Wall Street is doubting Kraft Heinz after the food giant wrote down the value of its iconic Kraft and Oscar Mayer brands.

Kraft reported a goodwill impairment charge of $15.4 billion in the fourth quarter, resulting in a net loss of $12.61 billion. Last year, Oscar Mayer's sales totaled $5.44 billion and the Kraft brand's sales totaled $5 billion, according to market research firm Euromonitor International. The two brands represent about 15 percent to 20 percent of the company's portfolio, at least in the U.S., Piper Jaffray analyst Michael Lavery said.

These brands are two of the company's most important brands, worrying the Street that if Kraft can't manage these brands, it may not be able to compete in today's competitive grocery landscape.

Packaged food companies across the board are feeling pressure as consumers abandon iconic brands and opt for private label products or new upstart brands. People are also increasingly shopping the perimeters of stores, meaning they're buying more fresh foods and less packaged foods that make up the bulk of companies like Kraft's portfolio.

Since Heinz acquired Kraft in 2015, the company has relentlessly slashed costs. Some have worried this cost-cutting came at the expense of much needed investments to compete for today's consumer. The write downs reported Thursday intensified those fears.

"We believe these impairments validate fears that [Kraft] may have been more focused on costs than building brand equity, and even if management now has 'seen the light', we are now concerned that its brands lack the equity to drive pricing power needed to compete and drive growth in a sustainable way," Lavery wrote in a note to clients Friday.

Kraft Heinz is a product of 3G Capital, a Brazilian investment firm known for slashing costs. So is Anheuser-Bush InBev, a megabrewer that has found its main Budweiser and Bud Light brands losing market share as consumers drink more craft beer.

Based on the dismal fourth-quarter results and 2019 forecast Kraft gave Thursday, it's now "more than fair to ask if any fundamental value" has been created since the Kraft Heinz merger, J.P. Morgan analyst Ken Goldman wrote in a note to clients Friday. Between Kraft and ABI's struggles, Goldman said it's "reasonable to question the entire 3G strategy."

"Investors for years have asked if 3G's extreme belt-tightening model ultimately would result in brand equity erosion," Goldman wrote. "We think the answer arguably came yesterday in the form of a $15B (!) intangible asset write-down for the Kraft and Oscar Mayer brands."

Kraft also revealed Thursday it's the subject of a Securities and Exchange Commission investigation. The company received a subpoena in October related to its accounting policies, procedures and internal controls related to procurement.

Shares tanked 27 percent in trading Friday morning, hitting a 52-week low of $35. Even before taking Friday's losses into consideration, the company's stock was down more than 28 percent over the past month, although shares were making gains since the start of this year.