I've just come off of 6 months of BFL-by the book, free day included. I did a free day every week. I started calling it "Eating Disorder Day" because I would binge too much and feel very ill. I could eat 4000 calories in one day. I still saw good results with BFL (eating 1800 cals and 100% clean every day but Sunday). But, I did not meet my fat loss goals (due largely to out-of-control free days), so I'm now on CKD for my 3rd challenge. The free days can get way out of control for a lot of people, very easily. I also think it's one thing to eat high fat 6 days a week and have 1 high sugar day, I think it's much harder on your system to eat very low fat 6 days a week with one high fat day---I would think it would wreak havoc on the gallbladder. My advice on BFL free days: limit it to 1 free meal. Many people "got a handle" on free day by doing 2 free meals a week, any time during the week. HTH
Sue