Probably more than you realise—and maybe not the message you’d like to be heard.
There’s nothing new about this, of course: We’ve been aware of non-verbal communication for a long time.
But we’re inclined to forget just how a potent a medium it is—and generally one that doesn’t lie. (As John Grinder said, “Treat all conversation as unsubstantiated rumour unless backed up by congruent non-verbal behaviour.”)
So it’s very difficult to fake non-verbal communication: To communicate interest non-verbally when actually you’re bored, for example.
In fact, really the only way to communicate interest is to be interested—if not in the actual content, then perhaps how the person manages to be so consistently boring, if that’s what they are, or some other aspect of what’s going on.
And the only way to communicate support is to be supportive, even if you’re not in actual agreement.
In other words, you need to manage your internal state if you want to control your external signals.
Or, you could find a way to verbalise appropriately what you’re actually feeling, even if it is a difficult message. That’s quite possibly what’s being understood anyway. At least then you’d be regarded as authentic and real. And that might have benefits.
Worth reviewing your silent communication—and indeed that which you “hear” from others. You might notice how loud some of the signals are.