Night owls, listen up: staying up late might be doing more than throwing off your sleep schedule. A new study suggests it could be quietly packing on belly fat, too—and food choices may be the reason.
What researchers actually studied
Scientists looked at more than 250 women who were part of a larger study on obesity and gut health.
Participants, ages 18 to 45, either had a healthy body mass index or a BMI that fell into the obesity range. Anyone pregnant or taking medications that affect appetite was excluded from the analysis.
Everyone gave blood samples, wore activity trackers, answered questions about sleep and work schedules, and logged five days of food intake.
Based on their sleep and wake preferences, researchers sorted participants into three groups: night owls, morning people known as “larks,” and an in-between group. Because more than half the women fell into the middle category, researchers combined the morning and intermediate groups for comparison with night owls.
Night owls carried more fat—and in a specific pattern
The night owl group showed higher BMI, larger waist and hip measurements, and more visceral fat, the type that wraps around internal organs and is closely tied to metabolic disease.
They also had more upper-body fat, along with higher blood sugar and triglyceride levels compared to the morning and intermediate groups.
Interestingly, the morning and intermediate group had higher “bad” cholesterol levels—so it wasn’t a simple case of one group being universally healthier across every marker.
It’s not just what you eat—it’s when
This is where the study gets interesting. Night owls consumed slightly more carbohydrates and more total calories overall.
But the real story was timing. Night owls ate more calories, fat, protein, and carbs late in the evening and early in the night. Morning types, by contrast, ate more during the late-night and early-morning hours.
Even after adjusting for other factors, night owls still ate more fat and protein in that late evening window.
Among participants with higher body fat percentages, being a night owl meant eating less in the early morning hours but significantly more in the late evening—especially more fat.
The blood sugar connection
Later sleep times were linked to higher insulin and triglyceride levels. Eating more in the evening was also tied to higher hemoglobin A1C, a marker used to flag prediabetes and type 2 diabetes risk.
An endocrinologist who was not involved in the study but reviewed the findings noted that meal timing, not just total calories, may influence where the body stores fat and how it handles blood sugar. Higher triglycerides, insulin, and A1C levels alongside lower “good” cholesterol in night owls strengthen that connection.
A sleep medicine specialist, also not involved in the research, said the findings echo a pattern seen elsewhere: people who stay up later tend to eat less healthy food after dark, get a shorter overnight fasting window, and often carry higher body fat than earlier risers.
Where the sleep piece fits in
This research adds to a growing pile of evidence that sleep timing and quality are deeply tied to metabolic health, not just energy levels. For people struggling to shift their body clock earlier or simply trying to get better-quality rest regardless of chronotype, sleep support products like 4GreatSleep* are designed to help address the sleep side of that equation. Better rest alone won’t undo poor food timing, but improving sleep quality may make it easier to stick to healthier evening habits*.
The fine print worth knowing
This research only looked at women, and most participants were of specific ethnic backgrounds, so the findings can’t be applied broadly to everyone.
Most night owls in the study were of Pacific ethnicity and scored higher on a deprivation index, raising the possibility that limited access to healthy food, not chronotype alone, played a role in the results.
Food logs were also self-reported, and researchers noted that inaccuracies may be more common among night owls specifically.
And this is an observational study — it shows a link, not proof that staying up late causes weight gain.
Bottom line
Being a night owl isn’t a life sentence for a bigger waistline, but this study adds real weight to something doctors have suspected for years: when you eat may matter almost as much as what you eat.
If late-night snacking has become part of your routine, the fix probably isn’t a stricter diet — it’s shifting the clock. Eating earlier, tightening your overnight eating window, and getting sleep on a more consistent schedule may do more for your metabolism than cutting calories alone ever could.
For now, the takeaway for night owls is simple: your bedtime habits might be showing up on the scale — and on your labs — decades before you’d expect.
FTC Disclosure: Keith and Kathryn, the authors of this article, are co-founders of 4VitaHealth LLC and may receive compensation from products or services mentioned, including 4GreatSleep.
*FDA Disclaimer: Statements regarding dietary supplements or sleep support products have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure, or prevent any disease.
The information in this article is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always talk with a qualified health care provider, endocrinologist, or sleep specialist about concerns related to weight, metabolic health, blood sugar, or sleep patterns before making changes to your diet, sleep schedule, or supplement routine.
