Meat Eater says:

R Commit: Before you pay a momentum cost, you count having already paid 1 momentum toward the cost.

*Ninon* says:

R: If you discard 1 or more of your momentum, discard one of your opponent's 1 momentum.

Question is, does using Meat Eater and NOT actually discarding any of your momentum count towards triggering Ninon's ability?

No, because you didn't actually discard anything from your momentum. Meat Eater basically just replaces what you would have had to discard.

Stamp for kilik850. If you meat eater, you didn't actually discard momentum, you just count as having discarded 1 toward that cost specifically.