy levels.
Calcium and oxalate love to bind with each other. If you eat calcium-rich foods with your meals, calcium will bind with oxalate in your intestine, stopping the oxalate from getting absorbed.
Research has shown that eating enough calcium is more effective at lowering urine oxalate than a low oxalate diet.(8)
For most adults, a goal of 1,000 – 1,200mg of calcium per day is ideal to prevent kidney stones. This is the same amount of calcium that is recommended to the general population.(9)
Eating 3 servings of dairy per day will nearly guarantee that you meet this calcium goal.
Step 2: Eat the Right Amount of Protein
Our liver can make oxalate from protein. So, eating too much protein can increase how much oxalate your liver makes, causing an increase in urine oxalate.(10)
Protein needs are different for everyone. But, a goal of about 0.8 grams of protein per kilogram body weight is a good place to start. This is plenty of protein for most people and is the recommended amount for healthy adults in the United States.(11)
For most of us, meat, chicken, fish and seafood are the main source of protein in our diets. Focus on limiting portion sizes of these foods to 3-6oz. And, limiting these foods to no more than 1-2 meals per day.
Step 3: Reduce How Much Oxalate You Eat
The last step to lowering urine oxalate is cutting back how much oxalate you eat. The good news is that many people can bring their urine oxalate levels down to a safe range by avoiding only the very high high oxalate foods and making sure to get enough calcium.
The very high oxalate foods are:
- Almonds (and almond products such as almond milk, flour and butter)
- Navy Beans
If your urine oxalate levels are still high after avoiding these foods and getting in your calcium, I recommend limiting oxalate to 100mg per day. NOT an “all or nothing” approach. If you focus on avoiding oxalate as much as possible, you will likely limit otherwise very healthy foods, making it difficult to give your body the fiber, fruit, vegetable and other nutrients it needs. This can increase risk of other health conditions like heart disease, cancer, diabetes and even cognitive decline.
Notice that 100mg of oxalate per day is fairly generous. You can “spend” your 100mg however you want! Chances are, you can absolutely enjoy your favorite foods even if they are on the higher oxalate side. Just be mindful of portions. For example, whole grain bread is notorious for being high in oxalate. However, one slice only has around 6mg of oxalate. When you think about a “low oxalate” diet as 100mg of oxalate per day, you have plenty of room to enjoy healthy whole grains!
Incorrect Oxalate Food Lists
You might notice that this high oxalate food list contradicts others you’ve found online. Or, even lists that your doctor gave you. Unfortunately, there is a ton of incorrect information out there when it comes to high vs. low oxalate foods. Oxalate is notoriously difficult to measure, and many of the food studies measured it incorrectly in the past. In addition, one person’s definition of a “high” oxalate food may be different than someone else’s definition.
I recommend using the Harvard Oxalate Food List, as we know the way oxalate was measured for this list was accurate. I also find it useful to stick with one list to avoid the frustration and confusion of trying to piece together other lists with conflicting information.
Low Oxalate Diet and Chronic Kidney Disease
There is some interesting research examining the role oxalate may have in kidney disease. In some cases, high urine oxalate has been linked to increased inflammation and faster progression of kidney disease. (12) In addition, “juicing” and “cleanses” that recommend extremely high amounts of high oxalate foods have been found to cause nephropathy. (13) (14)
However, not all bodies handle oxalate the same way. Some people absorb a lot of oxalate from their food, whereas others do not. Remember that diet oxalate may not even be the biggest contributor to urine oxalate. Oxalate make in the liver can be a big contributor to total body oxalate.
Because oxalate is in so many foods that we know are good for kidney disease, I do not recommend that everyone with kidney disease avoid oxalate. We know that vegetarian diets high in very high oxalate foods such as beans, nuts, seeds, lentils and vegetables can slow the progression of kidney disease.(15)
However, if a 24-hour urine test shows high levels of oxalate in your urine, it may make sense to reduce how much oxalate you eat. Work with your doctor or dietitian to figure out what is best for you!
Oxalate and Polycystic Kidney Disease
However, even among people who have PKD, there are differences in how much oxalate gets absorbed. The best way to know what is best for you is to get a 24-hour urine test. This will assess how much oxalate is in your urine. If urine oxalate is high, working on getting in enough calcium, avoiding large amounts of protein and reducing how much oxalate you eat may help reduce risk of kidney stones and progression of PKD.
But, unless you have high levels of urine oxalate, I do not recommend that people with PKD avoid high oxalate foods.
Other Low Oxalate Diet Conditions
There are claims that a low oxalate diet helps with many different conditions. However, there has been very little research to determine if changing how much oxalate you eat impacts any of these conditions. Therefore, I cannot recommend a low oxalate diet for any of these conditions. In fact, unnecessarily avoiding oxalate could result in a diet pattern that is less healthy and lacking in important nutrients, exacerbating some of these conditions.
- Vulvodynia (17)
- Interstitial Cystitis
- Inflammatory Bowel Disease
- Cystic Fibrosis
- Arthritis and joint pain
- Other Autoimmune Conditions
- Other Inflammatory Conditions
As always, work with a Registered Dietitian who knows your medical history to figure out what is best for you!