Study links early breakfast and fasting to lower BMI in middle-aged adults

Study of 7,000 adults finds links between meal timing and health, with 3,000 returning for follow-up after five years

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The timing of meals — not just their content — could play a significant role in maintaining a healthy body weight, according to a new five-year study led by the Barcelona Institute for Global Health (ISGlobal). Researchers found that middle-aged adults who ate breakfast early and extended their overnight fasting period tended to have lower Body Mass Indexes (BMIs).

The findings, published in the International Journal of Behavioral Nutrition and Physical Activity, are part of a growing field known as chrononutrition, which explores how eating schedules align with the body’s natural circadian rhythms.

The study tracked over 7,000 adults aged 40 to 65, all part of the GCAT | Genomes for Life project in Spain. Participants first provided information on diet, lifestyle, and meal timing in 2018. After five years, more than 3,000 returned for a follow-up with updated health data.

The results indicated that those who started their day with an early breakfast and had a longer overnight fast generally had lower BMIs. “Extending the overnight fast could help maintain a healthy weight if accompanied by an early dinner and breakfast,” explained Luciana Pons-Muzzo, an ISGlobal researcher at the time of the study. “This may align better with circadian rhythms and support appetite regulation and energy expenditure.”

The study also found significant gender-based patterns. On average, women had lower BMIs, consumed healthier diets, and drank less alcohol, though they reported worse mental health. Women were also more likely to take on caregiving and domestic responsibilities.

In contrast, a small subgroup of men who delayed their first meal until after 14:00 — effectively skipping breakfast and fasting for around 17 hours — exhibited less healthy behaviours. These included higher rates of smoking and alcohol consumption, lower physical activity, and poorer diet quality. This group also had lower educational levels and higher unemployment rates.

“These men practiced a form of intermittent fasting by skipping breakfast, but we found no association between that habit and improved weight outcomes,” said Camille Lassale, ISGlobal researcher and senior co-author. “Other studies in people with obesity have shown similar findings — skipping breakfast isn’t necessarily an effective weight-loss tool.”

The research adds to ISGlobal’s growing body of work in chrononutrition. Previous studies have linked early dinner and breakfast habits with reduced risks of cardiovascular disease and type 2 diabetes.

“Chrononutrition looks at not just what we eat, but when and how often,” said Anna Palomar-Cros, who co-authored the study. “Disrupting eating patterns can conflict with the circadian system — the body’s internal clock — potentially affecting weight, metabolism, and overall health.”

While the study suggests a potential link between meal timing and body weight, researchers caution that more evidence is needed before making broad dietary recommendations. Nonetheless, the findings underscore the importance of aligning eating habits with the body's natural rhythms to support long-term health.