(Below is an extract from an ashirwad, which His Divine Holiness Acharya Swamishree gave, which explains the meaning of oopvaas.)

By looking at the precise definition of the word oopvaas (fasting), the importance of an oopvaas becomes immediately apparent.

"Oop" means near.

"Vaas" means to reside

Thus the word oopvaas refers to residing at the divine feet, i.e. in close proximity with the Lord.

During an oopvaas, one's closeness to God is the most important factor, not the abstinence from food and drink.

Achieving this closeness with God will not just happen. You will have to spend a lot of time and effort to achieve this goal.

On an oopvaas day, time should be spent in the Mandir, doing God's darshan, listening to the katha, singing kirtans and dhoon. Even when returning home, the rest of the day should be occupied with reading our Holy Scriptures in front of the Lord's murti.

Generally, the day of ekadashi (eleventh day of each half of the month) and the months of chaturmaas are favoured for observance of oopvaas. Our philosophy describes us with having 5 gnaan indriyo (senses) and 5 karma indriyo (organs which control these senses). The mind is the controller of all these 10 indriyo and is therefore regarded as the 11th indriya. During an oopvaas, if these 11 indriyo are fed with only God's remembrances and with no other worldly thoughts or desires, the observance of the oopvaas has been truly adhered to. If this control of mind and body and restraint from worldly desires does not occur, then even though you may have abstained from eating, you have not observed an oopvaas. During an oopvaas, all 11 indriyo must become purified.

During an oopvaas day, you should try not to sleep. Lord Swaminarayan says in the Shikshapatri (slok 80), "By having sexual pleasures during an oopvaas day, the benefits of observing the oopvaas are destroyed. In the same manner, sleep during the day also destroys the benefits of an oopvaas."

Observing the rules of an oopvaas not only purifies the indriyo, but also the body becomes de-toxified, and thus its vitality also increases. Fasting has the effects of boosting the immune system. Thus the months of chaaturmaas, when infectious diseases are more abundant, are chosen for the extra oopvaas observances.

All 11 indriyo, food, and daily practices have to be controlled during the day of oopvaas. Only then will the true observance of oopvaas be achieved.