The Hungry Brain: Outsmarting the Instincts That Make Us Overeat

by Stephan Guyenet

What would normally be a harmonious performance is reduced to a disorganized cacophony. Researchers call this circadian desynchrony and hypothesize that it leads to metabolic problems and weight gain. To test this idea, Arble studied two groups of mice, both eating the same fattening diet. One group had access to food only during the twelve hours of the day when they would normally be awake and active, while the other only had access to food during the twelve hours of the day when they would normally be asleep.139 Under normal, unrestricted conditions, mice eat about two-thirds of their food during the wake cycle and one-third during the sleep cycle. In Arble’s experiment, however, they could only eat during one period or the other, leading to two circadian conditions: one in which digestive and metabolic clocks were synchronized with the master clock in the brain, and one in which they were desynchronized. Surprisingly, mice in both groups ate the same amount of food. Yet after two weeks, a striking trend began to emerge: the synchronized mice were hardly gaining weight, while the desynchronized mice were gaining fast. By the end of the six-week experiment, the desynchronized mice had gained nearly two and a half times more weight than the synchronized mice, and they tended to have more body fat as well. They were eating the same number of calories but metabolizing them differently.