Researchers looked at eating habits of over 7,000 Brazilian teenagers and found that those who eat later in the evening tend to consume more calories and make less healthy food choices, leading to weight gain. The study discovered that teenagers who eat most of their daily calories after 8 PM are more likely to be overweight. The findings suggest that when teenagers eat—not just what they eat—matters for maintaining a healthy weight. This research adds to growing evidence that our body’s internal clock affects how we gain or lose weight.

The Quick Take

  • What they studied: Whether the time of day teenagers eat affects their weight and how much food they consume
  • Who participated: 7,377 teenagers between ages 10-19 from Brazil who kept food diaries for two days as part of a national household survey conducted in 2008-2009
  • Key finding: Teenagers who ate their meals spread out over longer periods and those who ate most calories after 8 PM were more likely to be overweight. Teens with a longer nighttime fasting period (not eating for longer at night) actually had lower chances of being overweight.
  • What it means for you: If you’re a teenager or parent of one, paying attention to when meals happen—especially avoiding large meals late at night—might help prevent weight gain. However, this is one study and more research is needed to confirm these patterns apply everywhere.

The Research Details

This was a cross-sectional study, which means researchers looked at a large group of people at one point in time rather than following them over years. Scientists used information from a Brazilian government survey that tracked what families ate during two days in 2008-2009. Teenagers recorded everything they ate and drank, and researchers calculated when they ate their first meal, last meal, how long their eating period lasted, and how long they went without food at night. They also figured out what time of day the teenager had consumed half their daily calories. The researchers then compared these eating timing patterns to each teenager’s weight status using a special measurement called BMI-for-age, which accounts for the fact that teenagers are still growing.

Understanding meal timing is important because it’s something people can actually change, unlike genetics. If eating at certain times really does affect weight, teenagers and families could adjust their schedules to help prevent obesity. This approach is different from just counting calories—it focuses on the body’s natural rhythms and how they influence metabolism.

This study used real-world data from a large, nationally representative survey, which is a strength. However, because it’s cross-sectional, we can only see that late eating and weight gain happen together—we can’t prove that late eating causes weight gain. The data is from 2008-2009, so eating patterns may have changed since then. The study didn’t account for all possible factors that affect weight, like physical activity or sleep patterns, which could influence the results.

What the Results Show

Teenagers whose meals were spread out over the longest periods had a 20% higher chance of being overweight compared to those with shorter eating windows. Teenagers who consumed more than one-third of their daily calories after 8 PM had a 30% higher chance of being overweight. Interestingly, teenagers who had a medium-length nighttime fasting period (the time between their last meal and first meal the next day) actually had a 30% lower chance of being overweight. Teenagers who ate later in the day and had longer eating periods consumed significantly more total calories—sometimes hundreds of calories more per day. These patterns held true even after researchers accounted for other factors like age and gender.

The study found that later timing of the last meal and a later ‘caloric midpoint’ (the time when half the day’s calories had been eaten) were both linked to eating more total calories. Teenagers with later eating patterns also tended to make less healthy food choices overall. The associations were consistent across different age groups within the adolescent range studied.

This research supports earlier studies in adults showing that eating later in the day is connected to weight gain and metabolic problems. However, there has been limited research specifically on teenagers until now. The findings align with the concept of ‘chrononutrition’—the idea that when you eat matters as much as what you eat. Some previous research suggested that eating later disrupts the body’s natural rhythms and may lead to overeating, and this study provides evidence that this pattern may start in the teenage years.

Because this study only looked at two days of eating for each teenager, it may not represent their typical eating patterns. The data is from 2008-2009, so it’s over 15 years old and eating habits have likely changed. The study couldn’t prove that late eating causes weight gain—only that they occur together. Important factors like how much exercise teenagers got, how much they slept, or stress levels weren’t measured. The study was done in Brazil, so results might be different in other countries with different food cultures and schedules.

The Bottom Line

Teenagers and families may benefit from trying to eat meals at consistent times, with most calories consumed earlier in the day and avoiding large meals close to bedtime. This is a moderate-confidence recommendation based on this one study. It’s not a guarantee for weight loss, but it’s a reasonable habit that aligns with how our bodies naturally work. Pairing this with other healthy habits like balanced nutrition and physical activity is important.

Teenagers concerned about their weight, parents trying to help their kids maintain healthy weight, and anyone interested in preventing obesity should pay attention to these findings. This is especially relevant for teenagers who naturally tend to eat late or have irregular meal schedules. People with eating disorders or specific medical conditions should consult healthcare providers before making changes. This research is less relevant for very young children or adults, though similar patterns may apply.

Changes in eating timing won’t produce overnight results. It typically takes 4-8 weeks of consistent meal timing changes to notice differences in hunger patterns and energy levels. Weight changes usually become noticeable after 8-12 weeks of sustained habit changes, though this varies by individual.

Want to Apply This Research?

  • Log the time of your first meal, last meal, and when you eat your largest meal for one week. Track your weight weekly at the same time of day. Note any changes in hunger levels or energy throughout the day.
  • Set a specific cutoff time for eating (for example, no food after 8 PM) and track how many days you stick to it. Gradually shift your largest meal earlier in the day if you currently eat it in the evening. Use app reminders to eat breakfast within one hour of waking up.
  • Create a weekly chart showing meal times and weight. After 4 weeks, review patterns to see if earlier eating times correlate with weight stability or loss. Adjust meal times gradually if needed and continue tracking for at least 8-12 weeks to see meaningful changes.

This research suggests an association between late eating and weight gain in teenagers but does not prove that late eating directly causes weight gain. Individual results vary based on many factors including genetics, activity level, sleep, and overall diet quality. Teenagers with concerns about their weight or eating patterns should consult with a healthcare provider or registered dietitian before making significant dietary changes. This study was conducted in Brazil and may not apply equally to all populations. Parents should not use meal timing restrictions as a sole strategy for weight management in teenagers, as this requires a comprehensive approach including balanced nutrition and physical activity.