Some of the bars and shakes have SOY in them. Soy can affect your thyroid, decreasing it's output. If your thyroid slows down, weight loss will slow down too. It is just another possibility to consider. For those with healthy thyroids it is not much of a problem, but for those who already have slow thyroids or borderline ones, it can be bad news. You might check the Thyroid board on here if you think it might apply to you.