The Low Down on Oats and Phytic Acid

If you eat grains and follow an ancestral diet, you’ll probably have heard that we should soak our grains (or flour) in water and an acidic medium before cooking. This process not only softens and hydrates the grain, but it also helps neutralise ‘anti-nutrients’ that can bind to minerals and therefore stop you absorbing them.

Phytic acid is perhaps the most well-known of these mineral-stealing ‘anti-nutrients’. It’s possible to neutralise the damage that phytic acid potentially does by activating another compound that is naturally-present in grains: phytase. Phytase is an enzyme in grains which breaks down the chemical structure of phytic acid and stops it doing its potentially damaging work.

Hence one of the tenets of ancestral cooking: soak your grains. This action helps activate phytase allowing it to break down phytic acid, meaning you don’t have to worry about not absorbing the minerals in your meal.

What’s different about oats?

This logic, although sound for most grains, doesn’t extend to oats for two reasons:

  1. Oats are naturally low in phytase.
  2. Virtually all oats are processed in a kiln before they get to us. This action most likely destroys phytase.

So, soaking oats in water and an acidic medium doesn’t help when it comes to inactivating phytic acid; there’s no phytase in the oats to act as a catalyst. Soaking oats like this will soften and, if you use an active starter, predigest some of the complex carbohydrate, but it will not solve the phytic acid problem.

The standard answer

The standard answer to this dilemma is to add in a grain that is high in phytase (like rye) to your soaking medium. I have followed this advice for years, using my wholegrain rye sourdough starter when I soak my oats.

And I would have continued this way, had I not delved deeply into oat and grain science for the book on oats I’m currently researching. The piecing together of information from many scientific papers has led me to understand that the method (of adding rye sourdough starter) that I’ve been using for over a decade is no good either.

Here’s why:

As soon as grains are ground into flour, the enzymes in them are exposed to oxygen and start to degrade. This includes phytase. So, if you’re using anything other than a high phytase grain that’s been freshly-ground, it’s probable that there’s no phytase in your flour.

In order to do our best to potentially inactivate the mineral-stealing phytic acid we need to include a high phytase flour such as rye (or buckwheat) with our soaking oats AND that flour needs to be freshly-ground.


Learning this information is part of the reason why I now have a Mockmill electric grain grinder on my kitchen counter. I freshly-grind a handful of rye berries every time I soak oats for my morning oatmeal.

If you’d like to know how I do it, check out this post; The Best Way to Soak Oats.

If you want to hear more about this topic, you can listen to Ancestral Kitchen Podcast #70 – Fermenting Oats

The last word: As far as I can see, no-one has done a direct study on this – actually setting a scenario with freshly-ground flour and then measuring subsequent phytase levels, but the conclusions are clearly deducible from information in grain studies. (If you want to have a look yourself, read the words and quoted studies on the comments of this post (many thanks to Richard!))

7 Responses

  • Do I need to soak my oats overnight and rinse them The next morning to eliminate or reduce phytates?

  • When you say a handful, about how much rye do you mean? With how much oat? Steel cut, whole oats or rolled?
    Can buckwheat groans (unroasted) be used instead. This grinds in a blender, whereas rye does not.
    How finely does the rye or buckwheat need to be ground? How long and st what temp soak? I can’t usually manage 65 degrees, but 68 winter and 75 summer works.
    Would millet work? Quinoa? High enough in phytase? Taste better with oats in my opinion. Does taking certain strains of probiotics help? Cooking the oats with dried fruit/ apples, prunes, cranberries, figs?

    • The quantities I use are in this post:

      I use rolled oats.

      Yes, you can use buckwheat. I would grind as finely as possible (as long as you can do this without overheating it).

      I would soak overnight and warm, if you can. The more you can create a good environment for phytase, the better.

      I wouldn’t use millet or quinoa. They don’t have enough phytase.

      I have not come across any studies showing probiotics help and dried fruit doesn’t contain phytase, so wouldn’t help with this particular issue.

    • I would feel happier eating sprouted oats regularly than unsoaked, unsprouted oats. I like what the sprouting process enables. However, I don’t think there’s been much conclusive research on sprouting oats and phytic acid. I’ve read one source saying it didn’t help, others saying it does help.

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