Your Flex will sync with your Fitbit dashboard and your Fitbit dashboard can sync data between it and MFP is you allow it. Fitbit "adjustments" will be pushed to MFP and calories, meal "summaries", and exercises can be synced from MFP if you desire. Do you have a specific question?
Best AnswerWhen the apps are connected, they feed each other information on what you have logged. For example, I log all of my food in MFP. A summary of that information gets pushed to my Fitbit account and is used to calculate calories in versus calories out. The info also appears in my food log here.
I log all activity here and the calories burned get sent to MFP.
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