I suspect the more food - like the fluid is, the more likely you will get the reflex response. But, I have not experimented. We do have two small snack packs on my airplanes: maui monk pretzels at 60 calories and levy gram crackers at 110 calories. I have experienced gastrocolic reflex with each of them. I do know as one having undergone rectal resection and radiation therapy that once my gastrocolic reflex starts, it is often hard to stop it before it proceeds to full diarrhea which is impossible to control with the sphincter muscle alone. A second opinion I received from a gastroenterologist specializing in low anterior resection syndrome said this likely due to malfunction of Recto-Sigmoid Brake, another autonomic response that starts in the vicinity of where the rectum and sigmoid colon meet - which is the surgery site for low anterior resection, likely damaged by surgery and radiation.

I frequently have other flight attendants ask why I do not eat on airplanes or fast for 18 - 24 hours starting the night before an early trip. As you can guess, it is a complicated explanation that I usually try to avoid