I have only read bits and pieces of one of Suzanne's books but I have read Michel Montignac's book Eat Yourself Slim.

I know that Suzanne gives a lot of credit to Schwarzbein but it sounds to me like Sommersizing (or the Schwarzbein version) has been taken directly from Montignac--eating proteins and complex carbs separately, the two levels, etc. In his book, Montignac explains how came up with the diet to deal with his own weight gain (1987), and also goes into some of the science behind it. I found it very interesting as it explains the glycemic index (how different foods affect how the quantity of glucose your body produces).