Welcome to Health Reform Watch, Sarah Kliff’s regular look at how the Affordable Care Act is changing the American health-care system — and being changed by it. You can reach Sarah with questions, comments and suggestions here. Check back every Monday, Wednesday and Friday afternoon for the latest edition, or sign up here to receive it straight from your inbox. Read previous columns here.

Lyric Henry, 1, passes by healthy eating/drinking options at Weso Mini Market in Philadelphia
(Jahi Chikwendiu /The Washington Post)

Across the country right now, hundreds of millions of dollars are being spent on an effort to eradicate so-called "food deserts," urban and rural areas where its difficult, or even impossible, to purchase fresh, healthy food.

Philadelphia has, arguably, been the epicenter of that movement. Since the late 2000s, the city has invested millions in building new grocery stores and adding healthy food options to corner stores in lower-income areas of the city. Hundreds of stores have gotten on board with the movement, with corner store owners selling apples and oranges alongside their more-standard chips and candy. The city has used funds from Obamacare's Prevention and Public Health Fund to further bolster these types of programs.

But while Philadelphia residents are noticing the new grocery options, they're not actually eating any healthier, according to a new study in the journal Health AffairsThe paper is important because it's one of a small handful of academic studies that looks at what happens to eating habits before and after new grocery options become available. And it shows that, six months after two grocery stores opened in Philadelphia food deserts, there was no noticeable difference in body-mass index or fruit and vegetable consumption.

Up until now, though, there have been exactly two studies exploring what happens to fruit and vegetable consumption when new food retail options get introduced into food deserts — neither of which were conducted in the United States. Both came out of Britain in the mid-2000s and showed mixed results as to whether, when new food options get introduced, if neighborhood residents take to them — and if, as a result, they get healthier.

In this study, researchers looked at over 1,000 Philadelphia residents from different city neighborhoods with similar demographics. Some had a 41,000-square-foot supermarket put into their neighborhood, and all lived no more than 1.5 miles away from the grocery store.

People noticed that the new grocery store had shown up. "The new supermarket appeared to have a positive impact on perceptions of food accessibility for residents in the intervention neighborhood," study authors Steven Cummins, Ellen Flint and Stephen A. Matthews write. "Respondents perceived grocer choice and quality and fruit and vegetable choice and quality to have improved, and the cost of fruit and vegetables was perceived to have decreased."

But only about a quarter — 26.7 percent — of those who lived near the new grocery store began using the supermarket as their main food source. Among those who did adopt the new grocery store, there was no significant improvement in body-mass index or fruit and vegetable intake.

"This indicates that simply providing new food retail stores is insufficient to encourage the adoption of new stores as residents' main food stores," the study authors write.

The study only looks six months out after the new supermarket arrived, so it's possible that changes could surface at a later point, as more residents migrate toward the new grocery store. If anything, the new Health Affairs  study mostly shows how little we know about whether expanding access to healthy food can have a meaningful, public health outcome on measures like fruit consumption and body-mass index. To date, no research has shown a causal relationship between expanding access to healthy food and reduced obesity rates.

As to why its so tough to change eating habits, there are a few theories floating around in the public health space. One is that grocery stores don't sell exclusively healthy foods — it's just as easy to buy candy as it is to buy carrots, and maybe even easier, if the candy is less expensive. Others question whether proximity is a good measure for access; one researcher at the University of Washington has shown most people don't actually shop at the closest grocery store.

It's possible that, in the long-term, interventions like grocery stores do show a positive impact on eating habits. When public health officials talk about expanding access to healthy food, they describe it as a necessary but by no means sufficient first step. There's no way to help people eat healthier, after all, if they don't have access to healthy foods. Whether that theory ultimately plays out in practice though remains to be seen.

KLIFF NOTES: Top health policy reads from around the Web.

Arkansas' Medicaid expansion experiment is on the ropes. "The Arkansas’ experiment, known as the 'private option,' marks the first large-scale attempt to enroll Medicaid recipients into the same private health insurance plans that any consumer might buy in the health law’s online insurance marketplace. That’s different from how Medicaid typically works, where enrollees must join state-operated programs or private managed care plans designed exclusively for the poor — and which pay doctors less, sometimes a lot less. As a result, private option enrollees like Fant will have access to a larger network of doctors and hospitals than is usually available through Medicaid." Phil Galewitz in Kaiser Health News.

The White House is quietly allowing some enrollees to switch exchange plans. "The Obama administration has quietly reworked rules and computer code for HealthCare.gov to try to stem an outpouring of discontent by some Americans who have discovered that the health plans they bought do not include their old doctors or allow them to add new babies or spouses. Under changes that have not been disclosed to the public, the government will temporarily allow consumers who have gotten coverage through the new online insurance marketplace to switch health plans to a limited degree." Amy Goldstein in The Washington Post.

California is pulling an error-riddled provider list from its health exchange. "Admitting it gave some consumers bad information, California's health insurance exchange pulled its physician directory for having too many errors. Covered California made the move late Thursday amid growing frustration among both consumers and doctors over inaccurate information about insurance networks in the state marketplace." Chad Terhune in the Los Angeles Times.