Margen
Monday, day 1: thirty-six healthy adults check into a sleep laboratory at the University of Colorado. They are split into three groups. One will sleep nine hours a night; another, five; the third, five from Monday to Friday and then as much as it likes at the weekend.
Friday, day 5: both five-hour groups are already snacking after dinner. That is the window through which the calories that later show up on the scales get in.
Saturday and Sunday: the weekend group is allowed to sleep as much as it wants. They sleep 1.1 hours more than usual — nowhere near what they owe. Nobody spends the day in bed: the body will not take that much sleep at once.
Monday, day 8: back to five hours. And here comes the part nobody expected: insulin sensitivity in the group that had caught up fell further still than in the group that never slept in at the weekend. Both groups had put on about a kilo and a half.
The study was signed by Christopher Depner in the journal Current Biology in 2019, and it dismantles a very comfortable idea: sleep debt is not a current account you settle on Sunday morning.
This week, if you can only move one hour, move Tuesday's: go to bed an hour earlier on weekdays and leave Sunday's alarm exactly where it was.