Green smoothies have become the poster child for health enthusiasts everywhere.
Made with leafy greens like spinach and kale, plus apples or bananas for taste and extra nutrients, they seem like an obvious health food. In fact, some medical doctors have praised them as a great source of B vitamins and for supporting a healthy nervous system.
But not everyone agrees.
Entrepreneur and author Dave Asprey (@dave.asprey), known for his Bulletproof brand, is sounding the alarm.
In an Instagram clip that has racked up over 1.2 million views, he warns that green smoothies might not be as healthy as they seem.
What’s wrong with green smoothies?
“There are people who have gone to the hospital and died after 10-day green smoothie cleanses,” he claims in the clip.
Asprey alleges that some of the worst offenders are spinach, kale, beets, almonds, raspberries, and even chocolate. He blames them for contributing to kidney stones, which, according to him, aren’t caused by meat or beer, but by plants.
“Seventy percent of kidney stones are caused by plants, not by eating meats, not by drinking beer,” he said.
The reason, according to Asprey, is oxalates—naturally occurring compounds in many plant-based foods.
“When you eat foods high in oxalate, they form razor-sharp microscopic calcium crystals,” he explained. “They cause kidney stones. They cause damage to the urethra, and anywhere you’ve had an injury, they go there first and then it starts to hurt.”
According to Asprey, this could explain unexplained aches and pains people experience after eating certain foods.
“You eat a meal high in oxalate… you wake up the next morning and you’ve got like muscle tension, your back hurts, your knees are stiff,” he said. “That one place where you sprained your wrist or something, it hurts.”
Asprey also claimed that the body can only excrete 200 mg of oxalates per day, yet one green smoothie can contain up to 1.5 grams.
“The beginning lethal dose of oxalate is 5 grams,” he said.
What do experts say?
While high-oxalate foods, such as spinach and beets, can contribute to kidney stones for some people, Asprey’s claims go much further than standard medical advice.
It’s important to note that some of the foods Asprey listed as high in oxalates, such as kale, raspberries, or chocolate, are actually considered low to moderate in oxalate content.
The National Kidney Foundation, for example, acknowledges the link between oxalates and kidney stones, but they don’t recommend avoiding high-oxalate foods entirely.
Instead, they suggest drinking plenty of water and eating calcium-rich foods alongside them to reduce oxalate absorption.
Studies show that while excessive oxalate intake can lead to health issues, it would take an extreme amount—far beyond a typical diet—to reach toxicity levels.
The tragic case Asprey mentioned—of a woman who died after a 10-day green smoothie cleanse—involved additional risk factors. She had undergone gastric bypass surgery and was on antibiotics, both of which can increase how much oxalate the body absorbs from foods like spinach.
It’s also worth noting that the body can actually excrete up to 250 mg of oxalates per day.
According to NutritionFacts, reaching the point where any excess oxalates remain in the body would require eating more than “25 cups of collard greens, 60 cups of mustard greens, 125 cups of kale, or 250 cups of bok choy at a time.”
They advise consuming high-oxalate foods, especially spinach, in moderation.
As for the idea that oxalates trigger pain in past injuries, there’s little scientific evidence to support it, and it mostly occurs in patients with preexisting conditions.
At the end of the day, moderation is key. If you’re worried about oxalates, it’s a good idea to talk to a doctor before ditching entire food groups.
Commenters react
In the comments, some users agreed with Asprey and shared their own negative experiences with oxalate. Others, however, criticized the claims as unsubstantiated.
“Yes!! I’ve had kidney stones 3 times ! Oxalates!!,” exclaimed one user. “Lithotripsy twice 8 yrs ago, again end of 2024 Green vegetables, potatoes, chocolate, etc… painful!!!”
“Nice, but why doesn’t he present any scientific data, facts?” asked another critically.
“This is misinformation,” wrote a third. “all things in moderation plenty of fluids …for kidneys.”
The Daily Dot has reached out to Dave Asprey via email for official comment.
