Right now I have 25g carbs meal one then take my synthetine maybe 30 mins later. Then I train with 25g carbs intra. I was doing 2iu slin with that but dropped it after 50 days.
On cardio only days I either have 16g fat or its done fasted then sip on bcaa during cardio.
Both those scenerios have been working well for me.
If you don't want carbs or to use slin and wanted to drop bodyfat I would still use it. I imagine it would just take longer to build up in your system. Like Elvia said Leucine will help create an insulin spike as well, just not as big of one.