Dave Feldman's claim is that ldl cholesterol reflects the previous three day's of eating. If it changes that quickly, you can't even be certain your cholesterol results have much to do with your period on Atkins, since you' been off it for a couple of days. Even that one day might not count, if you'd been malabsorbing fat while on the diet, and that caused the diarrhea, it might not be the fat that was digested that raised your ldl, a low carb diet in which you malabsorb enough of the fat is going to effectively be a lower fat diet.