I have been an IF'er for 4 or 5 years, always work-out | ride, run, swim, weights | in a fasted state. The issue for me was to develop what is commonly referred to as a metabolic flexibility, and I have always suffered wild insulin spikes ingesting sugar and carbs during the day. I can pack on fat just by smelling a loaf of bread.

After a long run I'll use a protein shake for recovery, but that's when it seems necessary.

It works for me, but generalizations about fasting are difficult to support. I doubt many people would be comfortable running 3 miles before work, then putting in a full day without food until 5:30pm. Additionally, I don't consider it a viable competitive athlete diet. Endurance efforts, maybe; IF'ing seems to have become a fad in the endurance running game, as is high fat diets.