This is a pretty common and recurring "hot" issue on the FML so there should be some references in the archives, as well. Brewer's yeast contains chromium which lowers blood glucose levels. It's often used to "regulate" blood glucose levels for diabetics... the opposite of insulinoma (hypoglycemia). Lowering blood glucose is the very LAST thing you want to do to a ferret with insulinoma. The word "regulate" in the common description of brewer's yeast has been the source of confusion on using this as a supplement for insulinoma. In this case "regulate" means "to keep from rising" NOT "stabilize". For ferrets WITHOUT insulinoma, it's a source of vitamins, amino acids, minerals... Brewer's yeast is one of the holistic world's wonder supplements and DOES have some GREAT benefits. An excellent description of it can be found at: http://www.findarticles.com/cf_dls/g2603/0002/2603000229/p1/article.jhtml But, the single side effect of lowering blood glucose makes it unsuitable for ferrets with insulinoma or humans with hypoglycemia. And yes, the Marshall Farms guarantee states that you must feed your ferret Marshall's food for the first year to comply with the warranty. I've never seen a ferret under age 1 with insulinoma (yet). During this age range, Brewer's Yeast is a good supplement. Personally, (this is only my opinion) I wouldn't be overly concerned with a ferret's primary food containing Brewer's Yeast until insulinoma is diagnosed. At that point, I would slowly change the ferret's primary diet to a high animal protein food without Brewer's Yeast. During the change (not opinion) hopefully less than two months, close attention should be given to glucose levels (weekly testing) with regard to the amount of medication (pred) the ferret is on. The pred dosage may take longer to adjust for these ferrets as the reduction of chromium in their diet is also counter-affecting the pred at a varying rate. Not all ferrets will be so drastically affected. This is stated simply because it COULD drastically affect the one ferret you happen to have... and I prefer to err on the side of safety in these cases. Debi Christy Ferrets First Foster Home Practical & easy training, care, & maintenance articles available at http://www.geocities.com/ferretsfirst/ [Posted in FML issue 3607]