According to science, it takes about 3-4 days for the food that we eat today to reach our brain. Now, if we eat light/fast on Ekadasi days, that intake will reach the brain correspondingly on the New moon/full moon day. Fasting is undertaken to purify the consciousness of its impurities at the gross and spiritual level. The day is extremely auspicious to render and involve oneself in spiritual activities. Fasting gives the system a rest. The physiological system may become overworked due to a little overeating or indiscrimination in diet. Thus the fortnightly Ekadashi fasting gives the system a chance to catch up. We know that the digestive system draws the blood circulation towards the digestive organs. Therefore blood circulation to the head is decreased once food is taken: so we feel sleepy. Thus observance of Ekadashi helps us recharge our brain and mind keeping us more alert, sharp, focused and more aware. On the day after Ekadasi it is called dwadasi, where you eat at least before 10:00 AM. On Ekadasi drink a large amount of water, so then you can feel more full.
Full eating should be avoided and partial fasting on milk and fruits can be taken.
The basic aim is just not to fast but to think of the divine and the pastimes of Krishna by reading his stories. The fast begins with the sunrise on the Ekadasi day and ends with the next day’s sunrise.
Foods that can be taken on the day of ekadasi are: fruits, nuts, olives, milk, ghee, sugar, coconut, ginger and black pepper.
Download Vaishnava Reminder for Ekadasi and More on Android: https://play.google.com/store/apps/detailsid=com.madhava.vaisnava.reminder&hl=en
Windows or Mac or Linux: http://harekrishnacalendar.com/vaishnava-reminder/
It automatically comes up when you start the computer.
Ekadasi Calendar and More IOS: https://itunes.apple.com/us/app/iskcon-calendar/id680532373?mt=8&ign-mpt=uo%3D4
Normal Website That Has Dates for Ekadasi: http://www.drikpanchang.com/vaishnava/vaishnava-ekadashi-calendar.html
Another way to put an ekadasi calendar and more for vaishnavates is this.It works on android,pc, and ios.
How to do it