The importance of each God in the Hindu religion is immense and as a result, all the important elements of human life - creation, preservation and destruction are given due importance in the same. One of the toughest parts is played by Lord Vishnu who is the preserver of the universe and He nourishes and performs all the vital tasks and responsibilities needed for sustaining humanity. This is why Lord Vishnu is equated with the status of a mother.
To thank Him for his undying love and prosperity, Thursdays are observed as the fasting days for Lord Vishnu and his incarnations. Pujas are conducted using milk, ghee, etc. The devotees need to eat food made from milk products only once on this day.