Oats, like all grains, nuts, seeds, legumes, and tubers, contain phytate (also called phytic acid). Phytate is an anti-nutrient and blocks absorption of minerals, especially iron, calcium, zinc, and manganese. The effects of this can be seen in the archeological record. It took mankind about 2500 years to change from hunter-gatherers to farmers across the planet, and as humans started eating grains, the bones and teeth of our ancestors started showing signs of malnutrition and new diseases. Phytase is an enzyme that helps break down phytate. It should be noted that the anti-nutrient effect of phytate only lasts for the duration of that meal. However there are ways to reduce phytate and increase phytase in foods. Sprouts are low in phytate. Another way is by germination or malting. Another way is by fermentation. And another way is by soaking.
Here's a good scientific abstract on the topic …
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6261201/
Oats are particularly high in phytate and contain no phytase, so they should be soaked for a minimum of 12 hours, and ideally for 24 hours. Here is the way I do it. Place 2 litres of uncooked dry oats in a big pot. Mix in 8 TBSP of buckwheat ... buckwheat is not actually a grain, but rather a fruit, and contains a lot of phytase. Fill with warm water ... the warm water will start a slight fermentaion process ... add enough water to cover the oats by at least an inch. Add 8 TBSP of apple cider vinegar ... this will provide the acid to draw out the phytate. Cover and leave on the counter at room temperature for 24 hours. After 24 hours rinse thoroughly in cold water. Add 8 TBSP of buckwheat again ... I add this step because the rinsing process removes most of the buckwheat I think and I don't know whether the phytase was absorbed into the oats or is just washed away in the rinsing, so this insures that my cooked oats will contain phytase. Then add about the same amount of water as was used to soak (depending on desired consistency) and cook until the excess water is gone. Then store in the fridge in a covered container ... I use a large protein powder container. You'll now have a few days supply of oatmeal. Note that once cooled in the fridge, the consistency will be much firmer than when it was hot.
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