I used to run regularly. I got to love it after a while, but I stopped when I developed an underactive thyroid - I just couldn't sustain exercise for long. That's when I started long-distance walking instead, and then hillwalking.
I used to run in 10km events, which really excited my competitive spirit. I also did a half marathon. My tip is to put on your favourite music on headphones when you run (turn it off when you cross the road!) A good tune can honestly make you run faster!
Re-intermittent fasting, I lost 31lbs on the 5:2 diet last year (2 x 500 calorie fast days a week). The headaches can be due to lack of salt - when fasting I always eat some sea salt and drink water.
500 calories a day is a tough achievement. I have lost weight in the past on a 1500 calorie per day target.
At the time I was playing regular Tennis and that made the difference. Ill take your tip about Salt and Water though, thanks.
Ah - 600 for men. And you can eat all you want the next day.