This article on jet lag suggests that what people are really experiencing after long flights isn’t jet lag so much as altitude sickness since the cabin of planes are pressurized to resemble 8,000 feet. (One can add as causes prolonged sitting, dehydration, and maybe other factors, too.) If this is so, then there is a simple way to test it. Compare reactions to a flight east or west to a flight of the same length of time going north or south. The reason is that while the former flight crosses time zones and thus disorients the passenger, the latter does not. It stays in the same time zone, so there is (or should be) no disorientation.
My first trip abroad was to Brazil, and I don’t remember any jet lag. I took a short nap after reaching my hotel, but then I had had hardly any sleep on the plane even though it was an overnight flight, so that was natural. The worst jet lag for me is when I leave the U.S. for Europe in the evening and get off the plane at what is around 7 AM for them. Since I don’t usually get much sleep on these flights, I feel as though it is 2 in the morning. Leaving before noon and getting there in their evening works much better since then I can check into a hotel and go to sleep and wake up at a normal hour feeling refreshed. Also, going west seems to work better than going east, though flying to Taiwan seemed to bring on plenty of jet lag.
My dream isn’t so much to eliminate jet lag as to get a plane that can go between New York and London in two hours. That would eliminate a lot of the pointless and uncomfortable sitting for so long.