A woman passes an advertisement outside a fast food outlet. (Photo by Matt Cardy/Getty Images)

Here's an interesting look by the Rand Corp. (via the Los Angeles Times, which wrote this excellent story) at what happened when L.A. restricted the number of stand-alone fast food restaurants in South L.A.

Nothing. Well, nothing good, if you're interested in public health.

From 2007 to 2012, Rand found, the proportion of overweight and obese people increased across L.A. county, but rose significantly more in the area covered by the ban on new fast food outlets. About 700,000 people, many of them African American, live in those neighborhoods.

The study found that the proportion of obese and overweight people increased from 63 percent to 75 percent over those five years in South L.A., while it rose just one percentage point, from 57 percent to 58 percent, in the rest of L.A. County.

[Why do we still eat this way?]

Nor was L.A. able to keep out the restaurants it was targeting. The ordinance was crafted to apply only to "stand-alone restaurants with limited menus, items prepared in advance or prepared quickly, no table orders and disposable containers," according to the Times. So 17 new fast food outlets that shared space in strip malls opened in the area between 2008 and 2012, the Rand study showed.

Taking on long-established preferences for fast food is a difficult and complicated process, behaviorally and legally. New York last year lost its high-profile attempt to ban huge, sugary sodas, when the state Supreme Court struck down the law. Adding calorie counts to menus hasn't had a dramatic impact on consumer choices so far.

It may be that the South L.A. ban on fast food outlets needs more time to be effective. An unrelated study found a slight drop in obesity between 2009 and 2013 in that area, from 35.4 percent of the population, to 32.7 percent.

[Watercress tops list of powerhouse fruits and vegetables]

Curbing a fast food habit is no easy matter. In "The End of Overeating," former FDA Commissioner David Kessler said the problem is a combination of the addictive nature of salt, fat and sugar added to many foods and social mores that allow the consumption of vast quantities.

Here's a guide from the Centers for Disease Control and Prevention on changing unhealthful eating habits.

Good luck.

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