But, by the evening, they were also eating more sugars and fats.
By Saturday and Sunday, they not only ate less healthily but they also indulged in irregular meal times, often, very late-night eating.
They were more prone to snacking on sugar and fat-rich items.
This, the study's authors claimed, put them at higher risk of obesity and metabolic disturbances in the future.
In addition, they also suffered poorer sleep and were less physically active.
"Evening types are more prone to live against their internal biological time," lead author Mirkka Maukonen told the New York Times. "Our society is pretty much structured to suit morning types better."
However, she added that adapting is possible.
"[Our body clocks are] influenced half by genes and half by environment. Also, awareness of one's own chronotype may encourage paying more attention to overall healthier lifestyle choices.
"Also, awareness of one's own chronotype may encourage paying more attention to overall healthier lifestyle choices."