Foodie is a loaded word. Every few months someone starts a Talk topic here on Serious Eats to grouse about it (here, here, and here, for starters). I'm ambivalent about it, finding it useful at times when you've exhausted all other synonyms.
If you're wondering whom to thank or blame for its coinage, look no further. According to etymologist Barry Popik, former New York magazine food critic Gael Greene appears to have used it in print first in 1980:
Gael Greene of New York magazine used the word “foodie” in a story on June 2, 1980, and then used “foodie” several times in 1982 and 1983. There were several London-based citations of “foodie” in 1982 and 1983. It appears that Gael Greene’s 1980 “foodie” and [U.S./British author and food journalist] Paul Levy’s 1982 “foodie” were independent coinages.