According to Imam Khomeini, there are subdivisions for fasting which both are not considered as accepted for the GOD's feast.
1- The religiously correct fast which is apparently in accordance with religion, the one who fasts avoids things that vitiate the fast and refuses drinking alcoholic drinks. The fast is correct itself but this is not accepted because its acceptance is different from its religious rectitude.
2- The accepted fast, the sense of the fast is not refusing to eat or drink. One should stop doing sins. This is the basic principles of fasting. Eyes, ears and the tongue should be made refusing to do sins. One should remove hatred and other ugly satanic adjectives. One should do his duties purely in order to enter the divine feast. If there were no difference in one's manner then it would be clear that his fast was not accepted.
The Greatest Jihad (Combat with the Self), Text, Page: 23