They don't. When I created a fitbit account, I chose whether or not I wanted my profile public. Then, when I want to log an activity, I enter in a name and dura

They don't. When I created a fitbit account, I chose whether or not I wanted my profile public. Then, when I want to log an activity, I enter in a name and duration for it. So if I choose to have a public profile, accessible to the world (which was clear to me when I signed up), then I choose to make an activity called "sexual activity", it's indexable and publicly visible.