See How Spinach Can Damage Your Kidneys

TRANSCRIPT

Spinach has long been praised as a nutritious superfood, but of all leafy greens, it has one of the highest concentrations of oxalates—a kidney-damaging compound. In your kidneys, oxalates can form crystals known as kidney stones, which are notoriously painful.

So, eating too much spinach can really damage your kidneys. But how much is too much? We’ll reveal that in a few minutes. Additionally, most people don’t know that there are simple tips to lower the oxalate content in spinach, making it safer to eat.

In this video, we’ll cover them all.

Before we dive in, please note, all the information in this video is created by real people, thoroughly fact-checked, unbiased, and reviewed by qualified professionals.

What makes spinach bad for your kidneys?

Oxalates in spinach

Let’s talk about why spinach can be bad for the kidneys. Spinach is high in nutrients like vitamins C and K, as well as calcium, iron, and folate (1). Unfortunately, it’s also high in oxalates (2, 3).

What are oxalates? Oxalates, or oxalic acid, are organic compounds found in many plant foods, like leafy greens, nuts, seeds, potatoes, and beans. Of the leafy greens, spinach has one of the highest concentrations of oxalates.

While oxalates are natural food compounds, when they are metabolized, the byproducts can be toxic (4). In addition to dietary sources of oxalate, which account for about 20 to 40 percent of the oxalate in the body, byproducts from the liver, red blood cells, oxidation reactions also release oxalate (5).

A healthy body is designed to excrete oxalate efficiently, so small amounts are not usually harmful. One serving of raw spinach is about 100 milligrams, and experts say that not exceeding this amount per day can help prevent kidney stones (6).

However, in excess, oxalates can cause health problems, especially if the kidneys can’t break them down. Oxalates are metabolized in the liver and then cleared by the kidneys. Yet, when oxalate builds up, it can lead to kidney stone formation and worsen existing kidney diseases (7, 2). People with chronic kidney disease and those who have frequent kidney stones are at increased risk.

In more severe cases of excess oxalates, the inability to break them down may lead to hyperoxaluria, a condition characterized by having too much oxalate in the urine (8). If left untreated, hyperoxaluria could lead to renal oxalosis, where poorly functioning kidneys cause the accumulation of oxalate in other parts of the body. Oxalates can build up in blood vessels, bones, and even organs, causing further complications such as organ damage or bone fractures (9).

While this all sounds dangerous, don’t forget the good news: the body can handle small amounts of oxalates. A healthy digestive system can break them down, and healthy kidneys can excrete them. However, other health factors, lifestyle factors, and dietary factors play a role in how well our bodies eliminate oxalates. Let’s take a look at some of them.

Low-calcium diets

You may have heard that calcium is good for bones. It also binds to oxalate in the intestines, helping move it out of the body through urine. Without enough calcium, excess oxalate can be reabsorbed into the bloodstream instead of being excreted in the urine. The oxalate can then bind to calcium, forming kidney stones (10, 11). When excess oxalates bind to large amounts of calcium, this reduces the availability of calcium for bones. So, getting enough dietary calcium to accompany oxalate-rich foods is important not only for preventing kidney stones but also for maintaining bone density.

About 10 to 15 percent of oxalates are absorbed in the intestines. Diets low in calcium mean that less oxalate becomes bound, so more oxalate reaches the kidneys. Therefore, a higher calcium intake can be beneficial for kidney excretion of oxalates.

Small Bowel Absorption Syndrome

People with small bowel malabsorption syndrome may have increased oxalate absorption because they have limited calcium in their intestines to bind to the oxalates (4).

Dysbiosis

Anyone with dysbiosis, which is an imbalance of good and bad intestinal microbiota, may have trouble breaking down oxalates (4). This is because our gut microorganisms play an important role in metabolizing oxalates. Without the right balance of healthy bacteria, viruses, and fungi to metabolize oxalates, oxalates can accumulate in the body, potentially causing health problems.

