I'm not a "leangains" or big on IFing, so take it for what it's worth. I'm all about "accidental IF" meaning you go along grok dumb and happy, poof don't feel the need to eat so you don't, which ends up being an 18-24hr fast. I'm not a fan of trying to force yourself into a fast.
Last week I had an accidental IF until about 7pm, I work out around 6pm. I ended up squatting 15 lbs more than before. I usually only see 5-10lbs gains, so it was at least an extra 5 pounds. Also feel really good that day.
That being said, training while fasting is fine, but personally I wouldn't recommend doing it all the time or more importantly trying to force your body into it. YMMV
"Go For Broke"
Fat Kine-230/24% @ 6'2"