This may be the Key Pharase

[Guest guest]

The sugar-fed rats, for example, showed the expected uptick in

core body temperature at mealtime, corresponding to their anticipation of a

bolus of calories that they would need to start burning off — a sort of

metabolic revving of the energy engines. The saccharin-fed animals, on the

other hand, showed no such rise in temperature.

http://www.time.com/time/health/article/0,8599,1711763,00.html?cnn=yes