Nxd5 in the Grunfeld, sound, playable or just bad?

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Avatar of congrandolor

I was playing this mail game, so I decided to play 1.d4 (I play 1.e4 almost 100% in blitz). My opponent chose the Grunfeld. Then, on move five, I got distracted, and instead the standard e4 automatically played Nxd5. Is it bad? Do white lose material or something? Why is never played at master level?

By the way, I won the game, but after suffering quite much