Thanks, Rian. I read that explanation when I was researching, and it might hold true, but in my case the pain vanished within 24 hours of eating. Given that, the ‘fast abdominal fat-loss’ issue doesn’t make sense. My fat loss held, within 24 hours of breaking the fast, but the pain evaporated.
I read in Valter Longo’s book, in a discussion about the pros and cons of Prolon, his fasting mimetic, that one con could be ‘lower back pain’. I messaged his FB page asking what would cause such pain but didn’t get an answer.
I’m thinking of going to True North I’m March to do a true extended fast. It’s clear to me now that without extreme circumstance (straight jacket, desert island, ‘fasting facility) I’m not likely to fast for a long period. And while the short fast helped my inexplicable belly distention, it didn’t fix my constipation, which is my #1 reason for fasting.
True North aligns with the vegan religion, so could be bumpy on the refeed. But then again, my high fat/low carb lifestyle was in full swing when my health went whacko, so 3 days of fruit and veg refeed might be a good change of pace. I wonder how I’ll look at fruit after a long fast? Probably love it versus my current DANGER view 
Let me know how your back did with the golf swing and breaking the fast. Thanks again for sharing your info.