Well fructose was a rarely part of the human diet and is converted to fat by your liver. Sugar is 50% glucose and 50% fructose. When your body get's a hit of glucose it releases insulin that tells your body not to burn fat but use up the glucose. So that fructose gets stored away. Ironically healthy fruit smoothies are exceptionally bad :D

Yes a country's transport policy has an impact. Netherlands has an obesity rate of 1.6% in boys vs 16% in the UK. So getting your kids cycling/walking to school is of massive benefit to the long-term health of your nation.

You still need to deal with the wrong type of calories being delivered into your population.