For today’s edition of Dear Mark, I’m handling just one question. I originally planned to answer more reader questions, but it turned into a complex answer that really made me dig deeper into something – butyric acid – I’d assumed was completely benign. I still do, mind you, for the most part. The position has just become more nuanced. Anyway, the question is from a reader who’s just seen a study that seems to implicate butyric acid, the primary short chain fatty acid that resistant starch-eating gut bacteria produce, in colon cancer. Was my ringing endorsement of resistant starch a mistake after all?