So he's both a hands-on cook and an activist! From the article:
Mr. Kass, 29, forged a close bond with the Obamas while cooking for them and their children for about two years before they moved to Washington and has golfed with the president on Martha’s Vineyard. Behind the scenes, he attends briefings on child nutrition and health, has vetted nonprofits as potential partners for White House food initiatives and regularly peppers senior staff about policy matters.
Sam Kass appears regularly in the blog ObamaFoodorama.