The problem with walnuts is their 3 to 6 ratio. Flax seeds have 4:1 ratio while the walnuts have a 1:4.@steemitbaby
That's okay if you don't have any extra omega 6s in your diet. If you do, the short chain to long chain conversion will be not as eficient. You want to keep your ratios up to 1:4, ideal is 1:1.
Compared to any other omega 3 source, flax is the king in many ways.
Check out the video by Michael Greger on that: