Morning people may instinctively choose a healthier diet than night owls do.
Finnish researchers tracked the diets of 1,854 men and women ages 25 to 74 and used a well-validated questionnaire to classify them as morning people or evening types.
After controlling for age, sex, education, B.M.I., smoking, sleep time and other factors, they found that total energy intake did not differ between morning and evening types.
But on weekdays, evening types ate less in the morning and tended to choose breakfast foods that were higher in sugar and lower in fiber, carbohydrates and fats, including saturated fat. By evening, the night owls were eating more sugar and fats than the morning people.
On weekends, the differences were even greater. Evening people ate significantly more sugar and fats, had more irregular mealtimes, and ate meals and snacks twice as often as morning people. The study appears in the journal Obesity.
“Evening types are more prone to live against their internal biological time,” said the lead author, Mirkka Maukonen of the Finnish National Institute for Health and Welfare. “Our society is pretty much structured to suit morning types better.”
Can night owls adapt? “It is possible,” Dr. Maukonen said, because our chronotype — our natural inclination for when we wake and sleep — “is 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.”