It seems to be conventional wisdom that poor people are more likely to be obese because it's too expensive to eat healthy. I saw this meme come up on Facebook a week or two ago, in reference to some op-ed I didn't bother reading, and one of the other comments was that a 5-lb bag of frozen french fries is cheaper than a 5-lb bag of potatoes.
I questioned it then, because I'd just bought a 10-lb bag of potatoes for under $3. Of course, after posting the comment I realized I really couldn't be too sure, because I don't think I'd ever actually bought a 5-lb bag of french fries before.
I remembered to check it out yesterday when I was at HEB. I bought two 5-lb bags of russet potatoes (they're little ones, not the big baking potatoes) for $1.49 each, or $2.98 total. Then when we were in the frozen food section I checked the price on the big 5-lb bag of french fries, store brand, and it was $4.68. Huge difference.
I strongly suspect the story is similar in other things, and influenced by merely comparing the price on the shelf, as opposed to considering servings and utility. Sure, a box of old fashioned oats might cost more than a bag of Malt O' Meal cereal (although, I actually don't think it does; I'll check when next I go to the store), but with that you can make oatmeal, muesli, oatmeal cookies, granola, etc. (It also makes a good sub for breadcrumbs when it's meatloaf time.)
Chances are that belief also suffers from a misunderstanding about what constitutes healthy. For instance, organics are considerably more expensive than conventional products, but pesticides can be cleaned off produce without much trouble and, marketing hype aside, they do not have better nutrition profiles. Even considering only conventionally-grown produce, however, cheaper can often be at least as healthy if not moreso--the old theory that canned produce is less nutritious is probably a fallacy, given that "fresh" produce is often harvested well ahead of when it should be so that it doesn't spoil while in transit. Theory goes that canned vegetables are usually canned pretty close to wherever they're grown, so the nutrients have a better chance of being ('scuse the pun) preserved. Granted, that doesn't address the issue of how seldom canned veggies are at all palatable.
I know when I am looking to cut my grocery budget, things like bacon and cheese and milk are the first things to go, along with most convenience foods. Much as I love bacon, it's hardly the healthiest thing you can eat. Milk is healthy enough, but there are other, better, sources of pretty much all the nutrients it provides. (Yes, I include Vit. D--it's called sunlight, people.) I only eat tofu when I'm broke. I actually like it, but it takes a backseat to meat when I have the dinero.
Come to think of it, meat is another of those things I think sometimes get short shrift when it comes to what's really healthy. Skinless chicken breasts are held up as the ideal lean meat, but chicken thighs have a comparable nutrition profile, and I can generally buy them for $1 to $1.19/lb, rather than $2-something for the chicken breasts. (I have to be vague here since I don't recall the last time I actually bought chicken breasts.) Hell, you can get a whole chicken for usually less than $1/lb, and in theory get two or three meals out of it. (I've only ever managed that when I make soup.)
So, why do poor people tend to not eat as healthfully? I'm betting on two main factors: time and perception of difficulty.
Time. A lot of the working poor work more than one job, or ride the bus, or work odd and/or long hours. Even though I wasn't working at the time, back when the girls were going to the charter school and I to on-campus classes and we were doing this all on the bus, on a short day (defined as, coming straight home from their school) we were gone 11.5 or 12 hours. Add in 8 to sleep, and that is not a lot of time for food prep or anything else.
And that's where the second factor comes in. Perception of difficulty. It's really not hard to toss together a dinner consisting of, say, baked chicken, rice, and zucchini, but for some reason making dinner is shown as a choice between hot dogs & tater tots or a three course gourmet meal. There's a frickin' TV channel devoted to promoting overly-complicated meals. (Look, Alton Brown produces the yummiest stuff ever, but it is crazily labor-intensive to do things his way. I'm not going to bust out the ironing board to make ravioli from scratch anytime soon.) So I don't doubt that there are a lot of people out there who default to the crap food because it seems as though the other option is much more labor intensive than the truth would have it.
Note, please, that I do realize there are other factors. (Some day, maybe, I will rant about how the crap kids are fed in school lunches plays into the "my kids will only eat chicken nuggets and french fries" nonsense.) But I think those are the two big ones.