This would end the "but it's expensive to eat healthy" and might encourage poor folk to start eating more nutritious meals. Only fresh produce, no frozen veggies.
Its not that fresh fruits and veggies are too expensive, its that food in a can is convenient.
When mom and dad come home from work, its easier to fix little johnny a can or ravioli then it is to fix a fresh cooked meal.
Our whole system needs an overhaul to fix a lot of our problems.
A few years ago there was a discussion in the news if all of the women in the US would stay at home with the family, this would create a workforce deficient, and wages would have to go up.
I have nothing against women working, but when both parents went into the workforce, this drove the number of available workers up, and drove wages down.
There have been theories that womens lib did more damage to the family then ever intended. Its one thing for women to get an education and enter the workforce, its a whole other thing for companies to have people begging for a job.
To fix the obesity issue and junk food issue, the man or woman of the household should stay at home and take care of the nest. This would reduce the number of people looking for jobs, drive up wages to attract available workers, and ensure someone is at home to take care of the kids.
~ EDIT ~
If you want to subsidize something, give a tax break to people who plant a home garden and grow their own food.
If you have a farm, you can write seeds, fertilizer, farm tools off your income taxes. But everyday people who live in the suburbs need some kind incentive to grow their own food.
The US needs to return back to a simpler lifestyle, and part of that means growing your own food. Why should the focus be on buying food from the grocery store? By buying food, people are not learning anything. We need to get people back to planting, growing and eating their own food.