Green smoothies

Oxalates in green smoothies and salads – devastating to health?

In Diet, Nutrition and Recipes, Health and Nutrition by Dr Casey ConroyLeave a Comment

Maybe you’ve been scared to include green smoothies in your lunch of late? An anti-green smoothie blog may have turned you away from trying or consuming salads, green smoothies and/or juices on a regular basis. Read Casey’s balanced suggestions and you can keep eating the healthy foods your body needs.


Concerned readers may have heard about or read an anti-green smoothie blog that caused sensation in the not-so distant past that was titled, “How Green Smoothies Can Devastate Your Health”. The author argued that green smoothies could raise oxalate levels in people with oxalate toxicity, which could have devastating effects on health ranging from fibromyalgia and kidney stones to oxalate stone formation in the brain.

The oxalate issue has been one that has scared many people away from trying or consuming salads, green smoothies and/or juices on a regular basis, which I feel is a shame because it can keep people from eating the healthy foods their bodies need.

What are oxalates?

Oxalates are organic acids that occur naturally in humans, animals, and plants. They are made naturally in the human body. Similarly, our bodies convert many of the things we consume (like vitamin C) into oxalates. When combined with potassium and sodium, oxalate forms soluble salts. When combined with calcium, however, oxalate produces calcium oxalate, which can form kidney and other types of stones. This occurs because calcium oxalate is relatively insoluble; so it combines and hardens instead of harmlessly excreting as a waste product.

Where are oxalates found?

Some foods, such as spinach and beetroot greens, contain higher levels of oxalates than others. If your body absorbs high levels of oxalates and does not process it well, it may result in the formation of calcium oxalate stones, which most commonly form as kidney stones. Some people are more predisposed to this condition than others. However, no clear evidence exists linking dietary oxalate restriction to formation of fewer calcium oxalate kidney stones.

Other foods that increase oxalate levels in the body more than others include rhubarb, soy, beetroot, chocolate, wheat bran and tea.

Raw vegetableOxalate content in milligrams per 100 gram serving
Beetroot greens610
Collard greens74

(Table adapted from the following sources: (1) United States Department of Agriculture, Human Nutrition Information Service, Agriculture Handbook Number 8-11, “Composition of Foods: Vegetables and Vegetable Products”. Revised August 1984; (2) data gathered by LithoLink Corporation, a metabolic testing and disease management service for kidney stone patients, founded by Dr. Fredric Coe, a University of Chicago Medical School Professor, and posted on its website at; (3) data presented by Holmes RP and Kennedy M. (2000). Estimation of the oxalate content of foods and daily oxalate intake. Kidney International(4):1662.)

When to restrict oxalates

Some conditions require oxalate restriction (50 mg per day or fewer), but these conditions are rare. Conditions affected by oxalates are:

Primary and enteric hyperoxaluria: A genetic predisposition to this disorder occurs in less than 1 percent of the population.

Hypercalciuria type II: A form of excessive urinary calcium excretion that exists in less than 10 percent of the population.

Dietary hyperoxaluria: Arising from dietary factors, this more common condition is associated with the formation of calcium oxalate kidney stones. In cases where patients develop calcium oxalate kidney stones, physicians do recommend moderating intake of high oxalate foods such as animal protein. Kidney stones occur in about 10 percent of the population.

In my professional experience 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. It is widely recommended to reduce animal protein in relation to kidney stones, over green leafy vegetables. High levels of animal protein may be a significantly larger contributing factor to this condition than vegetables, as the kidneys have to filter out the by-products of animal protein digestion and metabolism.

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 cause to give up your wonderful green smoothies and juices – you just need to be aware.

Many plants are toxic for various reasons when consumed in excessive quantities as a defence against being eaten by pests and predatory herbivores. So, although I love kale, I make sure I rotate the types of greens used from day to day. Spinach is the main one to be aware of if you’re watching your oxalate intake. 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, bok choy, watercress, cabbages, sunflower sprouts and alfalfa sprouts.

During my veterinary years, I noticed that grazing animals eat large quantities of greens, but they tend to eat a variety of different greens so they do not auto-intoxicate on oxalates or any of the other compounds found in the greens.

Minimising the effects of oxalates

If you’re still concerned, here’s how you can minimise the potential effects of oxalates:

  • Eat plenty of dietary calcium from plant-based sources. Some evidence exists to suggest you can mitigate the effects of oxalates by drinking fluids and consuming more dietary calcium.
  • Rotate your greens. Switch your salads and smoothies so you are consuming a variety of greens and other non-starchy vegetables.
  • Minimise juicing if you have formed calcium oxalate kidney stones in the past or are concerned about oxalate. Juicing may be more problematic because you are removing parts of the whole food (including fibre), thus increasing concentrations of other substances. A smoothie, however, contains every part of the whole food, which may minimise oxalate problems.

Intuitive greening

If you’re a green smoothie lover and have been stung by the oxalate scare, I hope this helps you to make an informed decision about your health.

While oxalates may cause a problem in a small percentage of the population, it would be a shame to allow fear of a condition that occurs in an unlucky few to keep you from realising the tremendous benefits associated with consumption of raw, leafy greens. Brimming with vitamins, minerals, fibre, antioxidants and enzymes that have such a positive effect on your health, the benefits of green leafy vegetables far outweigh the risk of developing a condition that affects such a small portion of the population, especially if you vary your greens.

In the end you are the highest authority on your own body. Be aware of how you feel when you drink green smoothies, and 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.

About the Author
Dr Casey Conroy

Dr Casey Conroy

Dr Casey Conroy, MNutrDiet, BVSc, is a holistic dietitian and nutritionist, naturopath in training and yoga teacher who specialises in women's health, hormones, and the Health At Every Size approach to weight and body concern. She is the founder of Funky Forest Health & Wellbeing on the Gold Coast, and she loves chocolate and any yoga involving an eye pillow..

Share this post

Leave a Comment