Ekadasi is a Sanskrit word, which means ‘the eleventh’. It refers to the eleventh day of a fortnight belonging to a lunar month. There are two fortnights in a lunar month—the Poornima and Amavasya. So, Ekadasi occurs twice in a month. The special feature of Ekadasi, as most people know it, is a fast, abstinence from the diet. According to scientific research, it is known that the air pressure on the earth varies to extreme limits on both the new moon (Amavasya) and the full moon (Purnima) day. This is because of the orbital path combination of the sun, moon, and earth.
This can be observed by the change in the nature of the tidal waves on the new moon and full moon days. The waves are very high and rough, but from the next day onwards, the waves become calm, an indication that the pressure has also receded. Now, based on this fact, the significance of Ekadasi fasting can be explained in 2 ways:
1)It takes about 3-4 days for the food that we eat today to reach our brain (for the brain to understand the food intake). Now, if we eat light/fast on Ekadasi days, that intake will reach the brain correspondingly on the New moon/full moon day. On both of these days, the earth pressure is at its maximum, thus leading to an imbalance in everything, including ones thought process. So, if the input to the brain is at a minimum, the chances of the brain indulging in any wayward activity due to the high-pressure imbalance also becomes minimum. People in asylums behave weirdly during ekadashis due to this same lunar activity.
2) Another explanation for Ekadasi fasting is that compared to any other day of the moon cycle, atmospheric pressure is lowest on Ekadasi days. Thus, this is the best time to fast and cleanse the bowel system. If we fast on any other day, the high pressure/strain may damage our system. Thus, it is advisable that after fasting on Ekadasi, on the immediate next day (Dwadasi), we should get up early and eat as soon as possible.