Like we announced on the more general Inside AdSense blog a couple weeks ago, we have extended our category filtering beta to English-language ads on the AdSense network, which we are happy to announce includes ads that appear in AdSense for feeds.
To have these settings take effect for your feeds, from Ad Review Center, make sure you select a Client-ID that starts with ca-feed-pub. Note that this allows you to select different categories for your feed than for your site, but also means you will need to select filters for both your feed and your site in order for filters to be applied to both these content types.
To see whether category filtering has been enabled for your location, sign in and visit the Ad Review Center, located under the 'AdSense Setup' tab. We're working on expanding this beta to additional languages and countries, and will be sure to announce any updates here on the blog. If you'd like to learn more about category filtering, please visit our Help Center.