The Franklin, Tenn., company's stock also was downgraded by SunTrust Robinson Humphrey to hold from buy.
Tivity said CEO Donato Tramuto departed the company. He joined the board in 2013 and was named CEO in fall 2015.
Robert Greczyn, a current director, will serve as interim CEO until a new permanent chief is named.
Kevin G. Wills, independent chairman, said during a conference call with analysts that "after much thought and discussion, the board determined that it would be in the best interest of all stakeholders to transition to a new CEO."
In addition, Keira Krausz, who heads the nutrition business, resigned on Tuesday. Chief Operating Officer Tommy Lewis will head the business on an interim basis.
SunTrust Robinson Humphrey analyst David MacDonald said in a note to clients that he cut his price target to $15 from $25 due to "continued deterioration in the nutrition business, some margin pressure in healthcare, management departures and disappointing 2020 guidance."
Tivity Health, whose brands include Nutrisystem, South Beach Diet and Silver Sneakers, reported a fourth-quarter loss of $323.1 million, or $6.69 a share, compared with earnings of $28.5 million, or 67 cents a share, a year ago. Adjusted earnings came to 40 cents a share, missing FactSet's consensus forecast of 55 cents a share.
Revenue totaled $272.8 million, up from $153 million a year ago, but fell short of FactSet's call for revenue of $275.2 million.
Looking ahead, Tivity said it expects first-quarter revenue to range from $335 million to $350 million, and $1.24 billion to $1.29 billion for the year. Wall Street was looking for revenue to come in at $369.8 million for the first quarter, and $1.34 billion for the year.
"While we see the conceptual attractiveness of the combined nutrition/fitnessmodel, execution has been elusive, visibility in the nutrition business is limitedand the company's debt load bears watching," SunTrust's MacDonald said.
Tivity Health acquired Nutrisystem last year for about $1.3 billion and Wills said that "admittedly, the nutrition business has not worked out as well as planned since the completion of the acquisition in March of 2019."
"We have made some good progress in the past 10 months, particularly in our approach to digital marketing, and we're seeing some promising results in certain key growth metrics for our Nutrisystem brand," Wills said.