This app seems completely broken to me.
I've connected it to MyFitnessPal and I've enabled everything in the settings, but here's what I've noticed:
1. It only displays new data, not anything from the past. So it will only gather new entries I've made into MFP, not previous data I've inputted.
2. Even there, it often messes up. Some data seems to go in while a lot doesn't. For example, I entered my lunch and dinner calories into MFP yesterday, but only the lunch calories were shown in Health.
3. Today, the app seems to have stopped working altogether. I woke up this morning and saw that all the data is cleared. It doesn't have anything I've previously entered. Plus, even the graphs I've added to the dashboard are gone. I try to re-add them, and they simply won't add. My dashboard is empty and I can't seem to change that.
4. The design of the app just isn't very good. It's hard to read, you can't customize anything besides the time period, and you can't even go in and examine each day's calories or steps or whatever. The 'show all data' breaks it down almost to the second, but you can't see your daily results. Also, it would have been nice for more customization and perhaps, a landscape mode. But first they need to fix the thing so it's actually usable.
tl;dr - Health is quite possibly the most unfinished and downright half-assed app Apple has ever released.