Caloric consequences of sugar solutions: a failure to obtain gustatory learning.

Rats decrease total caloric intake, sometimes to the point of starvation, when sugar solutions are offered in conjunction with a daily pellet meal. This phenomenon appears to be based on a tendency to behave as if overestimating the caloric value of simple sugars. In these experiments, rats were exposed to a variety of conditions that allowed the opportunity to monitor the taste and postingestive properties of sucrose or glucose solutions. Despite these repeated opportunities to learn the true caloric value of the solutions, the rats continued to exhibit the exaggerated response. The results suggest that the gustatory receptors that have evolved to detect the normally low concentrations of sugars in the natural environment may be inherently inaccurate in response to relatively high concentrations of pure sugars. Furthermore, the rat may be contraprepared to form the quantitative gustatory associations that would be necessary to correct this error tendency.