I've been IFing for the last 3 months and have made more progress reducing body fat then ever in my life... Including some drastic cutting periods where I'd consume pre-portioned meals, like clockwork, every 2-3 hours.
I've also managed to keep my scale weight relatively stable the entire time, implying a gain (visually, it goes beyond "implying") of lean tissue.
I typically fast from 10pm every day, and through most of the work-day until 2:30pm. At this time I have a whey protein shake or a serving of BCAA's (since I'm fairly intolerant to whey protein) or some lactose-free milk. I consume a 500Kcal (60g protein, 35g carbs, 10g healthy fats) meal of lean protein and complex carbs around 3:30pm (typically consists of a tuna/mackerel melt sandwich in hemp/flax bread), which allows some digestion time before my 6pm workout. After working out I'll consume my other daily 1500Kcal of high protein, lean foods. I absolutely cannot train in a "fasted" state (nor do I think this is advocated), but I do spend most of my active waking hours fasted. Once a week I break fast and consume 3000Kcal, usually on my heavy squat or deadlift day, to keep my long-term metabolism up.
Though I do have hunger pangs, I'm more alert and focused during the waking hours. I usually engage in at least 45m light cardio (uphill walking at lunch time) during the fasted period.