New York (CNN Business) Oprah Winfrey famously proclaimed "I love bread!" in a Weight Watchers commercial three years ago. But carbs aren't cutting it for the company anymore.

WW WTW Shares of— Weight Watchers' new name — closed down 34% on Wednesday after the company shocked Wall Street with poor earnings and sales. The stock rebounded a bit Thursday morning, rising 8%.

CEO Mindy Grossman attributed the problem to the keto diet, a popular eating regimen that makes bread and other carbs taboo. She said during a call with analysts Tuesday that keto is "becoming a cultural mean," and she even called it a "keto surge."

Wall Street is clearly nervous, too.

JPMorgan analyst Christina Brathwaite downgraded the stock to "underperform" last week and slashed her price target. One of the reasons? She was worried about competition from rival weight-loss service Diet Doctor, which is a proponent of keto.

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