Tl;dr: During the day, when potential DNA damage from UV light is higher than at night, the circadian rhythms in your skin upregulate expression of enzymes which protect & repair DNA. They also downregulate proliferation because the last thing you want is for a harmful DNA mutation to be rapidly spread. All of this thanks to a robust circadian rhythm.
Time-Restricted Feeding Shifts the Skin Circadian Clock and Alters UVB-Induced DNA Damage (Wang et al., 2017)
In general, LIGHT entrains the central circadian clock and FOOD entrains peripheral clocks. That's why we try to get a big breakfast and go outdoors in the morning (or mimic this as closely as possible).
And from the aforementioned blog post, there is a bona fide circadian rhythm in skin, too. Well it appears this one, similar to other peripheral tissues, is regulated in part by FOOD but is also influenced by LIGHT.
Restricted feeding windows (eg, 14/10 or 16/8) or other intermittent fasting regimens may depend on the timing of the actual feeding window, with earlier windows faring better from a circadian perspective.
1) big early breakfast at sunrise, medium lunch whenevs, early light dinner prior to sunset...
2) food intake restricted to the active phase (daytime for humans; nighttime for mice).
In this study, researchers fed animals at various intervals throughout the day, roughly analogous to humans eating most of their food at sunrise, sunset, or all day long.
The orange line is ad lib, and not surprisingly, they weigh the most.
This might be a stretch, but compare the blue line (breakfast-eaters) with the green line (dinner-eaters): they all gain weight but the breakfast-eaters weighed more in the beginning of the study and less than (or at least equal to) the dinner group by the end! Not sure if this is an artefact, but it is in agreement with actual human studies on this...
The other part of the study was a more difficult nut to crack.
Mice are supposed to eat during the active phase (night for them, day for us), when there's not supposed to be a lot of UV light.
When the researchers zapped 'em with UVB light at this time, circadian mismatch and way more sunburn then when they were zapped during the daytime.
Alternatively, when mice were forced to eat during their rest phase, which happens to be during the day for mice, their protective mechanisms should've suppressed UVB-induced skin damage but didn't because they were in a state of circadian mismatch [because they were being forced to eat at the wrong time]. Meal timing plays into circadian entrainment.
The only “win-win” was the group that was allowed to eat during the active phase and got zapped during the daytime.
In other words, the group with species-appropriate proper circadian entrainment.
In general, LIGHT entrains the central circadian clock and FOOD entrains peripheral ones. That's why we try to get a big breakfast and go outdoors in the morning (or mimic this as closely as possible)...
Translation: big early breakfast at sunrise, medium lunch whenevs, early(ish) light(ish) dinner prior to sunset... food intake restricted to the active phase.
That's all I got. For now 👊🏿