To address this question Dr. Joelle Oosterman gave rats either rodent chow or chow plus either saturated fat or a sugar solution. One group was allowed to consume the diets freely whereas the other groups were only allowed to eat either the fat or sugar during their inactive period. They found that rats consuming all of their sugar solution in the inactive period gained more weight than rats consuming all their sugar solution during the active period, even though their total caloric intake was the same. They also gained more weight than rats consuming the saturated fat solely during the inactive period. The greater body weight gain in rats consuming sugar in the inactive period was associated with less heat production.
This research suggests that there are differences in the impact sugar drinking can have on body weight gain, depending on when in the day it is consumed. Dr. Oosterman commented, "In today's society where snacks containing saturated fat and beverages containing lots of sugar are readily available to people, it is important to understand the impact these food components have on energy balance. Although there is a lot of attention for the content of the food people consume, little attention is been given to the best or worst timing for certain foods to be consumed."