Kidney Disease

And, of course, anyone with impaired kidney function, such as those with chronic kidney disease, will have a harder time breaking down oxalates (12). This can lead to hyperoxaluria or renal oxalosis, where oxalates can accumulate in other organs (8).

Okay, that was a lot. Now you might be wondering who is more at risk for kidney problems.

As for kidney disease, anyone can develop it. However, some people are more at risk, like those with diabetes and high blood pressure (13). As for kidney stones, men are also more likely to get them than women (14). Researchers believe this is due to several factors. Men tend to eat more animal protein and eat less dietary calcium than women. Men also generally drink less fluid than women. Testosterone may also play a role in stone formation by increasing oxalate in urine (15). However, it’s important to note that anyone who does not drink adequate fluids is at higher risk of developing kidney conditions.

This does not mean that if you’re a man with high blood pressure or diabetes, you will develop kidney problems. However, knowing your risk factors is important. If you suspect any problems with your kidneys, seek medical attention. Also, let your doctor know if you experience any of the following symptoms (16, 17):

Loss of appetite
Unintentional weight loss
Itchy skin
Frequent urination
Headaches
Fatigue
Nausea
Blood in the urine

Potassium in spinach

Now, oxalates are not the only issue for people with compromised kidney function. Spinach is also high in potassium, an essential mineral found in foods like bananas and avocados (18). Too much potassium can be harmful to people with kidney disease (19) because people with compromised kidneys cannot remove potassium correctly.

In some cases of kidney disease, instead of excess potassium being excreted through the urine, it gets recirculated in the bloodstream. This can lead to hyperkalemia, or elevated blood potassium levels, causing symptoms like an irregular heartbeat, fatigue, and numbness (20).

For individuals with kidney disease, a diet high in potassium can not only worsen the condition but it could also lead to kidney failure (21). Severe hyperkalemia (High potassium level) can cause abnormal heart rhythms and heart attacks, and it can be fatal in some cases (22).

How to enjoy it if you still want to eat spinach?

To protect your kidneys and to prevent kidney stones, you may wonder if you must avoid spinach entirely or if there are workarounds. Spinach is a healthful food that offers many benefits, like antioxidants, phytonutrients, vitamins, and minerals. However, oftentimes those with kidney problems should limit or possibly avoid spinach due to its high oxalate and potassium contents (23). Yet, this may vary from person to person.

Also, don’t forget that it’s not just spinach to consider – other foods may need to be avoided or limited. These foods are high in potassium: asparagus, avocados, potatoes, tomatoes, squashes, oranges, nectarines, kiwis, dried fruits, bananas, and melons. Similarly, these common foods are high in oxalates: rhubarb, canned fruits, strawberries, beets, leeks, summer squash, sweet potatoes, teas, instant coffee, tofu, nuts, and chocolate (16).

This seems like a lot, but don’t worry – many delicious and healthy foods are low in oxalates and potassium (23). You can enjoy foods like peaches, grapes, pears, apples, berries, pineapple, plums, tangerines, watermelon, broccoli, cabbage, carrots, cauliflower, celery, cucumber, eggplant, green beans, lettuce, onion, peppers, watercress, and zucchini. Stick with fresh foods rather than dried or canned options. Also, not all leafy greens are as high in oxalates as spinach – kale, for example, is much lower in oxalates and should be safe for people with kidney problems (24).

Additionally, if you choose to eat spinach, certain cooking methods (like boiling and steaming) have been shown to reduce the oxalate levels (25). However, with potassium, you’ll hear different opinions. Boiling spinach has been shown to reduce the potassium content (25). Keep in mind that this does not apply to all fruits and vegetables (26).

Here is something else you may want to consider if you’d like to eat spinach: ascorbic acid from vitamin C is metabolized into oxalate (27). Taking a vitamin C supplement (or getting too much through your diet) can be harmful if you have kidney problems. Therefore, cutting back on vitamin C may be necessary if you’re planning to include oxalate-rich foods in your diet.

