To manage weight effectively, it’s crucial to pay attention not just to what we consume, but also to when we eat. A recent study published in the International Journal of Behavioral Nutrition and Physical Activity highlights two key habits linked to a reduced body mass index (BMI) over time: extending the overnight fast and having breakfast early. This research was spearheaded by the Barcelona Institute for Global Health (ISGlobal), a center funded by the “la Caixa” Foundation.
The study included over 7,000 participants aged 40-65 from the GCAT | Genomes for Life project managed by the Germans Trias i Pujol Research Institute (IGTP). In 2018, the volunteers responded to surveys regarding their weight, height, eating patterns including meal times, lifestyle choices, and economic status. Five years later, in 2023, more than 3,000 participants returned for follow-up evaluations, where their measurements were taken again and additional surveys were filled out.
Understanding the results
“Our findings, consistent with other recent research, indicate that a longer overnight fast might assist in maintaining a healthy weight, especially when paired with an early dinner and breakfast. This could be because eating earlier aligns better with natural body rhythms, enhancing calorie burning and appetite control, which are vital for weight management. However, it is too early to make definitive claims; further evidence is needed to strengthen these recommendations,” states Luciana Pons-Muzzo, who was an ISGlobal researcher during the study and is currently affiliated with IESE Business School.
Differences by gender
When analyzing the data by gender, it was found that women generally had a lower BMI compared to men, were more adherent to the Mediterranean diet, consumed less alcohol, experienced poorer mental health, and took on more responsibilities related to household or family care.
The research team employed a statistical method known as ‘cluster analysis‘ to categorize individuals displaying similar traits. They discovered a small group of men who had their first meal after 14:00, averaging a fast of 17 hours. This group exhibited less healthy lifestyles, with higher rates of smoking and drinking, lower physical activity levels, and lesser adherence to the Mediterranean diet. Additionally, they had lower educational attainment and a higher likelihood of being unemployed. These trends were not identified in any female groups.
About intermittent fasting
“There are various methods to practice ‘intermittent fasting’, and our study pertains to one approach, which is overnight fasting. We found that in a subgroup of men who skipped breakfast as a form of intermittent fasting, this practice did not lead to weight loss. Other studies involving obese participants have indicated that this method is no more effective than simply reducing caloric intake for long-term weight loss,” explains Camille Lassale, a senior researcher at ISGlobal and co-author of the study.
“Our research is part of a growing field called ‘chrononutrition’, which examines not just what we eat, but also when we eat and how often. This research is based on the understanding that irregular eating habits can disrupt the circadian system, which includes the internal clocks regulating day-night cycles and the physiological processes associated with them,” adds Anna Palomar-Cros, a researcher at ISGlobal during the study, now at IDIAP Jordi Gol.
Previous research
This study builds on ISGlobal’s ongoing research on chrononutrition, which in recent years has published two other studies yielding similar conclusions. These earlier studies indicated that having dinner and breakfast earlier in the day is linked to a reduced risk of cardiovascular diseases and type 2 diabetes.
