It may be that myristicin(the active compound in nutmeg) breaks down during cooking. Additionally myristicin is not very well absorbed, and the fact that it's mixed into food would likely reduce its absorption significantly.
Also, I just want to mention that tripping on nutmeg is not something I'd recommend to anyone. It may not kill you outright, but it will make you delirious enough that you're no longer aware of your surroundings, what you're doing, and you may end up harming or even killing yourself. It's a deliriant, not a psychedelic. You're also likely to get intense muscle aches that will make it thoroughly unenjoyable even in sub-hallucinogenic doses.
i know someone who has tried it. you need a large amount of raw, powdered nutmeg, like 1-2g per kg of bodyweight, and that much is hard to get down.
then you don't really trip, you just kinda hallucinate, something closer to extreme sleep deprivation hallucinations than talking to Lucy in the Sky with Diamonds.
Also, I just want to mention that tripping on nutmeg is not something I'd recommend to anyone. It may not kill you outright, but it will make you delirious enough that you're no longer aware of your surroundings, what you're doing, and you may end up harming or even killing yourself. It's a deliriant, not a psychedelic. You're also likely to get intense muscle aches that will make it thoroughly unenjoyable even in sub-hallucinogenic doses.