Herbalife Nutrition plunged in early trading on Friday after Carl Icahn, the nutritional supplements maker’s biggest cheerleader, said he was selling about a quarter of his shares.

Herbalife fell 6% to $50.46 Friday morning after the billionaire investor said he would sell 11.4-million of his current 45.7-million shares in the company. He would remain its largest holder if all the shares in the offer were taken up, he noted in a regulatory filing.

"For almost six years, we have been one of Herbalife’s strongest, most loyal supporters: we stood by the company through a half-decade long short-selling campaign and we never sold a share, even after our investment doubled," he said in a statement.

Since taking his position in Herbalife in 2012, more than $7bn have been created for shareholders, he said. But his holdings had become outsized in his own Icahn Enterprises portfolio, accounting for 24% of its net asset value. It was only prudent to sell off part of his holdings, he said.

Icahn has been a public supporter of Herbalife as it battled short-seller Bill Ackman, who claimed it was a pyramid scheme. After several twists and turns, including a settlement with federal regulators, the company announced in 2017 that it was taking out a loan to buy back $600m of its shares through a tender offer. That is the vehicle Icahn used to reduce his stake.

Ackman, meanwhile, admitted defeat in the fight earlier in 2018 and sold off his position in the company.

Icahn said he continued to be supportive of Herbalife.

"We believe Herbalife’s business is stable, the short-sellers have largely exited, and the company is well-positioned for the future," he said.

With Matt Townsend