As the fortunes of many Americans go, so goes Walmart, so goes the economy.

Even as the world's largest retailer reported an 8.6 percent rise in fourth-quarter profit during the critical holiday shopping season, it offered a weaker forecast for the coming months.

The problem? The poor and middle-class Americans Walmart caters to - and who are big drivers of spending in the U.S. - are struggling with higher gas prices, delayed tax refunds and higher payroll taxes.

Melanie M. Burkhardt, the mother of two teenagers, is one of those people. Burkhardt, a Waycross, Ga., resident, said she's been hit by a double whammy of higher gas prices and the payroll tax hike that has cut her household monthly income by $260.

"This is money we used for things like going to a movie or splurging at Olive Garden. Not anymore," said Burkhardt, a legal assistant.

Walmart is the latest in a string of big-name companies from Burger King to Zale to warn that Americans are being squeezed by these new challenges. But since Walmart accounts for nearly 10 percent of nonautomotive retail spending in the U.S., it is a bellwether for the economy.

"Walmart moms are the barometer of the U.S. household," said Brian Sozzi, chief equities analyst at NBG Productions. "Right now, they're afraid of higher taxes and inflation."

While wealthier households have seen their stock portfolios grow, poor and middle-class Americans have struggled to regain their financial footing since the recession ended more than 3 1/2 years ago. Stocks have roughly doubled since June 2009.

At the same time, while incomes for most Americans have failed to keep pace with inflation since the recession, that's been particularly true for middle and lower-income people.

Median household income, adjusted for inflation, fell 1.5 percent to $50,054 in 2011 compared with 2010, the latest Census Bureau figures available. That was down 8.1 percent from 2007. (The median is the point halfway between the highest and lowest levels.)

But lower and middle-income households fared worse: The share of overall income earned by the bottom 80 percent of households shrank in 2011, while the income for the top 20 percent grew. And in 2012, inflation-adjusted hourly pay barely rose, inching up 0.3 percent.

Another hurdle for lower- and middle-income Americans has been the jump in gasoline prices since mid-January.

Tax changes also have hit lower and middle-income households especially hard. On Jan. 1, Social Security payroll taxes rose 2 percentage points after a temporary cut expired. That sliced about $1,000 from the take-home pay of a household earning $50,000. Since the Social Security tax is levied against income only up to $114,000, it disproportionately affects middle- and lower-income households.

An even larger challenge for many lower-income Americans has been the government's delay in processing taxes and paying refunds. That's because income tax rates weren't set until a last-minute deal between the White House and Congress on Jan. 1. So the IRS pushed back the start of tax-filing season to Jan. 30, two weeks later than usual.

Walmart said February, in particular, has been "slower than planned" largely due to the tax refund delay.