Doesn't decaf also contain caffeine, just a lot less of it?

Typical extraction yield is 18-20%. For a 20g dose that's 4g of material consumed, or about 30 individual beans.

I wonder if you could find similar effects with 4g or broccoli sprouts, or garlic, or ginger, or cumin seed, shiitake mushroom, seaweed, soursop leaf, or...