Night Owl Eating Habits May Increase Obesity Risk

Your sleeping pattern—whether you're a night owl or an early bird—could be having a significant impact on your metabolic health.

In a new study of nearly 300 women, led by researchers from Griffith University, Australia, and Massey University, New Zealand, scientists found that night owls were more likely to eat foods high in calories, carbohydrates, and fats late at night. Being a night owl was also associated with higher blood sugar and lipid levels, as well as having a higher body fat percentage, despite having a similar daily calorie intake to the other groups.

"People seem to think that excess food intake and body weight are a simple case of eating too much, and therefore simple solutions are reducing food intake or increasing exercise. However, as dietitians, we know that it is not so simple," study author Prof. Rozanne Kruger, professor of nutrition and dietetics at Griffith University, told Technology Networks. "There are many other influences that play a role, for example our patterns of food intake (when we eat), the types of food we eat, and how much we eat at different times."

The link between sleep timing and metabolic health

While a simple "calories in, calories out" approach to food and energy expenditure is followed by many people attempting weight loss, Kruger explained that, in reality, there are other factors that can greatly affect a person's weight.

"In my career, I found success when helping people maintain the same amount of food, but making healthier choices and spreading it across the day, balancing nutrients and energy," Kruger said. "Therefore, when we conducted a large study among healthy women with different body composition profiles, I wanted to explore the diet in-depth, looking at the nutritional quality but also the timing of eating during the day. This set the scene to also investigate chronotypes and their associations with metabolic health among these women."

A total of 287 European and Pacific New Zealand women were included in the study, all otherwise healthy and aged between 18–45 years. For each woman, body fat percentage, android-to-gynoid fat percentage ratio, and body mass index were measured, with blood samples also collected to assess metabolic markers. In addition, each participant was asked to complete a five-day estimated food record to measure food intake, and a questionnaire assessing sleep habits.

"We defined chronotype using the Munich Chronotype Questionnaire, alongside data from sleep watches and sleep diaries, which is an intricate process," Kruger explained. "The two extremes at either end of the 24-hour day cycle are termed 'morning chronotypes' and 'evening chronotypes.'"

"A person who never goes to sleep before midnight and then sleeps late into the mid- or late morning is likely an evening type/night owl. In contrast, a person that cannot stay awake after 8:00 or 9:00 P.M. (early evening), and wakes up during the very early morning hours, is likely a morning type/early bird. These are the extreme chronotypes. There are also intermediate chronotypes which operate between these two extremes," Kruger added.

In the study population, 34% of the women were classified as being evening types. Only 12% fit the criteria for being a morning type.

Watching your weight? Try watching the clock

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Overall, the early birds and night owls had similar calorie intakes across the study period. The main difference in food intake was seen in the timing of their eating; night owls consumed less food between the hours of 3:00–10:00 A.M., but comparatively more food between 8:00 P.M.–3:00 A.M. The opposite was true for the early birds, who would often eat an early breakfast and rarely eat at night.

Although overall calorie intake was similar between both groups, this difference in timing can have very distinct effects on the body, Kruger explained.

"A person’s chronotype influences much more than just their sleep patterns; it also influences the timing of diurnal (day/night) activity preferences and thus variation of physiological functions and behavior," she said.

"During the daytime, the body uses insulin efficiently to process glucose, meaning we use most of our energy for activity and body processes, e.g., breaking down fat, rather than storing it. The opposite happens when we are at rest, because our tissues and organs are also in a ‘rest phase’. If this cycle is changed and meals are eaten in the rest phase, this circadian disruption will result in poor insulin release and processing of carbohydrates and fats, leading to storage and ultimately higher body fat and poor metabolic health."

This effect can be seen in the study; being a night owl was associated with having a greater body fat percentage and holding more belly fat. They also tended to have higher blood sugar levels, poorer lipid profiles, and less favorable indicators of glucose regulation than their peers. Such a metabolic profile may increase the risk for diseases such as type 2 diabetes or cardiovascular disease.

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"Evening types are often sleeping late in the morning and skipping their breakfast, which results in eating all their other meals later in the day. People do not eat less because they slept late; they tend to just redistribute their energy and macronutrient intake of the skipped meals to later in the day, often during the night when they stay awake later—and if they wake up late they tend to go to bed later, continuing this cycle," Kruger said.

