If I eat cookies and subsequently brush my teeth such that there is still small amounts of cookie material stuck to my teeth, the toothpaste will not foam as well as usually, making the process less enjoyable. This effect is consistently reproducible with most (sweet) cookies but any not other foods I have tried so far. The toothpaste contains typical foaming agents, such as sodium lauryl sulfate. What could be the mechanism behind this effect?
My first take on this is that the cookies contain fat, which "consumes" the surfactants in the toothpaste (like sodium lauryl sulfate) so it does not foam up the way it normally would. You might want to see what Wikipedia says about micelles and how they interact with fats. A similar effect can be seen when washing really greasy dishes with an insufficient amount of dishwashing liquid - in which case no suds will form. In your case I don't understand why the effect would not also be observed with other fatty foods such as chocolate or popcorn.