In one lab study, 36 healthy adults spent two weeks on one of three sleep schedules. One group slept five hours a night on weekdays and caught up at the weekend. They still gained weight, and their bodies handled sugar worse: lower insulin sensitivity, meaning the body responds less well to insulin, the hormone that moves sugar out of the blood. The weekend didn't undo the week. Evidence: decent
It's one small study, in a lab. Treat it as a warning, not a verdict.
The long lie-in also pushes your body clock later, so Sunday night gets harder. Evidence: decent What pays the debt is enough sleep on ordinary nights. For adults the floor is seven hours, most nights. Evidence: solid
Same theme: The rhythm
The rhythm
Same wake-up time, every day
Pick a wake-up time and keep it, weekends within an hour. Bad night or not.
no timeEvidence: decent
The rhythm
The tracker isn't the doctor
For one week, don't open the sleep score in the morning. Judge the night by how you feel mid-morning.
no timeEvidence: worth trying