When you look at the obesity numbers:
US 36%, New Zealand 31%, Canada 29%, Australia 29%, UK 28%, Israel 26%, Ireland 25%
Thailand 10%, Indonesia 7%, China 6%, Philippines 6%, South Korea, 5%, Vietnam 2%
Vietnam's life expectancy will overtake the US in the next 10-15 years as well most likely (they're about three years behind). In most cases if you prevent people from starving or suffering serious malnutrition, provide a basic level of healthcare & sanitation, and have single digit obesity levels, you'll almost automatically see 75-80 year life expectancies.
South Korea's life expectancy went from 65 years, to 82 years currently, from just 1980 to 2015. They passed the US around 2003. South Korea's GDP per capita was $14,000 at that time, versus $40,000 for the US. One would expect China to have no problem replicating that.
It's a small wonder life expectancies in the developed, high obesity countries are as high as they are. The US is no doubt expending hundreds of billions of dollars extra per year on healthcare as a consequence of its obesity level (cancer, disability, diabetes, etc).