Wal-Mart makes people skinny?

I was waiting in a doctor's office this morning and read this amusing story about how living near a Wal-Mart makes you skinnier.

Yeah, I'm skeptical. I'd have to read the actual research to see if it's controlling for all relevant factors, because if it's just comparing the girth of people near a Wal-Mart versus those far from a Wal-Mart, that's not good enough. For example, if Wal-Mart tends to locate in places where land is cheap (rural and suburban rather than urban) rather than where land values are high (urban, "downtown" locations), well, duh. It's no secret that poorer people eat less healthily and are more likely to be obese.

Nonetheless, this is one of the reasons why economics amuses me so much.