Wal-Mart and other supercenters that sell food now account for 24 percent of the market, according to the most recent annual survey of shopping habits by Hammonds' organization.
Gina Pierson, a music teacher in Columbia, Mo., buys her family's staples at local grocery stores but makes regular trips to Wal-Mart to supplement the weekly shopping list. Like many families struggling to get by, Pierson and her husband, a public school teacher, are adjusting their approach to buying, cooking and eating food. Restaurant meals are now almost a luxury.
"Between food and gas, it's just cheaper to stay home," she said.
In 2007, the FMI survey showed the average number of weekly shopping trips falling below two per household for the first time.
Paula Curtis, a mental health worker in Montpelier, Vt., said her grocery bill has been steadily climbing by $10 to $20 a week. She has cut back on meat, fruit, vegetables and snack food, and buys milk at the gas station, where she said it's cheaper.
"Every time I go, it's more and more," she said. "I make a list, but I don't necessarily get everything on it because I can't afford everything."
Nationwide, a family of four on a moderate-cost shopping plan now spends an average of $904 each month for groceries, an $80 increase from two years ago, according to the USDA.
Those who can't absorb the added expenses are increasingly seeking help from food pantries. America's Harvest, which distributes nearly two billion pounds of food and grocery products each year to more than 200 food banks across the country, estimates that its overall client load increased by 20 percent in the fourth quarter of 2007.
The jump has been even higher at the Central Missouri Food Bank's pantry in Columbia, a college town halfway between Kansas City and St. Louis.
The food pantry served 7,200 people in 2007, an increase of more than 50 percent over two years, said executive director Peggy Kirkpatrick.
Columbia used to be considered inflation-proof because of its high-paying university jobs and proximity to the state capital, 30 miles away in Jefferson City.
"That's not the case anymore," she said.
Shary Auer visits the Columbia food pantry once a month to help extend the family's $800 monthly food budget. The mother of five children, ages 9 to 19, is buying more canned food instead of fresh produce. Portions are smaller around the Auer dinner table, and salads are added regularly to stretch the servings of meat and poultry.
Auer, a part-time postal worker and supermarket cashier, said she fastidiously tracks food prices.
"I watch for sales, save my receipts and highlight what I save," she said.
Not all shoppers are struggling with the changes. At the Whole Foods Market in downtown Seattle, Beth Miller didn't think twice about paying $6.39 for a gallon of organic orange juice, or $4 for a dozen eggs at the store, which specializes in organic and natural foods.
"I'm used to having a small gasp at the cash register," said Miller, who favors local produce and organic food for her husband and 12-year-old son. "We try to be really careful about what we eat."
Among retailers, the surge in commodity prices -- from corn, now in high demand because of increased ethanol production, to wheat that has tripled in price over the past 10 months -- has some industry observers suggesting that higher food prices aren't a temporary fluctuation but instead may be here to stay.
"We don't exactly have a crystal ball," said Whole Foods' Perry Abbenante, a senior global grocery buyer. "But I'm not sure (prices) are going back. We're preparing for a new threshold."