The 49-year-old singer will be giving up the sugary snacks for 40 days to raise money for the Scottish Catholic International Aid Fund Wee Box campaign.
Susan will join her fellow Catholics to give up something they enjoy during the religious period.
The money that they have saved is then put into a SCIAF Wee Box and it will be given to the charity over Easter. It will then go towards aid projects in some of the world's poorest countries.
Paul Chitnis, from SCIAF, said: 'Susan's involvement will help us to combat global poverty.'