Absolutely.  The program is designed for 21 days to help you develop new healthy habits and see transformations take place, but if you can only do 7 or 14 days then that is better than none!  Each of the shopping lists and recipes are split up into separate weeks so you can start with 7 days and keep going if you are feeling motivated!  Because you have access for an entire year to all the materials, you can restart or continue as long as you would like.