I did a masters (don't recommend) in Human Factors and did my big project on just this subject. Long story short....you'll never adapt. All you can do is mitigate. To a further extent....even working nights in and around your home time zone is better for you than long haul schedules. But neither is good. If you can manage it smartly (takes a lot of self discipline) then you can make out OK. Personally, when I kicked the cargo schedules and adopted a regular circadian rhythm.... I lost a bunch of weight, dropped my blood pressure so low I had to go off my meds, and lowered my blood sugar from pre-diabetic to middle of the normal range. The last two are surely due in large part to the weight loss. A lot of my co workers were better than me at managing it....even though I should have been the poster boy for long-haul self care (I just wasn't). The common 24 hr layovers make it *very* difficult for you to be rested and healthy.