Despite some pessimism in January about its first quarter, NutriSystem Inc. reported strong earnings yesterday for the quarter ended March 31.

The Horsham diet company, citing increased sales to men, said net income was up 70 percent to $37.9 million, or $1.04 a share, from $22.3 million, or 60 cents a share, in the 2006 quarter.

Late in January, its stock fell after it forecast quarterly earnings of 82 cents to 86 cents a share. Analysts were predicting earnings of 96 cents a share.

Unusually warm weather in January worked against the company, which markets its products heavily on television, said Michael J. Hagan, chairman, president and chief executive officer. Potential customers, he said, were less likely to be watching TV.

Business picked up later, with an especially strong showing from men and former customers coming back for a low-cal tuneup.

NutriSystem started offering a new line of men's meals in January 2006, Hagan said. The share of male customers rose from 18 percent in first-quarter 2006 to 35 percent this year.

As its customer base has grown, the number of NutriSystem dieters who return to company meal plans has been growing as well. They accounted for about 6 percent of revenue during the 2006 first-quarter and 15 percent this year.

NutriSystem shares rose at one point $6.92 in after-hours trading yesterday to $65.16. The earnings were released after the market closed. In regular Nasdaq trading, NutriSystem gained $1.43 to $58.24.

Hagan is among the investors in Philadelphia Media Holdings L.L.C., which owns The Inquirer, the Philadelphia Daily News and Brian Tierney, chief executive of Philadelphia Media Holdings and publisher of the newspapers, is on NutriSystem's board.