Should you worry about oxalates in food?

Wellness culture always has a new food category lined up to fear. Seed oils. Lectins. Gluten (even if you’re among the 99% of people without celiac disease). Lately, spinach, almonds, and beets are getting side-eyed thanks to a newfound awareness of oxalates: naturally occurring compounds often labeled as “anti-nutrients.” The name sounds ominous. But the science? Not so much.

What are oxalates?

Oxalates are natural compounds found in plenty of plants that make it onto your plate. They bind to minerals like calcium, magnesium, potassium, and iron, and slightly reduce their absorption—hence why they’re often referred to as anti-nutrients, says Maddie Pasquariello, MS, RDN, a dietitian based in Brooklyn. (“Slightly” is the key word here, as they don’t automatically cancel out the nutrients in your salad.)

Unless your diet consists entirely of chicken breasts and protein shakes, you’re probably eating your fair share of oxalates every day. Spinach has the highest concentration of them, with 40 times as many oxalates than most other veggies, says Janelle Connell, RDN, a dietitian and the translational science nutritionist at Viome. Other high-oxalate foods include beet greens, Swiss chard, and rhubarb. They also show up in plenty of foods you’d never think twice about, from almonds and raspberries to dark chocolate. That’s what makes things confusing: The list overlaps almost perfectly with foods that get the green light from dietitians and health experts.

Are oxalates harmful?

Like many nutrition villains before them, oxalates have been stripped of context online, making them more feared than legitimately understood. “Many believe that they will block or destroy minerals in foods, which isn’t the case,” Pasquariello says. While they may inhibit their absorption, it’s not in meaningful amounts. And for most people, their gut microbes do a pretty good job of breaking down oxalates before they have a chance to cause problems.

“When certain microbes are present and thriving, less oxalate gets absorbed into your blood and passed on to your kidneys, leaving less raw material behind,” says Connell. From there, your kidneys filter the oxalates and send them out through waste. There’s just one important exception.

Some people need to be more cautious than others when consuming them in large amounts. In susceptible people, excess oxalate can bind with calcium in the urine, forming crystals that can eventually become kidney stones (which affect an estimated 11% of adults in the United States). Calcium oxalate stones are the most common type of kidney stones, says Connell, which makes oxalates worth limiting if you’re already prone to them. The risk compounds if you have low calcium intake, don’t consume enough fluids daily, or have certain gut conditions.

Connell adds that some people lack the specific gut microbes to adequately process oxalates. These include Oxalobacter formigenes, “whose entire job is breaking down oxalate before it gets absorbed,” as well as Lactobacillus and Bifidobacterium (both of which are common in probiotic supplements). Based on Viome’s internal data, roughly a quarter of their customers are at greater risk of oxalate buildup since they lack these microbes. Some people may notice bloating or GI discomfort after eating high-oxalate foods, though symptoms aren’t always obvious.

Should you avoid oxalates?

“For most people with a well-balanced diet, oxalates are not an issue,” Connell says. “Your gut and kidneys are built to handle them, and you excrete the excess in stool and urine.” Pasquariello reiterates that oxalates exist in plenty of healthy plant foods that are highly beneficial for your health. In other words, you shouldn’t begin to second guess your Sweetgreen slop bowl or fear greens like a picky five-year-old.

However, those who are prone to kidney stones—or discover through tests that they don’t process oxalates as efficiently as they should—may want to take a closer look at their intake. “If you learn from microbiome testing that your microbes aren’t efficiently breaking down oxalates in foods, or you’re at risk of kidney stones, the first step is to gradually lower your intake of foods high in oxalates,” says Connell. That said, swearing off oxalates entirely isn't necessary. And considering how many otherwise nutritious foods contain them, it’s not practical either.

For these populations, she suggests pairing high-oxalate foods with a calcium source. Think Greek yogurt with raspberries or spinach in an omelet. “This lets the calcium bind up the oxalates and the body excretes it in the stool rather than absorbing it into the bloodstream,” Connell says. Cooking spinach and other leafy greens can also substantially lower their oxalate content. Pasquariello adds that getting enough calcium and not overdoing animal protein may further reduce kidney stone risk.

The bottom line

While some naysayers liken oxalates to a dietary bogeyman, the truth is that they’re harmless to most people. If you have a history of calcium oxalate kidney stones, consult your doctor or a dietitian to see if you need to modify your diet—whether that’s to reduce oxalates or increase calcium—to mitigate your risk. For everyone else, don’t complicate things. The takeaway isn't to stop eating plants. It’s to stop letting social media convince you they’re secretly bad for you.