What are Oxalates and Should You Avoid Them?
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What are Oxalates and Should You Avoid Them?

If you're concerned about kidney disease or kidney stones you may want to watch out for high oxalate foods like kale, cauliflower, rhubarb, and blueberries.

Oxalates are sometimes called anti-nutrients, primarily because they bind to minerals in your body. 

You may have heard that avoiding oxalates is a good idea, especially for kidney stone prevention. However, the oxalate story is a bit more complicated, and understanding what oxalates are, and what their place is in your diet is important.  

The oxalate content of foods varies widely, and in many foods, they are minuscule or nonexistent. 

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However, there are certain conditions where you may benefit from understanding the oxalate level of the foods you eat. This, along with the amount of calcium you consume, can make a difference in how your body absorbs these “anti-nutrients”.

What Are Oxalates?

Oxalates, also called oxalic acid, are natural compounds that are found in a wide variety of plant foods. They’re often referred to as “anti-nutrients” due to their affinity to bind minerals. 

So why are there anti-nutrients in plants? 

Just like the human body has its own immune defense — plants need a defense system of their own. These anti-nutrients help protect plants against predators like animals, insects, and harmful bacteria. 

Without the help of oxalates and other anti-nutrient compounds, we may not have the abundance of plant foods available that we do today. And although oxalates do bind to some minerals in your body, they can also be broken down by your gut bacteria[*]. 

There are rare conditions where oxalates can build-up in your body, causing stress to your kidneys and liver. However, these conditions are mostly caused by endogenously produced oxalates — not the kind you find in your food[*].

With that being said, there are certain circumstances where following a low oxalate diet could be helpful. 

How Oxalates Are Processed In Your Body

Typically, when you consume a food rich in oxalates, they will bind to minerals in your digestive tract and be eliminated from your body. While this is not great news for your minerals (most frequently calcium), it’s a safer fate for you then if oxalates are absorbed unbound.

In the instance where oxalates remind unbound, they will then be absorbed by your body and sent to your kidneys to be removed as a waste product. If this process goes smoothly, then all is well, and there is no need for concern. 

However, due to oxalates affinity for minerals, they may bind to calcium in your kidneys. This is where things get tricky because oxalates and calcium can build-up and eventually form calcium oxalate kidney stones. This issue becomes heightened when you don’t drink enough fluid to properly move compounds through your kidneys[*].

What Causes Oxalate Build-Up?

Specific strains of gut bacteria help to metabolize oxalates, and in some people may even reduce the risk of kidney stones. In one study, researchers found that people with high levels of Oxalobacter formigenes, a gram-negative bacteria had a 70% decreased risk of developing kidney stones[*].

On the other side of the coin, antibiotics can lead to diminished levels of this type of bacteria. Without Oxalobacter formigenes to help break down oxalates, you may experience a build-up[*].

The health of your digestive tract is closely related to your risk for developing kidney stones. This is likely due to the fact that when digestion is running smoothly, oxalates can be broken down and eliminated properly. However, when there are digestive issues present, the risk for oxalate build-up increases.

This is true for people with inflammatory bowel diseases, as well as people undergoing gastric bypass. Any type of alteration to your gut functionality can be a risk factor for oxalate build-up[*][*].

Are Kidney Stones Genetic?

It’s estimated that 40% of people who form kidney stones have a family history. If you do carry this trait, you’ll likely start forming stones early in life. 

Genetics come in specifically with calcium-oxalate stones in hypercalciuria as well as Primary hyperoxaluria[*].

Hypercalciuria is a condition where excess calcium ends up in your urine. This calcium excretion results in excess calcium moving through the kidneys, increasing the likeliness for binding with oxalates. It’s believed that hypercalciuria may be caused by various gene defects. 

It should be noted, however, that these defects are relatively rare.

Primary hyperoxaluria results in the production of high amounts of oxalate in your body. This is caused by a gene mutation which results in a defect in your liver enzymes. Primary hyperoxaluria is passed on genetically within families. 

The excess oxalate is then passed on to be excreted through your kidneys, which can result in calcium-oxalate stones. In severe cases, kidney disease may develop, and liver or kidney transplant may be necessary[*].

Although genetics can certainly play a role, other risk factors for kidney stones include:

  • Not consuming enough calcium
  • Dehydration
  • Eating foods high oxalates
  • Too much sodium intake
  • Digestive disease
  • Metabolic syndrome and diabetes

High-Oxalate Foods

There are a handful of high oxalate keto-friendly foods that you should watch out for. However, many foods high in oxalates won’t be found in abundance in a balanced keto diet.

High oxalate foods[*]:

Vegetables:

  • Beet greens
  • Eggplant
  • Collards
  • Beans
  • Spinach
  • Kale
  • Swiss chard
  • Leeks
  • Sweet Potatoes
  • Soy beans
  • Tofu
  • Wheat bran

Fruit:

  • Blackberries
  • Blueberries
  • Grapes
  • Currents
  • Raspberries
  • Rhubarb
  • Figs
  • Grapefruit
  • Tangerines
  • Kiwis

Beverages:

  • Beer
  • Black tea
  • Coffee
  • Chocolate milk
  • Grape juice
  • Soy milk

Starch:

  • Amaranth
  • Buckwheat
  • Grits
  • Cereal bran
  • Rye
  • Wheat
  • Taro
  • Brown rice

Other:

  • Yogurt
  • Flaxseeds
  • Sunflower seeds
  • Chocolate
  • Nuts (cashews, almonds, walnuts)
  • Nut butters

Low-Oxalate Diet

If you’ve had kidney stones in the past, your risk for having future occurrences goes up 50%. In addition, if you’re experiencing any digestive issues, your risk for oxalate build-up also increases[*].