"Evening types therefore still eat the same amount of food/energy, but in a shorter timeframe, and often larger meals in the rest phase, leading to storage in the body. All energy from the food we consume must be used; otherwise, it will be stored as fat. Hence, eating smaller amounts at one eating occasion is good practice. Another [good practice] is to eat less energy-dense food at night, for example, eating fruit versus chocolate-chip cookies, ice cream, or fatty takeaway food."

Exploring how sleep preferences impact individual metabolism

The study has several notable strengths. While previous research has tended to focus on people who are overweight or obese, this study included a broader sample of healthy premenopausal women. The use of multiple body composition measures and metabolic biomarkers is also a strength.

However, Kruger does highlight some limitations of the work: "Misreporting of dietary data may have been more prevalent among evening types due to their irregular eating patterns and behaviors. Furthermore, this study was not designed to include equal chronotype groups; hence we found overall lower [numbers of] morning types and higher intermediate and evening types across the whole sample, and not an equal distribution among ethnicities."

"This age group (younger, pre-menopausal) was more likely to be intermediate or late chronotypes (older age groups often are morning types). Therefore, we merged morning and intermediate types into one group for data analysis, wanting to maintain the larger evening type group independently as they were more metabolically implicated in the literature due to circadian misalignment. This meant, however, that we could not explore the intermediate types independently," she added.

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To avoid adverse eating behaviors, Kruger recommends avoiding excessively long sleeps during daytime hours, as this can lead to later bedtimes and introduce a cycle of eating and sleeping late.

"A simple principle is to never eat more than we need at any time, as the excess will be stored as body fat. It is good eating practice to distribute our food intake across various eating occasions during the day, and not to stretch it into the night," Kruger said. "Aim for eating dinner around 6:00-7:00 P.M., but no later than 8:00 P.M., and avoid eating food within two hours before going to sleep to allow processing of the food rather than storage. At night, try not to snack mindlessly on energy-dense foods such as chips, chocolates, ice cream, or takeaways while being distracted watching a movie, social media, or playing games—it leads to overeating. Try to eat breakfast within two hours of waking up and therefore aim to never skip a meal. Eat smaller amounts of food and make nutritious choices."

In terms of future research, Kruger hopes to further explore this aspect of "chrono-nutrition" and study how it links to obesity outcomes in other populations, "particularly in ethnically diverse populations, different genders, those living in different socio-economic environments or working night shifts to better distinguish the independent effects that chronotype may have."

Reference: van der Merwe C, Richter-Cottle M, Breier BH, Douwes J, Münch M, Kruger R. Chronotype and associations with dietary intake, meal timing, body composition, and metabolic biomarkers. Front Nutr. 2026;13. doi: 10.3389/fnut.2026.1862060

About the interviewee:

Professor Rozanne Kruger is the discipline lead for nutrition and dietetics in the School of Health Science and Social Work at Griffith University in Australia. She also has an honorary research fellow position in the School of Sport, Exercise, and Nutrition at Massey University in Auckland, New Zealand. Kruger was instrumental in developing the MSc (Nutrition and Dietetics) programme at Massey University in 2012, establishing a programme with a strong research focus, delivering competent graduates entering the dietetics profession.

Kruger is a registered dietitian (RD(SA); NZRD; APD) and nutrition researcher and has worked extensively with vulnerable groups in both clinical and community settings, conducting trans-disciplinary cross-sectional and intervention studies including dietary intake, physical activity, metabolic health, and body composition assessment. She has led many clinical nutrition studies and interventions in New Zealand, showing that clinical dietetic practice is key to the treatment of disease and improved patient outcomes. She continues to significantly contribute to the dietetics profession. She mentors staff, has graduated 13 cohorts of dietitians, and supervised 6 honours, 57 MSc, and 11 PhD students to completion. She has published articles in nationally and internationally accredited journals and presented at conferences worldwide.

Kruger is passionate about developing novel dietary assessment strategies, exploring dietary patterns, dietary diversity, eating behaviour, and chronotype nutrition, and using food-based approaches as solutions. She enjoys developing new and interesting research approaches and training strategies.