3. 5:2 Diet - loved by Jennifer Aniston, Beyonce and Phillip Schofield
How it works: Eat normally for five days and 'fast' for two, cutting down your calorie intake to just a quarter of the usual daily amount. This adds up to 500 for women and 600 for men. It's been one of the most popular diets of the last year.
The expert says: “Grab yourself a 5:2 cookery book for inspiration and you can still enjoy gourmet food even on your 'fast' days off. It's also one of the few that's had proper medical research done into it.”