Question: I’ve heard that eating too many greens is bad for my kidneys. Is that true?

Answer: While eating cooked greens, or even eating plenty of raw greens in salads, is fine, it is possible to get into trouble if you drink large amounts of raw greens in daily juices or smoothies. But rest assured—if you like green smoothies, there are ways to enjoy them safely, even daily.

Some greens—spinach and beet greens in particular—are very high in oxalates, which can produce kidney stones. In rare cases, a very high oxalate diet can even produce kidney failure. In one medical case, an 81-year-old man who replaced all his meals with oxalate-rich green juices developed kidney failure.

It’s easy to avoid that fate if you follow a few commonsense tips. Unless you have been told to avoid oxalate-rich foods by your doctor, it’s fine to eat plenty of greens, even raw. Cooked greens are even better, since steaming or boiling greens removes some of the oxalates. Vitamin C, also in spinach, binds some oxalates in the gut so that they’re less absorbed. Foods rich in calcium also bind oxalates.

Even having a daily green drink can be done safely: Just limit yourself to no more than one 10-to-12-ounce serving a day. You may also want to use lower-oxalate greens such as kale…add in an additional 1,000 mg of powdered vitamin C…follow the green drink with a healthy meal…and consume plenty of water throughout the day. Your kidneys will thank you for it.

Do you have a question you’d like to ask our experts? Send us an e-mail at with “Ask Expert” in the subject line.