New Jersey Gov. Chris Christie’s decision to stay out of the Republican presidential race means that the American people will be spared months of discussion about his ample waistline and the bad example it sets. Nonetheless, with first lady Michelle Obama urging everyone to get moving, obesity remains a political hot potato, or maybe a tater tot. Below, a helping of skepticism about the causes of Americans’ poor eating habits — and the effectiveness of political fixes.

1. People in poor neighborhoods lack access to fresh fruits and vegetables.

Walk into nearly any supermarket in the United States, and you are immediately confronted with abundance — bok choy, mangos, melons and avocados from across the globe — where a couple of varieties of apples and carrots once struggled to fill shelf space.

But not everyone has easy access to this fruity phantasmagoria. If you’re picking up ingredients for dinner at a gas station or a convenience store, you probably live in what eggheads have taken to calling a “food desert” — an ill-defined concept with powerful policy implications. A commonly cited 2009 statistic from the U.S. Department of Agriculture has 23.5 million Americans living in poor urban and rural areas with limited access to fresh food.

Making those food deserts bloom is a centerpiece of Michelle Obama’s anti-obesity agenda. This January found the first lady smiling for the cameras with Wal-Mart executives in Southeast Washington and declaring herself “more hopeful than ever” as she tours the nation’s produce sections.

But the prevalence of food deserts is almost certainly overstated. Not having a supermarket in your Zip code isn’t the last word in access to healthy food. According to the USDA, 93 percent of “desert” dwellers have access to a car. And farmers markets, often overlooked in surveys of rich and poor neighborhoods alike, have tripled since 1994.

Still, it does seem reasonable that making it easier to buy fresh food would improve what people eat. However, a study published this year in the Archives of Internal Medicine, the first to measure the impact of access to fresh food on diet, followed 5,000 people for over 15 years and found something surprising: Proximity to a grocery store or supermarket doesn’t increase consumption of healthy food. That suggests that a lack of convenient leafy greens isn’t the problem. Dinner menus are the product of subtle and pervasive food cultures, which can’t be tweaked from the East Wing.

The primary beneficiaries of tax incentives and other nudges aimed at abolishing food deserts are big grocery chains, not poor shoppers.

2. Advertising forces people to make unhealthy choices.

Television-bound children, their eyes awhirl with images of Tony the Tiger and his high-fructose friends, haunt the debate about junk-food advertising. And any parent who has ever experienced a 2-year-old’s grocery store meltdown would certainly like to have someone to blame. But the Institute of Medicine, an arm of the National Academy of Sciences, has concluded that “current evidence is not sufficient to arrive at any finding about a causal relationship from television advertising to adiposity [excess weight] among children and youth.” Similar findings hold true for adults.

We don’t need advertisers to tell us that candy is delicious. Humans were big fans of fat and sugar long before the idiot box was invented. We’re programmed to go for the good (bad) stuff. Sure, Kellogg’s and General Mills have big advertising budgets, but they’re nowhere near as powerful as Darwin. Cracking down on advertisers gives politicians a scapegoat, but it doesn’t make kids, or their parents, healthier.

3. Eating healthy is too expensive.

A dinner of hot dogs and Devil Dogs is undeniably cheap. But a bowl of beans and rice with a banana on the side is cheaper. A survey by the USDA found that, by weight, bottled water is cheaper than soda, low-fat milk is cheaper than high-fat, and whole fruit is cheaper than processed sweet snacks. Preparing a big pot of lentils for the week may be not be glamorous, but it’s much cheaper and not much more time-consuming than cooking up frozen pizza or mac and cheese.

The New York Times’ Mark Bittman — no fan of Frito-Lay — writes that the idea that junk food is cheaper than real food is “just plain wrong” and that blaming unhealthy habits on cost is incorrect. People who eat lots of unhealthy food aren’t doing so because they lack cheap, healthy options. Instead, it’s because they like junk food. Making junk food comparatively more pricey by tacking on taxes — a proposal that has been revived many times by Yale’s Kelly Brownell (and recently made into law in Denmark) — mostly means that people will pay more taxes, not eat more kale.

4. People need more information about what they eat.

It’s hard to argue against rules that give consumers more information. Perhaps for that reason, proposals to require restaurants to jam calorie, fat and other nutrition statistics onto already crowded signs and menus pop up over and over — most recently as part of the health-care reform law — despite the fact that virtually all major fast-food chains already provide such information on handouts and online.

Knowing that a chocolate shake at Shake Shack has 740 calories doesn’t stop me — or the first lady— from ordering one occasionally. We’re not alone: Studies consistently find that menu labeling doesn’t result in healthier choices. A recent study from Ghent University in Belgium found that labels made no difference in the consumption patterns of students there, backing up a 2009 New York University study that found no improvement in poor New Yorkers’ eating habits after the introduction of mandatory menu labeling in the Big Apple.

5. There are too many fast-food restaurants in low-income neighborhoods.

In many urban neighborhoods, it’s easier to get permission to open a sex shop than a Taco Bell, thanks to aggressive policies by local zoning boards. But zoning out fast-food restaurants in cities is a lost cause — they are probably already too thick on the ground for new restrictions to alter the culinary mix. The same study that found no effect on diet from increased access to fruits and vegetables also found that proximity to fast-food restaurants had only a small effect, and it was limited to young, low-income men.

In a commentary accompanying the study, Jonathan E. Fielding and Paul A. Simon of the Los Angeles County Department of Public Health wrote that “policy efforts to reduce access to [junk food], though politically challenging, will likely have a greater impact on reducing the obesity epidemic than efforts focused solely on increasing access to fresh produce and other healthy options.” “Politically challenging” is code for “virtually impossible.”

And for good reason. Eliminating access to fast food and other junk food means taking away choices, something Americans don’t tend to like, even (or perhaps especially) when it’s for their own good.

Katherine Mangu-Ward is the managing editor of Reason magazine.

Read additional Outlook coverage of food and politics: Eric Schlosser on “Why being a foodie isn’t elitist” and Janet Poppendieck on “Five Myths about school food.

Read more from our “Five myths” archive.

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