My mother is by far no healthy person, even though she many times think she is, but she's been a huge fan of Flaxseeds (Linfrön in Swedish) since I was a kid. She's never explained the great effects of Flaxseeds any deeper, more than "it's good for you", but she was right. Flaxseeds is the one of the greatest sources of Omega 3 (fatty acid), Omega 6 and are also great source of Potassium (regulates the body's fluid balance).
Ground Flaxseeds are easily and quicker absorbed in the body, so always chose ground Flaxseeds. The seeds have a hard shell and are small so they usually goes straight through the body if not grounded.
Another great effect of just a small dose as one or two tablespoons per day of Flaxseeds will help you burn fat. I make raw crackers out of Flaxseeds and they gives me a sense of fullness and keep me energized. I also use Flaxseeds to make raw pizza crusts and much more. They are also cheap, so no excuse not to buy a big bag today.