Effect of different levels of dietary fat on fat preference of mice. The effects of 10 diets differing in fat content (from 4.5 to 42% by weight) on the fat consumption of adult male mice were investigated. Diets were offered ad libitum to a group of 8 animals for two different periods of time (14 and 35 days). The most evident effect was the increase in the preference for the more concentrated diets with an increase in fat content. The results obtained are consistent with the notion that fat-rich diets are more highly favored by mice and this preference might explain the overconsumption of fat-rich diets by humans and other animals. The time course for this effect also suggests that the fat-preferring effect observed with increasing fat content of the diet was a property that was not dependent on previous exposure to fat during the pre-experimental period.