Yesterday I did a 26hr fast (no food except a cup of coffee with a tbsp of half/half and green tea with a tbsp of almond milk, started 4pm Friday and finished 6pm Saturday). When I woke up Saturday morning, drank 2 large glasses of very cold water and hit the head soon after. Broke my fast with BBQ beef brisket, green beans, smoked jalapenos and some cheese grits.
This morning, 2 large glasses of cold water in the morning and about an hour later it was bathroom time. Coconut oil, cocoa, and almond butter for breakfast, an hour long walk with my wife, and a snack of ground beef, hot sauce, and sour cream at 3pm. A couple hours later nature called again.
In summary, zero problems whatsoever.