I actually just did this and had a great experience. Two long flights and a long layover in between, just kept up water intake and all was good :)
I actually ended up feeling better than if I was to eat the airplane food, I think.
I fast on the plane all the time, and have been going on long 12 hour trips across the globe.
Usually that fast will carry me forth the next few days.
Zero nausea, in fact I feel way better fasting on the plane than eating their crap food.
I wasn’t fasting for that long but flying fasted is awesome. I was stuck in an airport last week for a few hours. Before I’d be stressed about finding something I could eat. It was great not to have to worry about that or about the awful airplane meal.
If you’re worried you can take something in case you feel really awful and need to break your fast.
I sort of do this! I haven’t been on really long flights, but I dont eat anything they give on airplanes. I do take an apple or other hard fruit to counteract my nauseousness just in case. Honestly, I don’t feel a desire to eat plane food anymore since changing my diet to whole foods.
I’m an Airline Pilot and routinely fly while fasting. Just make sure you’re not deficient in your four salts (Sodium, Magnesium, Potassium, Calcium). Drink one can of water per hour of flying since the pressurization of the aircraft causes the air to be as dry as the Saharan desert.