Up until 2015, Haven, Kansas, a town of just over 1,200 people, had one grocery store: the Foodliner, a mom-and-pop store owned by a local, Dough Nech. Around 225 locals a day would cycle through the store, picking up basics like bagged lettuce and chicken.

That changed when a Dollar General opened in Haven in February 2015. Almost immediately, Nech saw a drop in the flow of customers through Foodliner. By last year, they rang up only around 125 people; sales dropped by 40%, he told The Guardian. This August, the Foodliner permanently closed.

Dollar General is the fastest-growing retailer in the U.S. and it, along with its competitors Dollar Tree and Family Dollar (which is owned by Dollar Tree), have made a killing in recent years by expanding into some of the county’s most vulnerable communities: small, rural towns, and urban, predominantly black neighborhoods. When that happens, dollar stores essentially take over the market, making it impossible for independent local retailers, like Foodliner, to thrive. And in doing so, dollar stores essentially ensure that people living in the areas they target will struggle to access healthy food. While affordable, dollar stores rarely offer any food beyond highly processed options, and in areas where it’s already difficult to find produce and fresh options (often called food deserts), they don’t do much to change the status quo.

New research from the Institute for Local Self-Reliance, a nonprofit that supports local alternatives to entrenched economic systems, finds that since 2011, the number of dollar stores has grown from 20,000 to nearly 30,000. They outnumber Walmarts and Starbucks, combined. They feed far more people than Whole Foods, the poster-child for healthy grocery stores. ILSR reports that Dollar General and Dollar Tree expect to expand to 50,000 stores in the next several years.

“Although dollar stores sometimes fill a need in places that lack basic retail services, there’s growing evidence that these stores are not merely a byproduct of economic distress. They’re a cause of it,” write ILSR co-authors Marie Donahue and Stacey Mitchell. “In small towns and urban neighborhoods alike, dollar stores are leading full-service grocery stores to close. And their strategy of saturating communities with multiple outlets is making it impossible for new grocers and other local businesses to take root and grow.”

Mitchell and Donahue point particularly to Tulsa, Oklahoma, where more than 50 dollar stores are concentrated in the city’s black neighborhoods to the north, and largely skirt the whiter areas of the city. The north side of the city lacks a full-service grocery store, and dollar stores have sprung up to fill in gaps left by long-standing disinvestment in black neighborhoods, where larger supermarket chains are still hard to find. But ILSR found that the proliferation of dollar stores are not helping the quality of life for residents–people in north Tulsa have a 14-year lower life expectancy than people in the rest of the city, and it’s in part due to access to healthy options.

In both urban neighborhoods and rural areas, when dollar stores start opening, they spell economic trouble. Dollar General and Dollar Tree stores only employ around eight people, and small independent groceries employ an average of 14, according to federal data. David Procter, an expert on community development and director of the Rural Grocery Initiative at Kansas State University, told ILSR that the effects of local stores disappearing are even broader. “The problem is that if the grocery store closes, this impacts the town in a big way. Our research shows grocers are barometers for other businesses in town: as goes the grocery store, so goes other independent businesses in that community.” Additionally, locally owned groceries have a better sense of community needs than large national chains, and would often offer delivery of fresh food to seniors or people with mobility needs who couldn’t easily access stores. Dollar General and Dollar Tree do not.