David Rubenstein, co-founder and co-CEO of The Carlyle Group (CG), said market valuations are high but the private equity firm is finding opportunity in the energy and healthcare space. Rubenstein also said while the economy is pretty attractive in many areas, 'we have to worry about a slowdown at some point.' He pointed out that the U.S. tends to have recessions every 7 or 8 years, so he suspects over the next couple of years there will be some slowdown. Rubenstein explained that a recession is both good and bad for private equity. As a buyer, p/e can find more opportunities, but the companies they own could go down in value and selling them may be more difficult. A recession also can negatively impact performance. Right now, there are fewer investment opportunities for Carlyle. 'I think market valuations are high. I wish they were lower,' said Rubenstein. 'We're trying to be very restrained, we've invested less money this year than we thought we would at this point. But we don't really want to put money out the door, just because we have money to invest. We are very disciplined.' Carlyle is investing in the energy space, which is attractive as oil prices have fallen and asset prices have been reduced. Rubenstein said healthcare is another area that Carlyle finds attractive, as that sector is an increasingly important part of the U.S. economy, especially now that the Affordable Care Act is here to stay. Rubenstein spoke to TheStreet's Rhonda Schaffler at the Aspen Ideas Festival in Aspen, Colorado.