Complex sentence: The 5:2 diet, or fast diet, is a diet which involves calorie restriction for two non-consecutive days a week and unconstrained eating the other five days, which originated and became popular in the UK, and spread in Europe and to the USA.
Split into simpler sentences: The 5:2 diet, or fast diet, is a diet which involves calorie restriction for two non-consecutive days a week and unconstrained eating the other five days. The diet originated and became popular in the UK, and spread in Europe and to the USA.