Oxalates are compounds found in many foods, including fruits, vegetables, grains and nuts. They're also naturally produced by the body.
The problem: Oxalates can bind to calcium and other minerals in the gut, preventing their absorption and compounding to create solid masses in the kidneys, aka kidney stones. In particular, a high-oxalate diet combined with low urine output seems to be the perfect storm for kidney stone formation, according to a July 2015 study in Clinical Nutrition Research.
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For this reason, people who have a history of kidney stones may be advised to limit their intake of foods high in oxalates. Still, it's important to note that most people can safely enjoy moderate amounts of oxalate-containing foods without any negative effects.
A low-oxalate diet typically allows for less than 50 milligrams of oxalates per day. But many sources disagree about the oxalate content in different foods, according to a September 2014 study in Urology. Regardless, a low-oxalate diet is rich in proteins, dairy, and low-oxalate grains, fruits and vegetables. Less than 10 milligrams per serving is considered a low-oxalate food.
Does Alkaline Matter?
The alkaline diet is not evidence-based because the food we eat can't alter pH significantly. Our body tightly controls this through homeostasis and both acidic or alkaline foods do not cause it to vary much.
Simply put: The body regulates pH levels independent of diet changes.
Our pH is tightly controlled by our lungs and kidneys, and it remains in the range of 7.3 to 7.4 for our survival. But our urine's pH will vary as the kidneys work to excrete waste that helps maintain our body's pH internally, per the University of California San Diego.
The principle behind the alkaline diet is that the kidneys may not have to work as hard to keep the body's pH balance in check. But, the actual pH of foods does not have a direct effect on the body's pH. The food we eat affects the kidneys and the "potential renal acid load" (PRAL) is most important for pH balance, per the University of California San Diego.
Plus, acidic foods do not create an acidic environment in the body or lower your pH. For example, highly acidic foods like citrus are actually considered to be alkaline due to their low renal acid load.
Low-Oxalate, High-Alkaline Foods
Below, find a list of low-oxalate foods along with their oxalate count per serving, from the University of California Irvine.
1. Radishes: 0 mg (per 10 radishes)
This root veggie comes in a variety of colors, shapes and sizes ranging from oval and red to white and long or purple and round. Radishes contain low levels of oxalates, and they're also low in calories, are excellent sources of vitamin C and good sources of calcium. Daikon radishes, in particular, are good sources of potassium and copper.
2. Lemons: 1 mg (per 1 lemon wedge)
Lemons and limes are highly alkalizing foods, despite their high citric acid content, according to the University of California San Diego. Both also have a low oxalate content, so people prone to forming oxalate-containing kidney stones can enjoy lemons. Lemons are an excellent source of vitamin C, with 34 percent of our daily value per fruit, and they provide small amounts of potassium, B vitamins and antioxidant flavonoids, per the USDA.
3. Cantaloupe: 1 mg (per ¼ melon)
Cantaloupe is another highly alkaline-forming, low-oxalate, low-calorie, nutrient-dense food — 1 cup contains 56 calories, 90 percent of the recommended daily allowance of vitamin C and 129 percent of the recommended daily allowance of vitamin B6, according to the USDA. Cantaloupe is also an excellent source of carotenes and potassium. The nutritional profiles, low oxalate levels and alkalizing effects of honeydew melon and watermelon are comparable to cantaloupe.
4. Watermelon: 1 mg (per 1 slice)
Watermelon is naturally high in water, potassium and fiber and very low in oxalates. Similar to other types of melon, watermelon is low in calories and packed with nutrition. Watermelon is a good source of vitamin C, containing 20 percent of the daily value per cup of cubed watermelon.
5. Raisins: 3 mg (per 1 tablespoon or one small snack box)
While raisins are low in oxalates, grapes are even lower. Per 1/2-cup serving of grapes, you'll get 1 milligram of oxalates. While green grapes are low in oxalate, red and purple grapes have higher oxalate levels.
Raisins from any type of grape, however, have low oxalate levels and are one of the most highly alkaline-forming foods. Raisins are also very good sources of dietary fiber, antioxidants and vitamins B1 and B6.
6. Cucumber: 4 mg (per one medium cucumber)
A cucumber's alkaline-forming nature is due in part to its high water content. Cucumbers are an excellent source of silica, a trace mineral that promotes healthy skin and strong connective tissue. Choose organic cucumbers whenever possible — pesticides reduce the vegetable's alkalizing effect.
7. Avocados: 4.75 mg (per ¼ avocado)
Avocados contain a low amount of oxalate and are highly alkaline-forming in the body. Like most foods, portion size matters. A whole avocado has around 19 milligrams of oxalates, which absolutely categorizes it as a high-oxalate food. However, a single serving of avocado is 1/4 of the fruit. So if you stick to enjoying just a 1/4 avocado, it can be part of a low-oxalate diet.
Avocados are alkaline when tested directly for pH, but when you consider how food affects the body's pH, we know that alkaline foods do not make the blood more alkaline.
Bonus: Avocados are also an excellent source of calcium, magnesium, potassium, dietary fiber, vitamin E, B vitamins and heart-healthy essential fatty acids.
Other Low-Oxalate Vegetables
Soaking your vegetables in water before cooking helps pull out oxalates by leeching them into the water. But if you do this, you may also lose other water-soluble nutrients like potassium and phosphorus.
Include these low-oxalate veggies in your diet:
- Bok choy
- Green pepper
- Brussels sprouts
Other Low-Oxalate Fruits
In addition to those mentioned above, these fruits are naturally low in oxalates:
Low-Oxalate Protein Sources
Most sources of animal-based proteins are low in oxalates or contain zero oxalates because oxalates are found in plant foods. Vegetarian sources of proteins like nuts, beans, and legumes are higher in oxalates.
Include the following low-oxalate proteins in your diet:
- Red meat
- Fish (with the exception of tuna)
Low-Oxalate Grains and Starches
Flours made from whole grains are a good source of complex carbohydrates, dietary fiber, vitamins, minerals and phytonutrients. But some flours contain higher levels of oxalates than others. Here's a list of low-oxalate grains that are also high in fiber and other nutrients:
- Barley flour
- Oat bran
- White rice
Coffee, milk, water and many fruit juices are considered low-oxalate drinks, according to the University of California Irvine.
How to Get Rid of Oxalates
- Drink plenty of water: Water helps flush out oxalates and prevent build-up that contributes to kidney stones, according to a July 2015 study in Urolithiasis.
- Reduce your sodium intake: A high-salt diet may be one factor that is associated with increased kidney stones, according to a March 2012 study in the Journal of Urology.
- Eat foods high in calcium: Emphasizing high-calcium foods in your diet helps bind oxalates and helps excrete them, according to an October 2013 study from the Journal of Urology.
- Use vitamin C supplements cautiously: Ascorbic acid, the main ingredient in many vitamin C supplements, has been shown to convert into oxalate at high doses of over 1,000 milligrams, according to a March 2016 research study in Urolithiasis.
Are There Any Risks to Following a Low-Oxalate Diet?
Foods high in oxalates are highly nutritious foods like whole grains, fruits, and vegetables. Unless you have been advised by a doctor, you may have very little need for a low-oxalate diet.
When following a low-oxalate eating plan, be sure to include a variety of foods to meet your nutrition needs. Vegan and vegetarians are especially at risk for not meeting their needs as they may need to cut out premium sources of protein from nuts, grains and beans.
To prevent nutrient deficiencies, ensure that a low-oxalate diet is medically necessary for you, and work with your healthcare team to build an eating plan that works for you.