US obesity rates are around 40% of population. Australia, Canada, UK, it is around 30% of population. Canadian life expectancy is 3-4 years higher on average. UK around 3 years higher on average. Australia around 4-5 years higher

Does the gap in obesity rates fully explain the difference in life expectancy? Or are there other factors at play?

I don't think it actually does, because UK has lower obesity rates than Australia (26-29% versus 32%), yet also lower life expectancy (Australia is 81.1 male, 85.1 female; UK is 78.8 male, 82.8 female)