Hi! The 5+2 diet is an intermittent fasting diet. It involves eating only 500 calories a day on two days of the week, then eating "normally" (but sensibly) the rest of the week. Good ol' Wikipedia has a good description of it.
The advantages for me are (1) no "forbidden" foods; (2) it's easy to remember.
The major mod I've made to the 5+2 diet came from a book called "Man 2.0: Engineering the Alpha", which also has intermittent fasting, but done slightly differently. It's meant for men, but even so, I learned a great technique from it: Compressing your "eating window", i.e. eating all your food within 8 hours.
I used to snack all day, thinking that eating many small meals was the way to lose weight. Well, that may work for some folks, but it didn't work for me.
The compressed eating window is giving me great results -- after being stalled for years, I dropped 15 pounds in a month! I don't know if I can keep up that pace of weight loss, but I can easily keep up this way of eating. All I do is wait until 12:00 noon before I start taking in calories, and make sure I'm done eating by 8:00pm. I worked up to it -- I started by waiting till 10:00am for my first calories of the day, then 10:15, then 10:30, and so on.
Now I know that for some folks, skipping breakfast is heresy!
But it's working for me. I start my morning with black coffee or tea or water -- nothing that has calories -- and I pack my lunch for work, usually with last night's leftovers or something simple like boiled eggs, canned soup, canned fruit, etc.
"Engineering the Alpha" advocates eliminating refined carbs entirely for the first two weeks. I haven't quite done that, but I've cut my carbs back and boosted my daily protein intake. Beef jerky and whey protein help me a lot. The book also requires (requires!) a "cheat day" once a week. Twist my arm -- make me eat ice cream!
Hope this helps!