Antonia Williams is part of a slow, quiet food revolution. After battling obesity for much of her adult life, the 26-year-old lifelong Bayview resident did some research. "I realized it had a lot to do with the food I consumed," she told us. "As a result of growing up in the neighborhood, I suffer from obesity. I'm overweight because of the lack of options for good healthy food."

"It's what I grew up on, McDonald's and a lot of fried food for dinner," she recalls. "The grocery stores in the area were very limited in what they offered. I believe my parents weren't as educated or aware" about health and nutrition.

Williams managed to escape this bad foods trap, change her personal diet, and now works as a "food guardian" for the nonprofit Southeast Food Access (SEFA), helping to bring more nutritious fare to the Bayview.

The complex of challenges Williams faced simply to eat well—the fast food all around her, the dearth of grocery stores, and lack of awareness—reflects the array of systemic barriers to good food that keep tens of thousands of San Franciscans in chronically poor health.

Under the weight of recession and double-digit unemployment, San Francisco's chronic food divide has grown deeper and wider. From regions of the city like Bayview, Excelsior, and other Southeast neighborhoods, to seniors surviving on marginal fixed incomes, to the city's swelling unemployed and underemployed who rely on food pantries, access to fresh food is a daily geographic and economic battle.

Roughly one in five San Franciscans each day has no reliable source of adequate sustenance and must scramble for food from soup kitchens, food pantries, or other "emergency" supplies that have become a structural part of the city's food system, according to the San Francisco Food Bank.

Each month, more than 100,000 families rely on the Food Bank to help feed themselves — nearly double the amount from 2006. Economic recession has dramatically increased the number of city residents using food stamps (known as "CalFresh") each month, rising from 29,008 in 2008 to 44,185 in 2010.

Yet even that rise belies a far deeper need: only 47 percent of those qualifying for CalFresh are actually accessing benefits, according to a data analysis by California Food Policy Advocates; at minimum, more than 40,000 additional city residents are entitled to get this help, and thus eat better.

Across the city, parallel economic and food divides compound one another, spelling serious trouble for people's basic nutrition and health — in turn depleting their energy, cognition, and ability to do everything from succeeding in school to getting a job.