July 19, 2026, 6:46 am | Read time: 5 minutes
Sleep can indirectly affect our body fat. This is the conclusion of a new study, which underscores previous research findings. Those who are active earlier in the morning often eat more for breakfast and less in the evening. Late risers, on the other hand, tend to have habits that negatively impact metabolism, according to the study. FITBOOK has the details.
Whether someone jumps out of bed full of energy in the morning or becomes truly productive only late at night is partly genetically determined. This so-called chronotype apparently influences not only the sleep-wake cycle but also eating behavior. This has possible consequences for weight and metabolism. This is the result of a new study by researchers at Massey University in New Zealand. The study was published in the journal “Frontiers in Nutrition.”1
Evening Types Eat Later–and Weigh More
The study evaluated data from 287 healthy women between the ages of 18 and 45. The researchers determined the chronotype using the “Munich Chronotype Questionnaire” (MCTQ).
Participants kept detailed dietary records over five days. Additionally, body fat and fat distribution were measured using a DXA body scan. The researchers also analyzed various metabolic markers in the blood, including blood sugar, insulin, and blood lipid levels.
Among the participants:
- 54 percent were of the intermediate chronotype,
- 34 percent were evening types (“night owls”),
- 12 percent were morning types (“larks”).
The findings showed that evening types had an average BMI of 31.4, while morning and intermediate types together averaged 26.1. The body fat percentage, particularly abdominal fat, was also higher among the night owls.
Not the Amount of Calories, but the Timing Made the Difference
Interestingly, the total daily energy intake differed little overall (an increase of about 50 kilocalories for the late chronotypes). Although evening types consumed slightly more energy on average, the difference was relatively small. The distribution of calories throughout the day differed much more significantly.
Early risers and those with an intermediate chronotype consumed significantly more energy, as well as more protein, carbohydrates, and fat, before 10 a.m. Evening types, on the other hand, ate relatively little in the morning and shifted a significantly larger portion of their calories to after 8 p.m. This pattern was particularly pronounced among women with higher body fat percentages or more abdominal fat.
The authors calculated that evening types consumed only about nine percent of their daily energy before 10 a.m. This was compared to about 15 percent for the earlier chronotypes. After 8 p.m., however, around 23 percent of the daily energy intake was consumed by the evening types—compared to only about eleven percent for the morning and intermediate types.
Poorer Metabolic Values in Night Owls
In addition to differences in eating behavior, the researchers also found differences in various metabolic markers.
Women with an evening chronotype showed, among other things:
- higher insulin levels,
- higher HbA1c levels (a long-term marker for blood sugar),
- higher triglycerides,
- lower HDL cholesterol levels (“good” cholesterol)
These values are generally considered to indicate a less favorable metabolic profile.
Additionally, their diet was overall less nutrient-dense. The evening types consumed less fiber and lower amounts of vitamin A, vitamin E, folic acid, magnesium, potassium, calcium, and iodine.
Early, Late, or Normal? Take the Chronotype Test!
Is the Clock the Enemy of Our Sleep?
The Study Does Not Prove Causation
Despite the striking correlations, the authors urge caution in interpretation. This is a cross-sectional study. It can only show that certain sleep and eating habits are associated with higher body fat and less favorable metabolic values—not that late eating or a later chronotype causes these changes.
There are additional limitations: Only healthy women between 18 and 45 years old were studied. Moreover, the group of evening types consisted predominantly of women of Pacific origin, which could mean that ethnic and social differences influenced the results. The diet was recorded through self-reporting, which is inherently prone to error, while blood samples were taken without considering the menstrual cycle, which could affect hormone levels and appetite.
Conclusion
The study suggests that not only the amount of calories but also the timing of food intake could be related to body weight and metabolism. Early risers (larks) were more likely to have breakfast and distributed their energy intake more evenly throughout the day, while evening types (owls) consumed a larger portion of their calories late in the evening. Whether a conscious shift in meal timing actually leads to better health, however, still needs to be shown by intervention studies.