Dealing with concerned family members?

Hey so whenever I fast for longer than 24 hours my family will notice and they've gotten moderately concerned about it. I have a hard time explaining it to them. While I've been able to do 60-90 hour fasts my biggest struggle with trying to do longer is having others be concerned. If I be honest with them and give any explanation it doesn't help so I've had to resort to lying if others ask me. Any recommendations of how do explain this and to prevent concern?