Greek yogurt is increasingly replacing traditional yogurt options like the Yoplait brand, undermining investor sentiment in the product's parent company, General Mills, which is scrambling to adjust its product offerings.

RBC Capital Markets analysts on Thursday downgraded their outlook for General Mills stock from "outperform" to "sector perform" amid reservations about the company's yogurt sales.

The move came as General Mills is set to report its second-quarter fiscal earnings Tuesday. The company posted sales and profit declines for its fiscal first quarter ended Aug. 28. Its U.S. retail sales of yogurt declined 15% during the period, compared to a year earlier, according to a securities filing.

General Mills is grappling with an onslaught of healthy-eating trends as many customers have embraced natural, organic foods.

The cereal-maker's stock (GIS) slipped 0.3% to $62.66 in mid-day trading Thursday.

"While it is conceivable that cereal growth can return to growth, the recent deterioration in yogurt has been concerning," RBC analyst David Palmer said in a research note.

Greek yogurt, viewed as a healthier option, has snapped up market share in recent years from traditional yogurt. Greek yogurt accounts for 36% of total yogurt sales, up from 1% in 2007, according to research-firm IBISWorld.

Meanwhile, overall yogurt output is slipping. U.S. production of plain and flavored yogurt fell 0.3% to 4.74 billion pounds in 2015, according to the U.S. Department of Agriculture's National Agricultural Statistics Services.

General Mills spokesperson Bridget Christenson said the company's recently introduced line of Annie's organic yogurt and premium Liberté lineup for adults will help.

Other changes include using whole milk in Yoplait Kid yogurt and increasing protein content in Yoplait Greek 100.

"The company is investing in significant innovation and renovation in yogurt to improve its U.S. yogurt performance," Christenson said in an email.

Still, competitors are swarming. The number of yogurt companies has ballooned, increasing at a 3.5% annualized pace over the last five years to a total of 96 in 2016, according to IBISWorld.

Greek yogurt competitors such as Dannon and Chobani have taken business away from General Mills. The company's U.S. yogurt revenue in the 2015-16 fiscal year was $1.34 billion, down 10.4% from 2010-11, according to IBISWorld.

One potential opportunity for the company is expansion in China, where it is launching Yoplait sales.

Follow USA TODAY reporter Nathan Bomey on Twitter @NathanBomey.