I am a 60 year old lifelong cyclist, ectomorphic build. I have fasted for 24 hours (dinner time to next day's dinnertime) once weekly for about 5 years now. When fasting, I incorporate moderate exercise throughout the day, usually periodic sets of pushups and pullups, sometimes a 30 or 45 minute ride.
I can report I have no problem maintaining muscle or body mass with this regimen.
Further I can recall a few minor hangry episodes while fasting, early on. But like fasting itself, it became progressively easier for me to fast over time.
