Having trouble convincing your clients to think charitably? If so, you might want to mention that a number of studies have shown that people who give to causes they believe in find that doing so feels good, really good, according to Eileen Heisman, president and CEO of the National Philanthropic Trust in Jenkintown, Pa, which manages donor-advised funds.

“The same feeling you get from an orgasm, or doing a certain kind of drug, you actually get from a certain sort of giving,” Heisman told a recent gathering at the Women Advisors Forum in Newport Beach, Calif. “I don’t usually talk about it at the podium, but since it’s only women …”

In all seriousness, Heisman urged planners to remember that certain activities that clients think will bring them happiness, often don’t. These might include making purchases or going on vacations. But giving to others and to issues they are passionate about can create a durable sense of well-being, she says.

Perhaps this is what continues to motivate Americans, who remain the most philanthropic people in the world, to keep giving at steady rates. Even in tough economic times, Heisman pointed out, Americans tend to give at consistent levels.

“Giving has been about 2% of GDP for the last 40 years,” Heisman said. U.S. philanthropists found they enjoyed giving so much last year that they gave a total of $300 billion, she added. “It’s not affected by downturns.”

And, interestingly, individuals account for 75% of those donations. “So it’s individuals,” Heisman says, “not foundations and corporations that are making most of the gifts.”