wolf116 said:
I do grind them myself. What makes the oil oxidise? Heat? Air? Maybe the grinding process would create too much heat.
I've heard people say to soak them in water for 24 hours prior, then add it to your shakes.
You just need air, but heat will speed up the process. The polyunsaturates in fish oil are similarly unstable, that's why bottles of quality oil are flushed with nitrogen, refrigerated and have antioxidants like vitamin E and rosemary extract added. I doubt that many brands of flax oil go to the same measures to prevent rancidity.
I'd think that the oxidation caused by grinding would be minimal and not enough to worry about, you just need to avoid the oils and pre-ground seeds that sit on the shelf at ambient temperature for who knows how long having been processed using who knows what industrial methods.
From wikipedia:
"Flax seeds are chemically stable while whole, and milled flaxseed can be stored at least 4 months at room temperature with minimal or no changes in taste, smell, or chemical markers of rancidity.[4] Ground flaxseed can go rancid at room temperature in as little as one week.[5] Refrigeration and storage in sealed containers will keep ground flax from becoming rancid for even longer."
Soaking is most likely used to decrease the anti-nutrients such as digestive enzyme inhibitors that are present in most seeds and nuts. That's fine, but the whole seed is still indigestible and will just pass straight through you, so you still need to grind them.