Intermittent fasting is an eating pattern that involves regular fasting.
The 5:2 diet, also known as The Fast Diet, is currently the most popular intermittent fasting diet.
It's called the 5:2 diet because five days of the week are normal eating days, while the other two restrict calories to 500–600 per day.
This diet is actually more of an eating pattern than a diet. There are no requirements about which foods to eat, but rather when you should eat them.
Many people find this way of eating to be easier to stick to than a traditional calorie-restricted diet
This App explains everything you need to know about the 5:2 diet.

Eat what you want five days a week, send your body to starvation mode for two. The part-time diet that still allows you to eat chocolate cake has hit the headlines and taken off in a big way.
If we were to distill the Fast Diet into a single sound-bite, it would all come down to 5:2. That’s five days of normal eating, with little thought to calorie control and a slice of pie for pudding if that’s what you want. Then, on the other two days, you reduce your calorie intake to 500 calories for women and 600 calories for men.
Since you are only fasting for two days of your choice each week, and eating normally on the other five days, there is always something new and tasty on the near horizon. In short, it’s easy to comply with a regime that only asks you to restrict your calorie intake occasionally. It recalibrates the diet equation, and stacks the odds in your favour.

Calorie count lists and low-carb recommendations so you can adapt meal ideas to suit you