Although a large number of experiments have been conducted in humans, the majority are based on animal models. Results, and how they should be interpreted, depend on the choice of several parameters made by the investigators regarding study designs and protocols. These include species, strains, sex, and age of animals, but also diet composition and study duration (Sidransky 1990; van Raaij et al. 1983; Westerterp 1999). These experimental data are discussed along with analysis of their results.