Most people think of people lining up at food pantries and soup kitchens as an urban phenomenon. But in Alameda County, which has one of the highest rates of food insecurity in the Bay Area, an increasing number of people living in the suburbs are also having trouble affording food. That includes Livermore, a city in the Tri-Valley area that’s better known for its wineries.

“When people think of homelessness and poverty, they don’t think of this area,” said Clare Gomes of Open Heart Kitchen in Livermore, which in the past five years has doubled the number of schools providing free bagged lunches for children to take home on the weekends. “They think of it as being affluent, but there also is the opposite extreme. It’s more hidden than in Oakland and San Francisco.”

As low-income Alameda County residents get displaced from the urban center, rates of food insecurity are increasing in outlying areas like Hayward, Fremont, Dublin and Pleasanton, according to a new report by the Urban Institute, a Washington economic and social policy research organization.

The problem is compounded by the high cost of living even in suburban areas, leaving many residents without enough money for groceries by the end of the month, food policy experts say.

“There’s a lot more households out there that are feeling stress. And they’re not necessarily households that the food bank has ever served, and they might not think of themselves as food insecure,” said Elaine Waxman, an author of the report commissioned by the Alameda County Community Food Bank to find areas and populations it could serve better. “The purpose of this is not just to think about today, but can we think about what might be coming in the future?”

The report sifted through data from the U.S. census and Feeding America, a national network of food banks, to look for rates of poverty and other indicators of food insecurity such as poor credit and unemployment. In addition to identifying geographic areas where there’s a risk of food insecurity, the report also looked at the correlation between food insecurity and high rates of debt and credit problems; lack of health insurance; and poor mental and physical health.

“Often food banks and food pantries are on the front lines. They are the early indicators of the growth of economic insecurity or distress in these communities,” said Elizabeth Kneebone, research director for the Terner Center for Housing Innovation at UC Berkeley.

The report identified almost 200,000 Alameda County residents with low or very low food security, which means they have answered yes to survey questions like “Did you or the other adults in your household ever cut the size of your meals or skip meals because there wasn’t enough money for food?” In addition, the report identified an additional 130,000 residents who are “marginally food secure,” meaning they are at risk of not having enough money for food.

Food insecurity in Alameda County is 12.2%, compared with 12.4% in San Francisco and 8.3% in San Mateo County, according to Feeding America. At a city level, it ranges from 11.5% of residents in wealthy Piedmont to 29.2% in Oakland, according to the report. Though food insecurity is most acute in urban districts, the findings also show large swaths of Hayward, Fremont, Dublin and Livermore where over 20% of residents are at risk of hunger.

“We have seen a real shift in the growth of poverty across the country. What’s been striking about these trends is we’re past a tipping point where there are more poor people in the suburbs than the cities,” said Kneebone, who coauthored a book titled “Confronting Suburban Poverty in America.”

In 2000, an almost equal number of Americans below the federal poverty level resided in major cities (10.5 million) as in the suburbs (10.2 million). By 2017, the number of people living in poverty grew to 14.8 million in the suburbs, more than the 11.6 million in cities.

In the Bay Area, some of the increase in suburban poverty may have to do with rising rents in the cities. An analysis by the real estate website Trulia showed Oakland to have the second-largest rent increase nationwide from 2012 to 2017, when the median rents increased by 51%, from $1,952 to $2,950.

In addition, Alameda County had the largest population growth among Bay Area counties between 2016 and 2017, with Dublin growing nearly 4%, and Livermore and Newark growing almost 1.5%, according to U.S. Census data compiled by the United Way. But even with relatively lower rents in outlying areas, residents who come to food banks are still struggling to make ends meet.

“Our numbers are growing,” said Jennifer Case, a minister at the Well Christian Community Outreach Center in Livermore, which has a food pantry three days a week plus one Saturday a month, serving around 30 to 40 families a day. Case said the clients they serve come from all socioeconomic backgrounds. “They’re single seniors to families of 10, some from as far as Stockton and Modesto.”

Nearby, Open Heart Kitchen provides schoolchildren who qualify for free and reduced lunch extra bagged lunches to bring home on the weekends, in case they don’t have enough to eat at home. Each is filled with enough for two meals — including shelf-stable milk, baby carrots, sunflower seeds, high-fiber muffins and turkey jerky.

In the past five years, Gomes said the organization increased the number of local schools it serves from 14 to 28, to feed about 2,750 children, yet that covers just over half of the kids who qualify.

Kate Cheyne of the Alameda County Community Food Bank said the organization’s goal is to help underserved populations like Livermore’s schoolchildren get more access to free meals or bags of groceries so their families have more money for other expenses.

“We’re very interested in reaching more people and preventing them from slipping even further before savings are depleted,” she said.

This story was updated to correct the number of people who were found to be “marginally food secure” in Alameda County.

Tara Duggan is The San Francisco Chronicle’s assistant food editor. Email: tduggan@sfchronicle.com Twitter: @taraduggan