Flaxseeds contain heart-healthy polyunsaturated fatty acids (PUFAs) including omega-3 fatty acids and conjugated linoleic acid (CLA).
Pre-ground ones are exposed to oxygen longer, which causes the PUFAs to breakdown and become rancid ₍₍ (̨̡ ‾᷄ᗣ‾᷅ )̧̢ ₎₎. You can detect this by its off smell/flavour.
So the best way is to buy whole flaxseeds and grind only what you need with a coffee grinder. It's probably cheaper to buy whole flaxseeds than packages pre-ground ones. Remember, wholesome is awesome! HappyHumpDay everyone ◡̈⃝!