How can a late bedtime affect my weight?

Researchers at Northwestern University examined the effects of sleep timing on diet and body mass index (BMI) and found that late bedtimes and late mealtimes can lead to less healthful diets and to weight gain.

A group of 52 adults -- 25 women and 27 men -- spent seven days keeping food logs and having their sleep and waking activity measured by a wrist sensor. The researchers divided participants into two categories:
  • “Normal sleepers” reached the midpoint of their night’s sleep before 5:30 a.m. These sleepers were asleep by shortly after midnight and woke around 8 a.m. Among the study group, 56% were normal sleepers.
  • “Late sleepers” reached the midpoint of their nightly sleep after 5:30 a.m. They went to sleep in the middle of the night, well after midnight, and woke in the mid- to late morning. Among the study group, 44% were late sleepers.
Researchers tracked the eating habits of these two types of sleepers through the information provided to them from the participants’ food logs:
  • Normal sleepers ate breakfast by 9 a.m., lunch at 1 p.m. and dinner at 7 p.m., on average. These sleepers reported being finished with eating for the day by 8:30 p.m.
  • Late sleepers reported eating their first meal of the day at about noon. They ate again in the middle of the afternoon, and did not eat dinner until after 8 p.m. Late sleepers did not finish their eating for the day until 10 p.m., on average.
What were the consequences for sleeping later and eating later? Researchers found that late sleepers suffered across the board, in terms of the quality and quantity of both their daily sleep and eating:
  • Late sleepers slept less overall than normal sleepers -- an average of more than an hour less per night.
  • Late sleepers consumed more calories at dinnertime than normal sleepers. They also consumed significantly more calories after 8 p.m.
  • Late sleepers had poorer-quality diets than normal sleepers -- they ate more fast food, drank more sugar-laden soda and ate fewer vegetables.
These habits of late sleepers were all found to be associated with a higher body mass index. Among these habits, eating after 8 p.m. was the strongest predictor of a higher BMI. What does this mean? It’s not just what you eat, but when you eat, that can affect your ability to lose weight. And your sleep habits can have a significant influence on the timing of your eating, as well as on how much you eat.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.