University of Utah biology professor Wayne Potts, right, and former Ph.D. student James Ruff, left, set up one of the "mouse barns" used in their new sensitive test to detect toxicity. The blue bins are desirable, sheltered territories that contain separate nesting cages. The elongated green planters are less desirable territories because mice must nest in them in the open. By having house mice compete for food and territory in mouse barns, the researchers showed that a diet of 25 percent extra sugar doubles the death rate among female mice and leaves males a quarter less able to hold onto territory and reproduce. The diet that produced these toxic effects in mice is proportional to a healthy human diet plus three cans of sweetened soda daily.