At least if you follow a certain sub set of “health gurus”… they are.

According to “The Healthy Home Economist“, Green Smoothies can “devastate your health”.

Why? How you ask? According to this blogger’s post on the subject (though the view isn’t solely hers)

“Frequent consumption of large quantities of raw, leafy green vegetables as occurs when a person drinks green smoothies can be deceiving at first as a person will probably initially feel great after adopting this habit particularly if he or she is coming off a highly processed, nutrient poor diet.

The vegetables used in green smoothies are almost without exception high oxalate foods. Over time, a high oxalate diet can contribute to some very serious health problems particularly if you are one of the 20% of people (1 in 5) that have a genetic tendency to produce oxalates or if you suffer from candida or other fungal challenge. In those cases, a high oxalate diet can deal a devastating blow to health.”

Criticism of Green Smoothies, and particular, warnings over Oxalic Acid go even more broad than that.

A doctor called Caldwin Esseltyn drew controversy for the video below where he stated bluntly:

“Avoid smoothies. The fiber is so finely pureed that its helpful properties are destroyed. The sugar is stripped from the fruit, bypasses salivary digestion and results in a surge of glucose and the accompanying fructose contributes to inflammation and hypertension.”

(A more balanced breakdown of Dr. Esseltyn’s comments can be seen at

So what the heck is all this about?

Do You Really Need To Quit Drinking Green Smoothies? Is Spinach Going To Give You Kidney Stones?

Here at we dislike a few things:

1. We dislike anecdotes about people’s health (I drank green smoothies for two months and I felt a pain in my abdomen!)

2. We dislike pseudoscience (Or the taking of real research and using it to justify unrelated premises)

3. We dislike “opinions” when it comes to health.

And sadly it appears that all 3 are at work in the case of the “devastating Green Smoothie”

Oxalic Acid What?

Turns out, like many things in the health arena, not a whole lot is known about Oxalic Acid.

I mean, we know a little bit. This PDF I found by the Children’s Medical Center of Dayton (of all places!) describes a lot of the existing research.

For example, we know reasonably well (but not perfectly) how much Oxalic Acid is in certain foods.

For example, Spinach has the highest Oxalate level of any food measured (kicking off the Green Smoothie Controversy) at 645mg/100g.

Fibre One Cereal is pretty high too, at 142mg/100g. And Bran Flakes are up there: 141mg/100g

What else?

Well, according to the same PDF,

“Evidence is now emerging that the absorption of dietary oxalate makes a major contribution to urinary oxalate excretion, particularly in stone formers.” where “Stone Formers” are the “1 in every 1000 adults hospitalized annually with Kidney Stones”.

So just to be clear, there IS evidence that dietary oxalate from spinach in your green smoothies is a major contributor to urinary oxalate excretion, more so if you already have kidney stones.

But check this next sentence, to get a sense of how complex this issue really is…

“The factors that influence this absorption are known to include the oxalate content of the foods eaten, the concentrations of ions in these foods that bind to oxalate and limit its absorption such as calcium and magnesium, the presence of bacteria that can degrade oxalate, the transit time of food through the intestinal tract, the inheritance of certain genes, and quite possibly several other as yet unidentified factors”.

Translation: “SO MUCH other stuff could be going on”.

Take Note Of What’s NOT Said

Notice you don’t hear any discussion in any of the mentioned articles, that might answer questions like…

Q: How much Spinach would you have to eat to over elevate your Oxalic Acid levels and make it dangerous?

A: There is no clear evidence on the matter, so no one has any idea.

Q: What is even IS a high Oxalic Acid level? Like at what level could it give you kidney stones?

A: Even on THAT there is no credible evidence, so no one has any idea.

However, for your interest, the Wikipedia entry tells me that the New England Journal of Medicine

“reported acute oxalate nephropathy “almost certainly due to excessive consumption of iced tea” in a 56-year-old man, who drank “sixteen 8-oz glasses of iced tea daily”. The authors of the paper hypothesized that acute oxalate nephropathy is an underdiagnosed cause of kidney failure and suggested thorough examination patient dietary history in cases of unexplained kidney failure without proteinuria (an excess of protein in the urine) and with large amounts of calcium oxalate in urine sediment.”

8 x 16 ounces of iced tea every day. HBS recommendation: Don’t do THAT!


If you have kidney stones, or a family history of kidney stones, kidney doctors will caution you about packing a blender full of spinach leaves and press go EVERY single day.

If you’re everyone else, and you throw some spinach into a smoothie of fruit and vegetables each day, it’s highly unlikely that Oxalic Acid is going to cause you so much as a lost eyelash.

Stay healthy my friends. But stay smart!