Nutritional products giant Herbalife reported better-than-expected quarterly earnings on Monday amid strong demand for its products and raised its forecast for 2013, signaling to its high-profile detractors that the company is confident about the months ahead.

Herbalife reported net income for the second quarter was $143.2 million, or $1.34 per share, compared with $132.0 million, or $1.09 per share, a year earlier.

Adjusted earnings per share was $1.41. Analysts anticipated earnings of $1.18, according to Thomson Reuters I/B/E/S.

The Los Angeles-based company also raised its 2013 forecast for adjusted earnings per share to a range of $4.83 to $4.95 from $4.60 to $4.80 previously.

Net sales rose 18 percent to $1.2 billion, driven by strong demand for weight-loss and nutrition products worldwide, the company said.

Herbalife has spent much of 2013 caught in the crosshairs of activist investors Carl Icahn and Bill Ackman, who have waged a public battle over whether the company will fail.

Ackman, who runs hedge fund Pershing Square Capital Management, said in December that he had a $1 billion bet against the "multi-level marketer," whose weight-loss products are sold through a network of independent individuals.

Ackman has called the Los Angeles-based company "a pyramid scheme" and predicted that its shares will eventually be worthless, while Icahn publicly supported the company and put two of his representatives on Herbalife's board of directors.

Herbalife CEO Michael Johnson has said Ackerman's allegations are "bogus."

Herbalife shares were up 5 percent to $64.22 in extended trading, up from a close of $60.57.