Are you from L.A.? I live in SoCal and something tells me there isn't a shortage of affordable real estate in South Central.
Here's the real 411 on the situation... The "healthier" alternative to fast food is the grocery store, and folks cooking their own (presumably healthier) meals at home.
But there has historically been a reluctance for major grocery retailers to open stores in South Central. Why? Because they incur significantly higher losses from shoplifting and employee shrinkage in this area. Ordinarily the retailer would raise the prices accordingly to cover the losses, but in the case of retailers who operate over a wide area, they by law must charge the same price for something in one neighborhood as another, otherwise they're breaking the law. What's holding Trader Joe's back from building in South Central isn't the cost of real estate, I guarantee you.
There are small grocery chains which have historically operated only in South Central (Boys, ABC) and they are free to cover these costs with higher prices because they only operate in relatively depressed areas. And actually, they do a pretty good job of catering to the ethnic proclivities of their customers.