Here is Why Smoothies May Hurt Your Kidneys

Taking a smoothie is a great way to start the day. Smoothies give a healthy dose of antioxidants, vitamins, and minerals, positively improving your health. However, adding certain ingredients in higher proportions can provide minerals and other compounds in quantities exceeding the daily recommended intake, overworking the kidneys and affecting their health.

High Oxalate Levels in Smoothies

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People taking green smoothies have a higher risk of developing kidney stones. The most common ingredients for making these smoothies, such as spinach, fresh parsley, watercress, Swiss chard, purslane, rhubarb, and kale, have relatively high levels of dietary oxalate.

Oxalates are naturally occurring compounds in specific foods. The body usually excretes them via the kidneys and in the urine. It also eliminates a proportion of these substances in feces once they combine with calcium in the stomach to form calcium oxalates.

Taking foods rich in oxalates without adequate calcium levels significantly increases your risk of developing calcium-oxalate kidney stones. Theoretically, having insufficient calcium levels in the diet makes oxalate available for absorption. It is then transported to the kidneys for eventual removal through the urinary system. This excess oxalate is broken down into oxalic acid, which reacts with calcium to form calcium oxalate crystals. These crystals grow in size over time, turning into kidney stones.

Different types of kidney-friendly smoothies in glass gars

High Potassium Levels in Smoothies

Oxalates are not the only dietary components that cause kidney problems in those taking smoothies. Some ingredients added to smoothies, such as bananas, dragon fruit, oranges, muskmelon, avocado, tamarillos, and spinach, have high levels of potassium that make them bad for your kidneys.

Excessive amounts of this mineral can present a problem for people who have kidney disease. They can overwork the kidneys and subsequently lead to hyperkalemia if the body cannot eliminate the surplus. Consequently, hyperkalemia can cause life-threatening complications or, worse, death.

High Phosphorous Levels in Smoothies

Smoothies also often contain high phosphorous levels. Excessive amounts of this mineral lead to an abundance of phosphate ions that combine with calcium, leading to the formation of calcium phosphate crystals.

These crystals increase in size in the presence of supersaturated phosphate and calcium ions in the renal system, forming kidney stones. Calcium phosphate stones usually grow larger than calcium oxalate stones.

Preventing Kidney Problems While Taking Smoothies

Preventing kidney stones is of paramount importance, especially for people susceptible to this problem. For instance, caution is advised for those taking smoothies despite a family history of kidney stones. Take the steps below to minimize your risk of developing kidney stones, whether you have a family history of this disease or not.

1. Make a kidney-friendly smoothie

You can include fruits with relatively low potassium, such as strawberries and blueberries, to make a nutritionally balanced smoothie. You might also consider adding a smaller portion of fruits or vegetables rich in oxalates, potassium, or phosphorous. For instance, you should avoid adding too much spinach to your smoothie owing to its high oxalate levels. Spinach contains more oxalate than most common sources, which makes it bad for your kidneys.

Reducing the amount of dairy products used to make a smoothie can also help limit potassium intake. In addition, mixing your smoothie with celery juice can benefit you because celery promotes kidney health and prevents the formation of kidney stones.

Substituting potassium-rich ingredients such as bananas with horned melon and other less nutritionally dense fruits might also help. Some low-potassium fruits you may add to your smoothie to make it more kidney-friendly include blueberries, apples, cranberries, and blackberries.

2. Take adequate levels of calcium 

You can also reduce your risk of developing kidney stones while taking smoothies by increasing your calcium intake. Including sufficient calcium in your daily diet helps eliminate most of the phosphate and oxalate in your intestines. As a result, only a small amount of these minerals will reach the kidneys for eventual removal.

You should take calcium-rich foods or a calcium citrate supplement with high oxalate smoothies to reduce your susceptibility to kidney stones. The former is obviously better. However, if you choose to take calcium citrate supplements, you should avoid those containing vitamin D because vitamin D may encourage the formation of calcium oxalate stones. Most calcium citrate supplements have vitamin D except for a few.

3. Reduce salt intake

As noted, limiting sodium or salt intake can minimize your risk of developing kidney problems. Generally, having a high concentration of sodium prompts the body to excrete this mineral. As the body removes the excess sodium, it concurrently expels a significant proportion of calcium, creating the right conditions for kidney stone formation.

Reducing salt intake decreases the need to excrete excess sodium along with the calcium in the body. On this note, you should restrict your daily salt intake to about 2-3 grams. Cutting your consumption of processed foods, such as fast foods, might help decrease your salt intake.

4. Drink enough fluids

Taking at least two liters of water can help prevent kidney stone formation for those taking smoothies containing high levels of oxalate or phosphate. Sufficient fluid intake ensures urine does not become highly saturated with these substances, preventing the development of calcium phosphate or oxalate crystals in your kidneys.

5. Take smoothies in moderation

Too much of anything can have unintended consequences. The same applies to smoothies, with the green ones posing a more significant problem. For instance, consuming excessive oxalate-rich green smoothies can increase your risk of kidney problems. Therefore, exercise caution with these beverages and only take a small amount everyday as part of your weight loss diet or for other health benefits.

6. Rotate your ingredients

You should also consider rotating your smoothie ingredients to ensure you do not exclusively take fruits or vegetables containing high amounts of substances that encourage kidney stone formation. This move enables you to control your daily nutrient intake in the smoothie, keeping your kidneys healthy.

7. Limit your vitamin C intake

You should further not take larger doses of vitamin C because its metabolism leads to the development of oxalate as an end product. This oxalate, coupled with the one taken in a smoothie, can combine with calcium in the kidneys, leading to calcium oxalate stones. On this note, you should not concomitantly take oxalate-rich smoothies and vitamin C supplements in doses exceeding 500 mg.


Smoothies may be bad for your kidneys. The green smoothies pose a most significant risk to your kidney health because leafy vegetables often have high oxalate levels. This means that they can expose you to kidney stones. Some other ingredients added to smoothies may also contain high potassium and phosphorous levels. These minerals can harm kidneys if taken in high amounts. However, following the steps above can help you make kidney-friendly smoothies.

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