A large study of nearly 6,000 adults in the United Kingdom found that when you eat during the day affects your weight. Eating more calories in the evening was connected to higher chances of being overweight, while eating more in the morning was linked to lower weight. The study also discovered that ultra-processed foods (like packaged snacks, fast food, and sugary drinks) were especially problematic when eaten in the evening. The connection between evening junk food and weight problems was stronger than at other times of day, suggesting that the timing of what we eat might be just as important as what we eat.

The Quick Take

  • What they studied: Whether the time of day people eat, and the types of food they eat at different times, affects their weight and body shape
  • Who participated: 5,749 adults aged 19 to 64 years old living in the United Kingdom (England, Wales, Scotland, and Northern Ireland). Researchers looked at their food diaries from 2008 to 2019 to see what they ate and when.
  • Key finding: Eating more calories in the evening was linked to a 21% higher chance of being overweight. Eating ultra-processed foods in the evening increased the odds of obesity by 45%. Morning eating, by contrast, was associated with lower weight.
  • What it means for you: If you’re trying to manage your weight, when you eat might matter as much as what you eat. Eating more substantial meals earlier in the day and limiting processed foods in the evening may help. However, this study shows a connection, not proof that changing meal timing will cause weight loss.

The Research Details

Researchers analyzed information from a large national survey where people in the UK kept detailed food diaries for four days. They looked at data collected between 2008 and 2019 from nearly 6,000 adults. The researchers divided the day into three eating periods: morning (5 AM to 11 AM), midday (11 AM to 5 PM), and evening (5 PM to 5 AM the next day). They measured how much energy (calories) people ate at each time and how much of that came from ultra-processed foods—items like packaged snacks, fast food, sugary drinks, and processed meats.

The researchers then looked at whether the timing and type of food people ate was connected to their weight status. They measured weight in three ways: using BMI (a height-to-weight ratio), checking if people were overweight or obese, and measuring belly fat around the waist. They used statistical methods to account for other factors that affect weight, like exercise, sleep, smoking, and social class.

This approach allowed researchers to see patterns in real eating habits across a large, representative group of people, though it couldn’t prove that eating at certain times directly causes weight gain.

Understanding when people eat and what they eat at different times helps us understand real-world eating patterns and weight problems. This study used actual food diaries from thousands of people rather than asking them to remember what they ate, making the information more reliable. By looking at a whole country’s eating habits over many years, the findings may apply to many people.

This study has several strengths: it included a large number of people, used actual food diaries rather than memory, and adjusted for many other factors that affect weight. However, because it’s a cross-sectional study (a snapshot in time), it shows connections between eating patterns and weight but cannot prove that changing meal timing causes weight loss. The study also relied on people accurately recording their food intake, which can be challenging. The findings are from the UK, so they may not apply equally to all populations worldwide.

What the Results Show

The study found clear patterns linking meal timing to weight. Adults who ate the largest percentage of their daily calories in the morning had a 19% lower chance of being overweight compared to those who ate less in the morning. In contrast, those who ate the most calories in the evening had a 21% higher chance of being overweight.

Ultra-processed foods showed even stronger connections to weight problems. When people ate the highest amounts of ultra-processed foods in the morning, they had a 26% higher chance of obesity. At midday, the highest ultra-processed food intake was linked to a 25% higher obesity risk. In the evening, this jumped dramatically to a 45% higher obesity risk. This means that eating junk food in the evening was associated with nearly double the obesity risk compared to eating it in the morning.

For belly fat specifically, eating ultra-processed foods in the evening was particularly concerning. A 10% increase in evening ultra-processed food calories was linked to a 12% higher chance of having excess belly fat. This pattern was less pronounced for morning and midday eating.

The study also found that even smaller increases in ultra-processed food consumption mattered. For every 10% increase in ultra-processed food calories eaten at midday or evening, people had about 11% and 10% higher odds of being overweight, respectively. This suggests that even modest increases in processed food, especially later in the day, may add up to weight problems over time.

Previous research has suggested that meal timing affects metabolism and weight, but most studies focused on breakfast skipping or intermittent fasting. This study adds important information by looking at the full day’s eating pattern and specifically examining ultra-processed foods. The finding that evening eating is more strongly linked to weight gain aligns with some earlier research suggesting our bodies may handle calories differently at different times of day. However, the particularly strong connection between evening ultra-processed food and obesity is a newer insight that builds on previous work.

This study shows connections between eating patterns and weight, but it cannot prove that changing when you eat will cause weight loss. Because it’s a snapshot of eating habits at one point in time, we can’t know if people who eat more in the evening gained weight because of that habit, or if people who already had weight problems changed their eating patterns. The study relied on people accurately recording their food intake for four days, which can be difficult and may not represent their typical eating. Additionally, the study was conducted in the UK, so results may differ in other countries with different food cultures and lifestyles. Finally, the researchers adjusted for many factors, but other unmeasured factors could influence the results.

The Bottom Line

Based on this research, consider eating a more substantial breakfast and lunch, and keeping dinner lighter and less processed. Limit ultra-processed foods throughout the day, but especially in the evening. These changes may help with weight management, though individual results will vary. Confidence level: Moderate. This study shows strong patterns, but changing eating habits requires sustained effort and works best combined with regular physical activity and adequate sleep.

Anyone concerned about weight management, overweight individuals, and people with excess belly fat should pay attention to these findings. People trying to prevent weight gain as they age may find this information particularly useful. However, these findings may not apply equally to people with certain medical conditions, those taking medications that affect weight, or people with different cultural eating patterns. If you have specific health concerns, discuss meal timing and food choices with your doctor or registered dietitian.

Changes to eating patterns typically take 4-8 weeks to show measurable effects on weight. Some people may notice improved energy levels and digestion within 1-2 weeks. Significant weight changes usually take 3-6 months of consistent habit changes. Remember that weight is just one measure of health, and other improvements like better energy and improved blood sugar control may happen first.

Want to Apply This Research?

  • Log the time of each meal or snack along with whether it’s a processed or whole food. Track your weight weekly and note any patterns between evening processed food intake and weight changes over 4-week periods.
  • Set a specific goal like ‘Replace one evening processed snack with a whole food option three times per week’ or ‘Eat 30% of daily calories before noon.’ Use app reminders for meal prep or healthier evening snack options.
  • Create a simple chart showing daily ultra-processed food intake by time of day and weekly weight trends. Review monthly to identify patterns and adjust. Track energy levels and digestion quality alongside weight to see broader health impacts.

This study shows associations between eating patterns and weight but does not prove that changing meal timing will cause weight loss. Individual results vary based on genetics, overall calorie intake, physical activity, sleep, and many other factors. Before making significant changes to your eating patterns, especially if you have health conditions, take medications, or have a history of eating disorders, consult with your doctor or a registered dietitian. This research is informational and should not replace personalized medical advice.