People from skinnier countries move to the US and get fatter. It's not willpower keeping other countries skinnier (to the extent they still are, even) so it'd be weird to expect that to work for people who've always lived here.
But you can hack biology, or just be born with lucky biology, and beat environment.
You hypothetically can with willpower too, but in practice, over any meaningful sample size and longitudinally, no you can't.
Biology over environment over willpower.
People from skinnier countries move to the US and get fatter. It's not willpower keeping other countries skinnier (to the extent they still are, even) so it'd be weird to expect that to work for people who've always lived here.
But you can hack biology, or just be born with lucky biology, and beat environment.
You hypothetically can with willpower too, but in practice, over any meaningful sample size and longitudinally, no you can't.
Same with alcohol, cocaine, meth, etc. If it’s not available, you cannot harm yourself with it. If it is available, you may not be able to resist.