Probably more of a city design problem. Even modest exercise like walking your 8000 steps has a huge effect size. Exercise is a much more effective intervention than diet alone. America is designed to make people fat. There are places in America that don't have sidewalks. Sidewalks! It'd be funny if people weren't dying from it
There’s a fascinating case study on how this happens - Mexico had population much less overweight than USA until NAFTA was agreed to and cheap USA processed foods began inroads so that now Mexico has close to the same obesity issue that the USA has.