DUBLIN, April 30 (Reuters) - Shares in nutrition supplement maker Glanbia GL9.I jumped 10% on Wednesday after analysts pointed to a "better than feared" first quarter performance that allowed the Irish group to maintain its full year earnings guidance.

Glanbia shares plummeted to a near two-year low in February when it forecast that earnings could fall by up to 11% this year due to a prolonged rise in the cost of whey - a key ingredient in the protein powders and shakes popular with gym goers.

It said on Wednesday that while whey prices remain elevated, they had come off their peak and it had bought enough to see it through to the fourth quarter and retain its full year margin expectations for its performance nutrition business.

While first quarter group revenue grew by 7.2% year-on-year, performance nutrition fell 6.6% with its large Optimum Nutrition protein powder brand down 3.1% due to lower sales in U.S. fitness clubs that Glanbia had flagged in advance.

Analysts at Davy Stockbrokers had expected Optimum Nutrition sales to fall by 14% in the quarter and Goodbody Stockbrokers said the overall outcome was "better than feared."

The analysts were also encouraged by a 0.4% increase in U.S. consumption of Optimum Nutrition. Glanbia CEO Hugh McGuire said while he was very aware consumer confidence was falling in the U.S., protein products remain a resilient category.

Glanbia also said it had largely mitigated its exposure to tariffs through price increases and plans to sell U.S manufactured products earmarked for China into alternative markets.

Shares in the company were 9.8% higher at 0830 GMT, trimming the year-to-date loss to 16.7%. Goodbody said a fuller recovery was unlikely until sustained improvement is seen at half year.

Asked on an analyst call about activist investor Clearway Capital's call for a break up of the company, McGuire said Glanbia would listen to all shareholder proposals and that there were "no sacred cows" as it looks to continuously create value.

McGuire added that the planned sale of its underperforming U.S. weight management brand SlimFast is at the early stages.

(Reporting by Padraic Halpin;Editing by Elaine Hardcastle)

((padraic.halpin@thomsonreuters.com; +353 1 500 1504; Reuters Messaging: padraic.halpin.thomsonreuters.com@reuters.net))