Maintaining a healthy weight may depend not only on food choices but also on meal timing. A study published in the International Journal of Behavioral Nutrition and Physical Activity found that two habits are linked to a lower body mass index (BMI) over time: extending the overnight fasting period and eating breakfast early. The research was led by the Barcelona Institute for Global Health (ISGlobal), a centre supported by the “la Caixa” Foundation.
The findings are based on data from more than 7,000 adults between the ages of 40-65 who are part of the GCAT | Genomes for Life cohort, led by the Germans Trias i Pujol Research Institute (IGTP). In 2018, participants provided details about their height, weight, meal timing, lifestyle habits, and socioeconomic background through questionnaires.
Five years later, in 2023, more than 3,000 of these individuals returned for follow-up assessments. Researchers recorded updated measurements and collected new survey data, allowing them to track changes and identify patterns over time.
Early Eating and Longer Fasting Linked to Lower BMI
“Our results, in line with other recent studies, suggest that extending the overnight fast could help maintain a healthy weight if accompanied by an early dinner and an early breakfast. We think this may be because eating earlier in the day is more in line with circadian rhythms and allows for better calorie burning and appetite regulation, which can help maintain a healthy weight. However, it is too soon to draw definitive conclusions, so recommendations will have to wait for more robust evidence,” explains Luciana Pons-Muzzo, researcher at ISGlobal at the time of the study and currently at IESE Business School.
Gender Differences and Lifestyle Patterns
When researchers compared results by gender, they found notable differences. Women generally had lower BMI, followed the Mediterranean diet more closely, and were less likely to drink alcohol. At the same time, they reported poorer mental health and were more often responsible for household or family supervision.
Using a method called ‘cluster analysis’, the team grouped participants with similar characteristics. One small group of men stood out. These individuals typically ate their first meal after 14:00 and fasted for about 17 hours. Compared to others, they were more likely to smoke and drink alcohol, less physically active, and less likely to follow the Mediterranean diet. They also tended to have lower levels of education and higher rates of unemployment. Researchers did not observe a similar pattern among women.
Intermittent Fasting and Breakfast Skipping
“There are different ways of practising what is known as ‘intermittent fasting’ and our study relates to one of them, which is overnight fasting. What we observed in a subgroup of men who do intermittent fasting by skipping breakfast is that this practice has no effect on body weight. Other intervention studies in participants with obesity have shown that this tactic is no more effective than reducing calorie intake in reducing body weight in the long term,” says Camille Lassale, ISGlobal researcher and senior co-author of the study.
Chrononutrition and the Body’s Internal Clock
“Our research is part of an emerging field of research known as ‘chrononutrition’, which focuses not only on analysing what we eat, but also the times of day and the number of times we eat,” says Anna Palomar-Cros, researcher at ISGlobal at the time of the study and currently at IDIAP Jordi Gol. “At the basis of this research is the knowledge that unusual food intake patterns can conflict with the circadian system, the set of internal clocks that regulate the cycles of night and day and the physiological processes that must accompany them,” she adds.
Earlier Meals Linked to Broader Health Benefits
This study builds on earlier ISGlobal research in chrononutrition. Previous findings have shown that eating dinner and breakfast earlier in the day is associated with a lower risk of cardiovascular disease and type 2 diabetes, reinforcing the idea that meal timing plays a meaningful role in long-term health.
