Carey started the new Jenny program in late July following the birth of her twins, Monroe Cannon and Moroccan Scott Cannon, in April.
"I'm just here as a catalyst. Ideally, this will help create awareness -- my goal is to at least make a difference," said Carey, who has sold more than 200 million albums to date.
"As an artist, I use my voice to entertain. But, today I want to use my voice to draw attention to a serious matter. Two-thirds of the country is placing themselves at risk for heart disease and diabetes. Largely, that is due to unhealthy eating patterns and lack of physical activity," Carey said Wednesday.
"I obtained a greater understanding of this when I was pregnant with my twins and dealing with my own health issues. That's why I feel so strongly about working with Jenny and the American Heart Association to help Americans get serious about their health as it pertains to these issues which are so important."
Other recent Jenny Craig spokeswomen have been Carrie Fisher and Queen Latifah.