In both of these cases, you may want to consider a low-oxalate diet to mitigate any potential stone formation. 

To follow a low oxalate diet, you will not only want to reduce high oxalate foods but also focus on getting more low-oxalate foods into your meal plans. 

13 Low-Oxalate Foods (That Are Also Keto!)

Here is a list of low-oxalate, keto-friendly foods to focus on[*]:

Vegetables:

  • Cucumber
  • Cabbage
  • Broccoli (moderate)
  • Cauliflower
  • Zucchini
  • Artichoke (moderate)
  • Mushrooms
  • Avocado
  • Peas
  • Asparagus (moderate)
  • Brussels sprouts (moderate)
  • Carrots
  • Celery

Animal Protein:

  • Beef
  • Bacon
  • Fish (except sardines)
  • Ham Lamb
  • Pork 
  • Poultry
  • Shellfish

Dairy:

  • Cheese
  • Buttermilk
  • Milk
  • Butter

Beverages:

  • Green tea
  • Herbal tea
  • Oolong tea
  • Lemon juice
  • Buttermilk
  • Wine

In addition to the specific foods listed, there are other factors that can help to contribute to a low-oxalate diet.

Watch Your Vitamin C Intake

Oxalates can be found in your diet, but your body also produces them endogenously. One pathway for oxalate production is through the metabolism of vitamin C.

Research shows that people who take 1,000mg of vitamin C a day may be at an increased risk for kidney stones. One study even reported a 2-fold increase in risk with this level of supplementation[*].

Keep in mind that 1000mg a day is a very high dose of vitamin C, so the focus shouldn’t be on avoiding foods that contain vitamin C, simply avoid high dose supplements. 

Increase High-Calcium Foods 

Since calcium is one of the minerals that bind to oxalates, you can use calcium-rich foods as a way to naturally decrease the number of oxalates that get absorbed by your body. 

In fact, calcium plays such a vital role in overall health that you should keep these foods in mind whether you’re trying to avoid oxalates or not[*].

Keto-friendly, calcium-rich foods:

  • Milk
  • Yogurt
  • Sardines
  • Salmon
  • Cottage cheese
  • Turnip greens
  • Kale
  • Chinese cabbage
  • Bok choy
  • Broccoli

Stay Hydrated

As mentioned before, oxalates leave your body from one of two pathways; elimination in your digestive tract, or as waste through your kidneys.

If oxalates make it past your digestive tract and into circulation, then it’s up to your kidneys to remove them as waste. Problems occur when your kidneys can’t get the job done, and oxalates build up inside the kidneys.

One way to support your kidneys is to stay hydrated. The more water you take in, the more fluid gets to travel through your kidneys, pulling out impurities along the way. 

If you sweat a lot, do hot yoga, go to a sauna, or lose significant amounts of water in any other way, take that water loss into account as well[*].

Reduce Sodium Intake

Along with reducing oxalate-rich foods, you’ll also benefit from reducing your sodium intake. 

When it comes to kidney stones, the name of the game is decreasing the amount of minerals traveling through your kidneys. And when you consume sodium, it needs to be excreted through your kidneys. 

Although sodium itself doesn’t cause form kidney stones, it pulls more calcium into your kidneys as its being eliminated. This results in an increased level of potential of stone-forming minerals hanging around for oxalates to bind to[*].

Who Should Avoid High-Oxalate Foods?

As mentioned above, if you’ve experienced kidney stones in your past, your risk for developing future stones increases by 50%. Therefore, if you have a history of kidney stones (specifically oxalate-calcium stones), you may want to watch your oxalate intake[*]. 

Another group of people that may want to be on oxalate alert are those with digestive issues. This can range from inflammatory bowel disease to recent surgery like gastric bypass[*]. 

The reason for this is due to an imbalance in gut bacteria. When your digestion is off, or you’ve had surgery that affects your digestive tract, things aren’t going to run as smoothly. Since the breakdown of oxalates depends partially on your gut bacteria, any imbalance in your microbiome may affect oxalate absorption[*]. 

Finally, if you have a family history of kidney stones, then following a low-oxalate diet may be a good idea. Aside from the genetic conditions hypercalciuria and primary hyperoxaluria, a family history of kidney stones also increases your chances of developing stones. In fact, it’s estimated that 40% of people with kidney stones have a family history[*].

Takeaway

Oxalates can be found in a wide variety of foods. While the term ‘anti-nutrient” may sound off-putting, for most people these dietary compounds aren’t so bad. 

Most of the oxalates you consume in your diet are actually eliminated in your digestive tract, never making it into circulation. This is due to the fact that they either bind to minerals and get excreted, or are broken down by gut bacteria. 

However, if they do make it into circulation, your kidney comes in to remove them as waste products. This only becomes a problem in certain genetic conditions, or if you are prone to kidney stones.

If you know of family members that have had kidney stones, or if you’ve experienced them in the past you may want to watch your oxalate intake. In addition, keep your diet rich in calcium, low in sodium, and make sure to drink plenty of water.

Due to your digestive systems key role in oxalate elimination, if you have digestive issues, you may want to watch out for oxalates as well.

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