When people think about intermittent fasting, the focus is usually on how many hours they should fast.
But research increasingly suggests another question may also be important:
How late in the day do we eat?
Our metabolism changes throughout the day
The human body follows a natural 24-hour rhythm.
This rhythm influences sleep and wakefulness, but also hormones, insulin sensitivity, digestion and the way the body processes food.
As a result, eating the same meal earlier or later in the day may not produce exactly the same metabolic response.
Earlier eating appears to have advantages
Research comparing different time-restricted eating schedules suggests that earlier eating may be more favorable for metabolic health than eating later in the day.
In recent analyses, earlier eating schedules were associated with better results for body weight and some measures of glucose and insulin regulation than later schedules.
Importantly, this suggests that the benefits of time-restricted eating may depend not only on how long the eating window lasts, but also on where that window falls during the day.
Does that mean everyone should stop eating at 5 PM?
No.
Some studies define an early eating window as finishing food intake before approximately 5 PM, and experimental studies have tested even earlier schedules.
But this does not mean that 5 PM is a scientifically established cut-off for everyone.
Daily schedules, sleep times, physical activity and individual health all differ.
Research has not established one universal time when everyone should stop eating.
What about eating before bedtime?
The evidence supports avoiding a habit of pushing a large proportion of daily food intake into the late part of the day.
However, we cannot yet say that everyone needs exactly two, three or four hours without food before sleep.
For healthy aging, the emerging message is simpler: regularly eating earlier rather than very late may be more important than following a rigid fasting rule.