But before consuming spinach, check with your medical provider. Anyone with kidney problems should develop a personalized diet plan with their doctor. Ask your doctor to monitor your potassium and oxalate levels. Also, ask if any high-oxalate or high-potassium foods are right for you and in what amounts.

What can help reduce the risk of kidney stones and oxalate build-up?

Hydration is also important when it comes to preventing kidney stones (11). The kidneys need water to function well, and they help the body utilize water effectively (28).

There are other ways you can support your kidneys besides maintaining a low-oxalate and a low-potassium diet (29). As mentioned, you can help reduce kidney stone formation by drinking enough fluids to prevent stones from forming.

Another thing you can do to encourage oxalate excretion is to get enough of certain nutrients that can help metabolize oxalates. Here are some of them:

Citrate. Citrate comes from citrus fruits such as lemons and grapefruit (30) can prevent stone formation by binding to calcium and removing some of it from the urine (31). It can also bind to calcium oxalate crystals and inhibit their growth.

Magnesium. Magnesium is an essential nutrient that can help inhibit stone formation (32). While many foods contain magnesium, some of them, such as nuts and dark leafy greens, are also high in oxalates (33). So, it may be helpful to speak with your healthcare practitioner to first check your magnesium levels and possibly take a magnesium supplement.

Calcium. Calcium binds to oxalates in the digestive tract before it reaches your kidneys (11). If you plan to eat oxalate-rich foods, pair them with calcium-rich foods, like low-fat cheese, yogurt, or beans (34). As with magnesium, if it’s not possible to get enough calcium in your diet, speak with your practitioner to determine if a calcium supplement is appropriate.

Probiotics. Because dysbiosis can lead to kidney stone formation, anyone with dysbiosis should take a quality probiotic supplement (35). Having a healthy, balanced gut microbiome can help break down oxalates efficiently. In particular, probiotics that contain species of Oxalobacter, Bifidobacterium, and Lactobacillus can help effectively break down oxalates.

Summary

That was a lot of information! So, let’s recap.

Spinach is a healthy superfood, but it may not be healthy for someone who is at risk for kidney stones or who has kidney disease.

While spinach is high in nutrients like iron and vitamin K, it is also high in oxalates – naturally occurring compounds that can be toxic in high amounts. Ideally, calcium binds to oxalates, and the oxalates are excreted.

A high-functioning digestive system with a healthy gut microbiome can properly metabolize oxalates and help facilitate their excretion. Drinking enough fluids can also help prevent oxalates from forming into kidney stones.

However, things like dysbiosis, dehydration, kidney disease, and other digestive conditions can inhibit these processes. Also, vitamin C can be metabolized into oxalates. This means that vitamin C supplements and foods high in vitamin C should be limited or avoided for those who have kidney dysfunction.

Certain vitamins, minerals, and other nutrients can be particularly beneficial for mitigating harm from excess oxalates. These include calcium, citric acid, probiotics, and magnesium.

Oxalates are not the only reason spinach may harm the kidneys—spinach is also high in potassium. Potassium won’t cause problems in healthy kidneys, but it can aggravate existing kidney dysfunction. In people with kidney problems, their kidneys cannot excrete potassium well, which can lead to high levels of potassium in the bloodstream, which can have dangerous implications for heart health.

Because of oxalates and potassium, anyone with kidney problems is generally advised to limit or avoid spinach.

But don’t fret – spinach is only one of many leafy greens. Other leafy green vegetables have lower amounts of oxalates and potassium. If you’re concerned about kidney health, try switching to kale and other whole fruits and vegetables that are safer for your kidneys.

Always check with your doctor before making any dietary changes. Request a thorough workup and discuss any concerns you have about kidney health. And don’t forget to stay hydrated!