“…Selection can be profoundly influenced by factors typically considered hedonic or cognitive rather than physiological in nature, such as the textural composition of the nutrients offered (9), the previous experience of the rats with macronutrients (16), and the social transmission of information about the diets (1,3). It has been suggested that animals may not be able to "discover" a needed diet ingredient if the choice of available foods is large (5). Here, we provide experimental support for this by showing that a seemingly trivial factor from a physiological perspective, i.e., the number of sources of CHO or fat available, was sufficient to reduce the selection of protein so much that many animals failed to thrive.…”