Why do some people jump out of bed before sunrise while others feel wide awake late at night?
Scientists say this difference is not simply a habit. It is linked to the body’s natural internal clock, called the circadian rhythm, which helps control sleep, hunger, body temperature, hormones, and energy levels over each 24-hour day.
People who naturally wake early are often called morning types or early birds. People who naturally stay up late are often called evening types or night owls.
A new study suggests that these natural sleep patterns may also affect eating habits, body fat, and overall metabolic health. The research was published in Frontiers in Nutrition.
Researchers wanted to understand whether the body’s natural sleep timing could influence health beyond sleep itself. Earlier studies had suggested that people who stay up late often choose less healthy foods and eat later in the day.
However, many of those studies mainly looked at body weight. Body weight alone cannot show how much of a person’s body is fat and how much is muscle. The new study took a closer look.
The research included 287 healthy women between 18 and 45 years of age living in Auckland, New Zealand. The participants included both Pacific and European women.
Scientists used the Munich Chronotype Questionnaire to determine whether each participant was a morning, intermediate, or evening type based on her usual sleep schedule.
The women then recorded everything they ate and drank over five separate days, including weekdays and weekends. Dietitians checked these records to improve accuracy.
The researchers also used DXA scans, which provide a detailed picture of body fat and where it is stored. Blood samples were collected to measure blood sugar, cholesterol, triglycerides, insulin, and hormones involved in appetite.
The results showed clear differences. Night owls usually ate very little during the morning and consumed much more of their food later in the day. They also ate fewer foods rich in vitamins, minerals, and fiber. Even though total calories and major nutrients were similar across the groups, the timing and quality of food were different.
Women who stayed up later generally had higher body fat, higher body mass index, and more fat around the waist.
Fat stored around the stomach is considered more harmful because it is linked to heart disease, type 2 diabetes, and other long-term health problems. Blood tests also showed higher insulin and triglyceride levels, lower HDL cholesterol, higher leptin, and lower ghrelin, suggesting less healthy metabolism.
Scientists believe meal timing may help explain these differences. The body’s internal clock prepares the body to digest and use food at different times of the day. Eating large meals late at night may not match these natural rhythms.
The findings do not prove that being a night owl directly causes obesity or poor health. The study only found a relationship between chronotype and health measurements. Exercise, stress, work schedules, genetics, and sleep quality may also influence the results. Because the study involved only healthy women from one city, more research is needed in men, older adults, and other populations.
Overall, the study suggests that paying attention to both when we sleep and when we eat may become an important part of future health advice. Personalized nutrition plans based on a person’s natural body clock may eventually improve long-term health.
The findings appear to be carefully collected because the researchers used detailed diet records, body scans, and blood tests instead of relying only on body weight.
However, larger studies following people for many years are still needed before firm conclusions can be made. The research provides strong evidence that our body clock may influence much more than sleep and deserves further investigation.
If you care about sleep health, please read studies about foods that help people sleep better, and Keto diet could improve cognitive function in people with sleep loss.
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