What I did for my fiancé was to educate him on fasting. Watch a documentary, read parts of study while hang out and explaining the benefits. After he got comfortable with the idea of fasting I invited him to join me on a fast as a couples challenge. We did a five day fast, he enjoyed it and now continues to IF most days for health benefits not weight loss. Maybe ask him to join you for 24 or 48 hours and discuss it frequently
It sounds like you two need to be communicating. You’re afraid to tell him that you’re fasting. He should be on your side and supporting you.
Edit to add: Also, sorry, I didn’t give you any ideas for broaching the subject. In my experience, being straightforward and calm is the bes avenue. “Hey I’m thinking about doing multiday fasts. Here are some risks…and here’s how to mitigate…”
I totally understand. My husband doesn’t like the idea of extended fasts, and even gets super concerned if he thinks I haven’t gotten enough calories in each day.
Slow gentle education is what I’m trying. He’s on board with keto, which is huge! So we’re definitely getting there. But slowly. So. Slowly. Haha
Edit: just adding that I only do extended fasts when he’s out of town. So…. about 2-3 days is my longest.