- Someone’s chronotype has to do with when they tend to be awake or asleep.
- One area of research interest is how chronotype relates to food intake and other health outcomes.
- One study in women found that night owls had higher body-fat percentages, may be more likely to choose less nutritious food, and be at a higher risk for obesity.
Patterns of being awake or asleep may make a difference when it comes to metabolic health. A study recently published in Frontiers explored how chronotype related to factors like diet, when participants ate, and body composition.
Chronotype, as explained in the study, has to do with preferences of when to be asleep or awake in a 24-hour timeframe.
The research included over 250 women and found that those who tended to be “night owls” consumed more food in the evenings and had higher percentages of body fat.
Evening-type participants were also more likely to have blood sugar troubles and worse lipid (blood fat) profiles. The results also suggest that evening-type participants were more likely to make poorer food choices and be at a higher risk for obesity.
This research included 287 European and Pacific New Zealand women, who were already part of a cross-sectional study called PRedictors linking Obesity and the gut MIcrobiome (PROMISE) study.
In the current research, participants were between 18 and 45 years old and had either a body mass index (BMI) in the healthy range or one that indicated obesity. Researchers excluded participants based on factors like pregnancy or taking medications that could impact appetite.
Participants provided blood samples, answered questions about their chronotype, sleep, and work. Researchers also had data on body composition and 5 days’ worth of estimated food records. Participants wore accelerometers, which allowed researchers to look at activity level and sleep.
The study authors divided the participants into three basic categories:
- evening types, commonly referred to as “night owls”
- morning types, commonly referred to as “larks”
- intermediate.
A little over half of participants fell into this intermediate category, and researchers ended up combining the morning and intermediate groups. Participants in the evening type group were more likely to be of Pacific descent.
This group also had higher BMI, hip and waist circumference, visceral fat percentages, and android fat percentages. Android fat is fat in the upper body.
The evening type group also ate a slightly larger amount of carbohydrates each day and had larger average energy intake. The morning and intermediate type group had higher median intakes of certain vitamins, but also of alcohol and caffeine.
Researchers further looked at when participants consumed foods, and chronotype did appear to affect results.
For example, evening types had higher energy intake and ate more carbohydrates, fat, and protein in the late evening and early night, while these values were higher for the morning and intermediate groups in the late night and early morning window.
After adjustment, fat and protein intake remained higher for the evening type group in the late evening and early night timeframe.
Next, researchers looked at how body composition played into things, which it did. For example, participants with a higher body fat percentage and who were also evening types had lower energy consumption and ate less protein, fat, and carbohydrates in the late night and early morning and had higher energy intake and ate more carbohydrates and fat in the late evening and early night.
Overall, the researchers concluded that being an evening type “was associated with lower energy, carbohydrate and protein intake in the late night/early morning window, but only for the high [body fat percentage] group, which was reversed in the late evening/early night (with also higher fat intake).”
Researchers also found that having later sleep times correlated with some worse biomarkers, like higher insulin levels and triglycerides. Also, having a higher energy intake in the evening was linked to biomarkers like higher hemoglobin A1C, which is indicative of prediabetes or type 2 diabetes risk.
Overall, the results suggest some poorer outcomes for those in the evening-type chronotype group. For example, the lower intake of micronutrients could indicate a lack of intake of fruits and vegetables. Some findings also indicate that evening-types could be at a higher risk for obesity.
Speaking to Medical News Today, Sura Alqaisi, MD, an endocrinologist in the Department of Internal Medicine at UTMB, who was not involved int his study, noted the following regarding discussing the findings:
“Meal timing, in addition to total caloric intake, may play an important role in body fat distribution and metabolic health. The observation that evening chronotypes also had higher triglycerides, insulin, HbA1c, and leptin levels, along with lower HDL cholesterol, further strengthens this association.”
Alex Dimitriu, MD, double board-certified in Psychiatry and Sleep Medicine and founder of Menlo Park Psychiatry & Sleep Medicine, likewise not involved in this study, also noted that it “confirms a lot of what we have been hearing. Indeed, late evening types tend to eat less healthy foods after sunset, have a shorter period of fasting during the night, and also have a higher BMI and body fat percentage than people who go to bed earlier.”
This study focused on women of specific ethnicities, so the results cannot be generalized to other populations. Additionally, most participants who were evening types were Pacific ethnicity and scored higher on the deprivation index, so it is possible that this group had less access to healthy food.
Furthermore, much of the data was self-reported by participants, which may leave room for error. The researchers also suggest that inaccuracies in dietary data may be more likely among evening types.
The researchers also encourage looking at chronotype as something influenced by multiple components, including work and culture.
Finally, it is worth noting that this study is observational, so it cannot prove that being a night owl causes the health concerns that researchers observed.
Longer-term studies would help to verify the current findings going forward.
This study, despite its limitations, seems to indicate some possible health risks associated with being a night owl. It also indicates the need for more research. The authors suggest that future research can help with figuring out “personalized health interventions.”
Mir Ali, MD, a bariatric surgeon, bariatric medicine specialist and medical director of MemorialCare Surgical Weight Loss Center at Orange Coast Medical Center in Fountain Valley, CA, who was not involved in this research, noted that:
“The clinical implication is that there may be a benefit to certain people in adjusting their eating time, which can help reduce body fat. I emphasize to my patients that reducing carbohydrate and sugar intake, especially at night, can help reduce weight. Emphasizing proteins and non-starchy vegetables in the diet is the best approach.”
Alquaisi further pointed out that, “from an endocrinology perspective, this study suggests that chronotype should be considered as part of nutritional assessment, particularly in patients with obesity, prediabetes, type 2 diabetes, or other metabolic syndrome.”
“Rather than focusing exclusively on what patients eat, we should also consider when they eat. Overall, this study supports a more personalized approach to nutrition, where dietary recommendations are tailored not only to caloric intake restriction but also to an individual’s circadian,” she advised.
