On Monday, PepsiCo announced that CEO Indra Nooyi will step down in October. Nooyi, who has led the company for 12 years, will be replaced by current president Ramon Laguarta.

Her departure comes at a time when women make up just 4.8 percent of Fortune 500 CEOs, and just 25 women hold the CEO spot at S&P 500 companies, according to research group Catalyst. When Nooyi officially steps down, that number will decrease to 24 until Kathryn Warden steps into her role as the CEO of Northrop Grumman in January 2019.

Her exit also comes on the heels of several other departures by female CEOs, including Campbell Soup CEO Denise Morrison, Hewlett Packard CEO Meg Whitman and Mondelez CEO Irene Rosenfeld.

Lisa Mann, CEO and founder of Think Marketing, tells CNBC's "Power Lunch" that Nooyi's departure speaks volumes about the growing concern around corporate America's ability to keep female leaders.

"Companies should be embracing their VPs and SVPs who are women and nurturing them to be leaders in business," says Mann, who once worked at PepsiCo under Nooyi's leadership. She emphasizes that 80 percent of consumer purchasing power is held by women.

Nooyi, who joined PepsiCo in 1994 as head of strategy, has been open about her belief that companies need to do a better job of diversifying their leadership by hiring more women and people of color. But she points out that the drop-off in women leaders is not only attributed to the professional pain points women experience throughout a career, but the personal ones as well.

"We get a lot of women in at the entry-level positions. As you get to middle management, women rise to those positions, and then that's the childbearing years," she told the Freakonomics radio show in February. "And when they have children, it's difficult to balance having children, your career, your marriage, and be a high-potential out-performer who's going to grow in the company."