"Migration is slowing because people have migrated," McGuinness said. "Now you have to drive more people into the category."
Greek yogurt now accounts for 46 percent of dollar sales of yogurt, according to Nielsen. In the year ended in November 2010 only one out of every 10 dollars was spent on Greek yogurt.
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Despite the slowing growth, James Russo, senior vice president of global consumer insights at Nielsen, said in a phone interview he doesn't "think we've hit the ceiling on Greek yogurt," as the category still has strong growth.
"We think the category should double if not triple," McGuinness said.