I have tried it several times and, to be honest, have struggled each time. My issue was not the low kcal days (which I found quite easy) but the days around it, where I tended to overcompensate and binge. At best, I broke even each week with bodyweight static. Which isn't ideal when trying to shed fat, not to mention the negative feelings associated with overeating and being unable to improve body comp despite a shed-load of training. I do think the latter is related to whether this diet works. I was doing minimum 5 days a week, sometimes 6, which usually meant training on the fast days. Now if I can do one or two low kcal days a week I will, but daily totals may be closer to 1000-1200 rather than the 600-800 prescribed.