It's easy to connect to and sync with Google Fit on Android.
To start, navigate to Settings in your main (left) navigation menu.
On the Settings tab, scroll down to the Carb Manager App Settings section, then the Fitness Device Links subsection. Toggle Connect with Google Fit to On.
Carb Manager should then begin syncing with Google Fit.
Important: These settings do not appear on the web version of the app. You must follow this step directly from your mobile device.