Researchers studied 820 Spanish teenagers to see if their natural sleep schedule affects how much junk food they eat. They found that teens who naturally stay up late eat about 2-3 more servings of ultra-processed foods per week than teens who naturally wake up early. Ultra-processed foods are snacks and meals loaded with added sugars, unhealthy fats, and chemicals. This connection held true even after accounting for other factors like exercise and family background. The findings suggest that a person’s body clock might influence their food choices, which could help doctors and parents create better strategies to help teenagers eat healthier.

The Quick Take

  • What they studied: Whether teenagers who naturally prefer staying up late eat more junk food than those who naturally wake up early
  • Who participated: 820 teenagers aged 12-17 years old living in Murcia, Spain, representing a mix of the general teenage population
  • Key finding: Evening-type teenagers ate about 34.7 servings of ultra-processed foods per week, compared to 31.9 servings for morning-type teenagers—a difference of nearly 3 servings per week
  • What it means for you: If you’re naturally a night owl, you might want to pay extra attention to your food choices, as your body’s natural rhythm may make you more likely to reach for junk food. This doesn’t mean you’re doomed to eat unhealthy—just that you might need different strategies than early risers.

The Research Details

This was a cross-sectional study, which means researchers looked at a group of teenagers at one point in time rather than following them over months or years. The researchers asked 820 Spanish teenagers about their natural sleep preferences using a special questionnaire called the Morningness/Eveningness Scale for Children. This scale asks questions to figure out whether someone is naturally a morning person, evening person, or somewhere in between. The teenagers also filled out a detailed food frequency questionnaire where they reported what they typically eat, which helped researchers calculate how much ultra-processed food they consume each week. Ultra-processed foods were identified using the NOVA system, which is an international classification that groups foods by how much processing they’ve gone through.

The researchers then used statistical analysis to compare ultra-processed food consumption across the three chronotype groups (morning, intermediate, and evening types). They adjusted their analysis to account for other factors that might affect eating habits, like age, gender, family income, physical activity level, and body weight. This adjustment helps ensure that any differences they found were actually related to chronotype and not just due to other lifestyle differences.

Understanding whether your natural sleep schedule influences your food choices is important because it could lead to personalized health strategies. If evening-type teenagers naturally tend to eat more junk food, doctors and parents could develop specific approaches to help them make better choices that work with their body’s natural rhythm rather than against it. This research approach is valuable because it looks at real-world eating patterns in actual teenagers rather than in a controlled lab setting.

This study has several strengths: it used a large sample of 820 teenagers, it measured both chronotype and food intake using validated tools (meaning these tools have been tested and proven reliable), and it adjusted for multiple factors that could influence results. However, because it’s a cross-sectional study, it only shows a connection between chronotype and junk food eating—it doesn’t prove that being an evening type causes someone to eat more junk food. The study was conducted in Spain, so results may not apply exactly the same way to teenagers in other countries with different food cultures and lifestyles.

What the Results Show

The main finding was clear: teenagers with an evening chronotype (night owls) consumed significantly more ultra-processed foods than those with a morning chronotype (early birds). Evening-type teenagers ate an average of 34.7 servings of ultra-processed foods per week, while morning-type teenagers ate 31.9 servings per week—a difference of 2.8 servings. This difference was statistically significant, meaning it’s unlikely to have happened by chance.

Intermediate-type teenagers (those without a strong preference for morning or evening) fell in the middle, eating 33.4 servings per week. They also ate significantly more junk food than morning types, though not quite as much as evening types. These differences remained even after researchers accounted for factors like age, gender, family income, physical activity, and body weight, suggesting that chronotype itself plays a role in food choices.

To put this in perspective, if a serving of ultra-processed food is something like a candy bar, soda, or packaged snack, the difference means evening-type teenagers might eat about 2-3 more of these items per week compared to morning types. Over a year, this could add up to hundreds of extra servings of junk food.

The study confirmed that the relationship between chronotype and junk food consumption held true across different groups of teenagers, regardless of their socioeconomic background or activity level. This suggests the connection is fairly consistent and not just limited to certain types of teenagers. The findings also support previous research showing that evening-type people tend to have less healthy eating patterns overall.

This research builds on earlier studies that found evening-type people tend to eat more junk food and have worse overall diet quality. Previous research also showed that evening types are more likely to eat late at night and skip breakfast, both habits linked to unhealthy eating. This Spanish study adds to that evidence by specifically measuring ultra-processed food consumption in teenagers and showing the effect is real even when controlling for other lifestyle factors.

This study has several important limitations to keep in mind. First, it only shows a connection between chronotype and junk food eating—it doesn’t prove that being an evening type causes someone to eat more junk food. There could be other factors not measured in the study that explain both the chronotype and eating habits. Second, the study only included teenagers from one region of Spain, so the results might not apply the same way to teenagers in other countries or cultures. Third, the study relied on teenagers reporting their own food intake, which can be inaccurate—people sometimes forget what they ate or underestimate portion sizes. Finally, because this was a snapshot in time rather than following teenagers over months or years, we can’t know if these patterns stay the same or change over time.

The Bottom Line

If you’re a teenager who naturally prefers staying up late, pay extra attention to your food choices and try to include more whole foods like fruits, vegetables, and whole grains. Consider planning healthy snacks in advance for late-night eating, since evening types may be more prone to late-night snacking. Parents and healthcare providers might consider developing personalized nutrition advice based on whether a teenager is a morning or evening type. However, these recommendations are based on one study, so more research is needed before making major changes. (Confidence level: Moderate—the findings are interesting but not yet strong enough to be considered definitive medical advice.)

Teenagers who identify as evening types or night owls should pay attention to these findings, as should their parents and healthcare providers. Teachers and school nutritionists might also find this useful when developing school lunch programs or nutrition education. However, this doesn’t mean morning-type teenagers can ignore their diet—they still need to make healthy choices, just perhaps with less targeted intervention. This research is less relevant to very young children or adults, though similar patterns may apply.

If an evening-type teenager makes changes to eat less junk food and more whole foods, they might notice improvements in energy levels and how they feel within 2-4 weeks. More significant changes in weight, skin clarity, or athletic performance could take 2-3 months. However, the most important thing is making sustainable changes that work with your natural rhythm rather than expecting overnight transformation.

Want to Apply This Research?

  • Track ultra-processed food servings daily, noting the time of day consumed. Evening-type users should specifically monitor late-night snacking patterns to identify when they’re most vulnerable to junk food choices.
  • Set up alerts during typical high-risk times (evening/night hours for evening types) to remind users to choose whole foods. Create a ‘healthy evening snack’ list in the app with pre-approved options that evening-type users can grab instead of ultra-processed alternatives.
  • Weekly review of ultra-processed food intake trends by time of day. Compare weekly averages over 4-week periods to track progress. Set personalized reduction goals (e.g., decrease evening-type junk food servings by 10% every two weeks) rather than aiming for elimination.

This research shows an association between being a night owl and eating more junk food in teenagers, but it does not prove that one causes the other. These findings are from one study in Spain and may not apply equally to all teenagers worldwide. This information is for educational purposes and should not replace personalized medical advice from a doctor or registered dietitian. If you have concerns about your teenager’s diet or eating habits, please consult with a healthcare professional who can provide individualized guidance based on their complete health picture.