I've read anecdotal evidence that says that real ale, though not as gassy as lager, makes you fart more.
Is there any truth to this and does it apply to ales in general or just certain types?
The actual answer has more to do with yeast content than carbonation. Unfiltered beers like real ale have much more yeast in suspension, and yeast has a tendency to make you gassy when digested. Lager in general has very little yeast due to the long, cold, aging process. I believe commercial examples are filtered as well. In general most commercial beers are filtered, or at least have had the yeast killed off somehow, which mitigates the effect. Real ale's major selling points are that it's unpasteurized and unfiltered, and is refermented in the cask...so it's basically got way more yeast and way more active yeast than other kinds of beer. And then cask ales are served from a tap at the front near the bottom...near the yeast. Basically the perfect storm of fart-induction.