Even America's busiest CEOs make time for good reads. But it's not exactly leisure reading--many business leaders see books as crucial for helping them run their companies. Call it brain fuel or creative inspiration.

Here are five must-reads as recommended by the CEOs of some of America's fastest-growing private companies.

1.  Good to Great by Jim Collins --Kevin Lustig, Scientist.com, No. 9 on the Inc. 5000

"I found that I absolutely resonated with almost everything in there," says Lustig, the CEO and founder of the Solana Beach, California-based online health care marketplace. It's a fairly quick read that analyzes successful companies and their CEOs.

The author emphasizes that truly great companies do not have "flashy CEOs who go around beating their chest" like they are celebrities, Lustig says. "The best CEOs are the ones that realize that it's the employees that do all the heavy lifting and that they're there to build the culture." 

2. Tribal Leadership by Dave Logan and John King --Justin Quinn, Natural Force, No. 431 on the Inc. 5000 

Quinn says this book taught him that leadership is the one skill that can't be outsourced. Quinn's co-founder, Joe Rakoski, says that Tribal Leadership is now required reading for all new team members at the Jacksonville, Florida-based fitness supplement company. "The more leadership you can foster throughout all arms of your business, the easier it will be to continue to scale your businesses' growth," Rakoski says.

"And you better get damn good at empowering others if you hope to navigate fast growth," Quinn adds.

3. The Lean Startup by Eric Ries --Patrick Vihtelic, Home Chef, No. 3 on the Inc. 5000

Eric Ries's seminal business book inspired the Chicago-based meal kit company founder to make the leap into entrepreneurship. Vihtelic says he read it shortly after it came out in 2011, "as I was more seriously considering making a transition out of finance and into the entrepreneurial world." In 2013, he started his company with those thrifty principles in mind. In 2017, his company booked nearly $255 million in revenue, a 60,166 percent jump since 2014.

4. What Does It All Mean by Thomas Nagel --David Barnett, PopSockets, No. 2 on the Inc. 5000 

This is no business book. The author is frank in his attempt to analyze philosophical theories. The first sentence of the book reads, "This book is a brief introduction to philosophy for people who don't know the first thing about the subject."

For Barnett, a former philosophy teacher, suggesting this book makes sense: "It touches quickly on some central problems of philosophy," the founder of the Boulder, Colorado-based cellphone-grip maker says. "It will get the mind going."

5. Endurance: Shackleton's Incredible Voyage by Alfred Lansing --Mark Gallagher, GForce Life Sciences, No. 8 on the Inc. 5000

"It's about overcoming tremendous odds," says the founder of the Chicago-based biotech staffing firm. Gallagher says the story resonated with his own personal experience with struggling. GForce is the founder's second business. He got pushed out of his first staffing firm, which he co-founded with his cousin in 1987.