Wal-Mart Stores Inc. offered a weak business outlook Thursday as new economic challenges for its low-income shoppers start to take a toll.

The world's largest retailer said its fourth-quarter profit rose 8.6 percent. But higher gasoline prices, late tax refunds and the payroll tax increase have it wary about the coming year.

Wal-Mart, based in Bentonville, Ark., is considered an economic bellwether because the retailer accounts for nearly 10 percent of nonautomotive retail spending in the U.S. Low- and lower-middle-income people have continued to struggle even as the housing and stock markets improve.

Wal-Mart's latest results, which cover the three months that ended Jan. 31, show that gas prices and the payroll tax increase of 2 percentage points are shrinking the little disposable income they have.

Investors were already bracing for a subdued report after a Bloomberg report published last week leaked an email from a top executive characterizing the first two weeks of February as "a total disaster."

Wal-Mart acknowledged in Thursday's report that February started "slower than planned" but noted that it was largely due to the delay in tax refund checks. For the current quarter, Wal-Mart expects revenue at stores open at least a year at its U.S. namesake business to be flat with last year. That represents a slowdown from the 1 percent increase in the fourth quarter.

The results come a little more than a year after Wal-Mart's U.S. namesake business turned a corner by reemphasizing low prices and restocking stores with thousands of basic items that it had gotten rid of in an overzealous bid to reduce clutter.

During the third quarter of 2011, the division reversed nine straight quarters of declines in revenue at stores open at least a year, considered a key measure of a retailer's health. The U.S. namesake business has now recorded six consecutive quarters of gains since the division rebounded.

But the fourth-quarter gain is below the 1.5 percent increase analysts polled by Thomson Reuters were expecting. Overall, revenue at stores open at least a year rose a modest 1.2 percent, including a 2.3 percent gain at Sam's Clubs. Analysts had expected a 1.8 percent increase.

That growth pace has slowed in recent quarters as it's getting harder for Wal-Mart to lap increases from year-ago gains.

Wal-Mart says it earned $5.6 billion, or $1.67 per share, in the quarter ended Jan. 31. That's up from $5.16 billion, or $1.50 per share, a year earlier.

Net sales rose 3.9 percent to $127.1 billion.

Earnings topped estimates of $1.57 per share, but net sales fell short of the $127.8 billion estimate.

The company says it expects earnings per share to range from $1.11 per share to $1.16 per share for the first quarter. That's below analysts' expectations for a $1.18 per share estimate, according to FactSet.

For the year, Wal-Mart expects earnings per share between $5.20 and $5.40 per share. Analysts expect $5.38 per share, according to FactSet.