Some Google API requests will require a server security audit
support.google.com
support.google.com
Reading Google Fit data will require an external audit of the server involved and a fee of "between $15,000 and $75,000 (or more)" to a third party firm. This seems like a big barrier to reach a small market.
Is anyone else here currently using the Google Fit API? Will you continue to do so, and what size user-base do you have?
You may be able to avoid the external audit based on your use case