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.
One important benefit is that intermittent fasting seems to be easier to follow than continuous calorie restriction, at least for some people. One study showed that the 5:2 diet caused weight loss similar to regular calorie restriction. Additionally, the diet was very effective at reducing insulin levels and improving insulin sensitivity. You just need to dramatically cut back carbohydrates two days a week and try to eat sensibly the rest of the time.