A Dutch study: http://musclemotion.nl/PDF/052-055%20Voedingswaarde.pdf
And an American one: http://www.utexas.edu/news/2004/12/01/nr_chemistry/
Here in Holland we still promote eating 2 pieces of fruit and 2 ounces of vegetables as day. These recommendations were set back in 1986. The amount of vitamin C in apples has declines by 80% since then. An apple a day does not keep the doctor away anymore.
To sum things up: most people can not afford healthy food and choose quantity over quality which can lead to long term, possible permanent damage.
I'm facing the same challenge. I don't have much to spend but am set on eating as healthy as I can. So I save money on a lot of other things. I hardly ever buy clothes, I don't go out but have people come over for a cuppa, I turn off the lights when I'm not in a room, I shower at the gym most of the time, etc. That saves me money to spend on food. I buy most of my fruit and veggies on the market instead of in the supermarket. Yes, even when it rains. It's a lot cheaper, at least, it is here in Holland. And I use my balcony to grow vegetables, strawberries and herbs. This year the harvest was a bit disappointing and it's starting to get colder so it's time to bring some of the pots inside. I am going to plant some new seeds and use the windowsill as a bit of a greenhouse. These are little things one can do but they add up.
I hope this helps people a bit to become more aware and get in good health. You only have one body. Treat it well and it will carry you.