A concerned, green smoothie-loving reader recently pointed out to me an article stating that: "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.... a high oxalate diet can deal a devastating blow to health."
Hear that? A DEVASTATING blow to health! (Insert bomb sound effect here).
The oxalate issue has been one that has scared many people away from trying or consuming green smoothies and juices on a regular basis, which I feel is a shame. I'm volunteering in India at the moment and would kill for a big green leafy salad, green smoothie or (the most impossible of all) a mixed veggie and green leafy juice - ohhh kill me now!!!
The paradox of scientific enquiry
In my professional opinion I have seen far more cases of kidney stones in people who consume excessive amounts of animal protein than people who drink a green juice or smoothie a day. That said, anything can be overdone - including using the same type of green in your green smoothies all the time! It is possible to overdose on spinach and experience symptoms of oxalate poisoning, but this isn't a reason to give up your wonderful green smoothies and veggie juices if you love those - you just need to be aware.
Many plants are toxic for various reasons when consumed in excessive quantitites as a defense against being annihilated by pests and predatory herbivores (a.k.a US!)
So although I love kale, I make sure I VARY or rotate the types of greens used from day to day. Spinach is the main one to be careful of if you're worried about oxalates. I will use kale one day, and the next use romaine lettuce, the next alfalfa sprouts.
Low oxalate greens you can use include lettuce of all varieties, mustard greens and alfalfa sprouts.
From my veterinary years, I noticed that grazing animals eat large quantities of green leafies, but they tend to eat a variety of different greens so they do not auto-intoxicate themselves on oxalates or any of the other compounds found in the greens.
In the end you are the highest authority on your own body, so whilst it's important to stay abreast of the latest research, also be aware of how you feel when you drink green smoothies for a while, how different greens and combinations work for you.
Know what your inner experience is as this "experiential evidence" is perhaps the most valuable, and individualised there is.
To your health! (And to varied, delicious and fresh green smoothies, salads and juices - enjoy one for me!)
Casey Conroy - Accredited Practising Dietitian, Accredited & Holistic Nutritionist