Keeping a healthy weight might be influenced not just by what we eat but also when we eat. A study in the International Journal of Behavioral Nutrition and Physical Activity suggests that two habits are associated with a lower body mass index (BMI): lengthening the overnight fasting period and having breakfast early. This research was led by the Barcelona Institute for Global Health (ISGlobal), supported by the “la Caixa” Foundation.
The results are based on information from over 7,000 adults aged 40 to 65, who are part of the GCAT | Genomes for Life project conducted by the Germans Trias i Pujol Research Institute (IGTP). In 2018, participants filled out questionnaires detailing their height, weight, meal timings, lifestyle, and socioeconomic status.
Five years later, in 2023, more than 3,000 participants returned for follow-ups. Researchers took updated measurements and gathered new survey responses to observe changes and identify trends over time.
Early Eating and Longer Fasting Linked to Lower BMI
“Our findings align with other recent studies and indicate that lengthening the overnight fast may help in maintaining a healthy weight, particularly if it’s paired with an early breakfast and dinner. This might be because eating earlier corresponds better with our natural circadian rhythms, enhancing calorie burning and appetite management, which could support weight maintenance. Although, I should mention, it’s still too early for definitive recommendations until more solid evidence is available,” said Luciana Pons-Muzzo, a researcher with ISGlobal during the study, now at IESE Business School.
Gender Differences and Lifestyle Patterns
When breaking down the results by gender, distinct differences emerged. Women tended to have a lower BMI, adhered more closely to the Mediterranean diet, and were less likely to consume alcohol. Conversely, they reported worse mental health and often took on household or family responsibilities.
Using ‘cluster analysis’, the researchers categorized participants with similar traits. A small group of men caught their attention. These men usually had their first meal after 2 PM and fasted for roughly 17 hours. Compared to their peers, they were more inclined to smoke, consume alcohol, engage in less physical activity, and not follow the Mediterranean diet closely. Additionally, they generally had lower educational attainments and higher unemployment rates. There was no comparable trend among women.
Intermittent Fasting and Breakfast Skipping
“There are various approaches to ‘intermittent fasting’, and our study focuses on one variant, overnight fasting. We observed that a subgroup of men practicing intermittent fasting by skipping breakfast didn’t see any change in body weight. Other studies targeting participants with obesity found this method was no more effective than simply reducing calorie intake over the long run,” explained Camille Lassale, ISGlobal researcher and senior co-author of the study.
Chrononutrition and the Body’s Internal Clock
“Our research is part of a growing field known as ‘chrononutrition’, which examines not only what we eat but also when and how often we eat,” noted Anna Palomar-Cros, a researcher with ISGlobal at the time of the study, now at IDIAP Jordi Gol. “This area is based on the idea that irregular eating patterns can disrupt the circadian system, our internal clocks that regulate daily cycles and related physiological processes,” she added.
Earlier Meals Linked to Broader Health Benefits
This study builds on previous ISGlobal research in chrononutrition, which has shown that eating dinner and breakfast earlier correlates with a reduced risk of cardiovascular conditions and type 2 diabetes. This reinforces the significance of meal timing in long-term health.
