For many generations, going to bed early and waking up early were considered key to a healthy lifestyle, and any deviation from this rule was often seen as harmful. However, scientists have discovered that being a “morning lark”—someone who wakes up early and starts the day with energy—or a “night owl”—someone who naturally goes to bed late and wakes up later—is much more than just a lifestyle choice. This pattern reflects the body’s natural preferences for sleep-wake cycles over a 24-hour period.
Nevertheless, recent research suggests that the “owl” habit may have its own metabolic downsides. The findings were published in the journal Frontiers in Nutrition.
Eating also serves as a signal for the body’s internal biological clock, and meal timing can influence metabolism. In a recent study, researchers examined whether a person’s chronotype is linked to eating habits, body composition, and overall metabolic health.
In a study conducted among a group of healthy women living in Auckland, New Zealand, it was found that “owls” consumed less energy and fewer nutrient-rich foods than women with a “morning” chronotype. Higher calorie intake in the evening was associated with a greater percentage of body fat and a higher risk of obesity.
Since most “owls” eat little in the morning and consume most of their food late in the evening, they tend to have a higher body mass index (BMI) and body fat percentage compared to “larks.”
Research shows that chronotype influences not only sleep timing but also our eating habits. While most studies focus on the total amount of food consumed, they pay less attention to the timing of calorie and nutrient intake, even though both the type and timing of meals can vary by chronotype.
People with an “evening chronotype” are more likely to eat later in the day, make less healthy food choices, and overall have poorer eating habits. They also tend to have a higher body mass index (BMI). However, BMI alone cannot distinguish between muscle mass and fat tissue. This is especially relevant in New Zealand, where women of Pacific Islander descent generally have larger body frames and more muscle mass than women of European descent.
In this study, researchers went beyond BMI. The team used the Munich Chronotype Questionnaire (MCTQ) to determine the chronotypes of 130 New Zealand women of Pacific Islander descent and 157 New Zealand women of European descent, aged 18 to 45. Based on their sleep-wake patterns, participants were classified as morning, intermediate, or evening types. Women who typically went to bed at 11:00 PM and woke up at 8:00 AM were categorized as intermediate types.
Participants then recorded everything they ate and drank over five non-consecutive days—three weekdays and two weekend days. Later, dietitians interviewed each participant to verify portion sizes and ensure the accuracy of the food records.
Instead of relying solely on body weight, researchers used dual-energy X-ray absorptiometry (DXA), a type of X-ray scan, to measure the amount of body fat in the women and where it was stored, including in the abdomen and hips. They also measured biomarkers in the blood, including blood sugar, cholesterol, and hormones related to fat tissue.
People with an evening chronotype had worse outcomes in nearly all the health indicators measured by researchers compared to those with morning and intermediate types. They had a higher average BMI and more fat tissue overall, with a higher android-to-gynoid ratio, indicating more weight around the abdomen rather than the hips—a pattern known to increase the risk of health problems. They ate less healthy food, consumed less fiber, and were deficient in essential vitamins and minerals.
Blood analysis showed that people with an evening chronotype had higher levels of insulin and triglycerides, as well as lower levels of protective HDL cholesterol. Additionally, they had elevated levels of leptin, a hormone linked to body fat storage, and lower levels of ghrelin, a hormone that signals hunger, compared to other chronotypes.
The results suggest that although all chronotype groups consumed roughly the same amount of calories and macronutrients, women with an evening chronotype showed less favorable metabolic biomarker profiles, fat tissue composition, and nutrient content in the body.
The authors argue that further research is needed on the link between chrono-nutrition and obesity, especially in ethnically diverse populations. This will help scientists better understand the true impact of chronotype and ultimately develop personalized wellness programs.
About the Author
