American Express ( AXP) placed a lot of blame on the weakening economy when it posted its big earnings miss Monday evening. But one factor that also bears mentioning is the credit card company's rapid growth in consumer lending over the past few years. Shares of American Express fell 7% Tuesday, as Wall Street worried that high gas prices and falling housing prices are causing high-end consumers to cut spending or miss payments on their credit cards. "Fallout from a weaker U.S. economy accelerated during June with consumer confidence dropping, unemployment rates moving sharply higher and home prices declining at the fastest rate in decades," said Kenneth Chenault, the credit card company's chairman and chief executive. "Consumer spending slowed during the latter part of the quarter and credit indicators deteriorated beyond our expectations." In turn, American Express added $600 million to its U.S. lending credit reserves; this caused American Express' earnings to fall 37% from a year ago to $655 million, worse than analysts had expected. Chenault told investors the fallout was evident across all of the company's consumer segments, even the "longer-term super prime" card members. Plummeting housing prices and record gas prices were among the factors American Express blamed for its weak results. Missing from the earnings call, however, was discussion about how American Express' rapid lending growth over the past few years is now coming back to haunt its business.