Childhood obesity is one of the major global public health challenges today. According to the World Obesity Federation, by 2035, two out of every five children aged 5 to 19 are expected to be overweight or obese.
Spain is no exception to this worrying trend, ranking twentieth among countries with the highest proportion of children with elevated body mass index (BMI). The ALADINO study (Food, Physical Activity, Child Development, and Obesity), conducted by the Spanish Agency for Food Safety and Nutrition in 2023, reported that 20.2% of children aged 6 to 9 were overweight, and 15.9% were obese.
A New Perspective: Chrono-nutrition
In this context, eating habits play a key role. But beyond what and how much children eat, a growing focus in recent years has been on chrono-nutrition—the study of how the timing of food intake influences metabolism. This approach is based on the idea that our biological rhythms, regulated by the circadian clock, affect metabolic processes and bodily regulation.
Guided by this concept, the VALORNUT research group at Complutense University of Madrid conducted a study to analyze whether meal timing and the duration of the eating window—the interval between the first and last meal of the day—impact diet quality and nutritional status in Spanish children.
The Study
The study included 880 schoolchildren aged 8 to 13 from five Spanish provinces: A Coruña, Barcelona, Madrid, Seville, and Valencia. Data were collected through parent questionnaires and school evaluations, including information on meal schedules, diet quality, biochemical parameters, and anthropometric measurements.
Key Findings
One striking finding was that, unlike some previous adult studies, neither a late breakfast (after 8:53 a.m.), a late dinner (after 9:10 p.m.), nor a prolonged eating window (more than 12 hours between first and last meal) was directly linked to poorer nutritional status or increased obesity in the children. However, these patterns were not free from negative metabolic effects.
Children who ate breakfast later showed lower blood glucose and LDL cholesterol (“bad cholesterol”) levels, and higher HDL cholesterol (“good cholesterol”) levels.
On the other hand, a prolonged eating window was associated with less favorable glucose and cholesterol profiles, as well as higher atherogenic indices—markers indicating increased long-term cardiovascular risk.
Finally, both late breakfasts and late dinners correlated with poorer overall diet quality. Generally, eating the first or last meal late was linked to less meal planning and more improvised eating, which negatively affected nutritional quality.
The Metabolic Impact
These results may be explained by mechanisms related to circadian rhythms: during the night, the body expends less energy, processes carbohydrates and fats less efficiently, and hormone synthesis and action—such as insulin, leptin, and ghrelin, which regulate metabolism and satiety—are altered.
Conversely, very early breakfasts may coincide with high melatonin levels that remain elevated from the night, potentially suppressing insulin release or insulin sensitivity, leading to glucose intolerance.
An important observation was that 60% of children with prolonged eating windows also ate late dinners and had shorter sleep durations. Sleep deprivation combined with these eating patterns may worsen metabolic effects, especially during childhood growth.
Practical Recommendations
The main advice from the study is to advance dinner time and shorten the daily eating window—ideally eating within less than 12 hours from the first to the last meal—focusing food intake during the day when the body is most metabolically active.
Although observational, these findings strengthen the idea that when children eat is a crucial factor in preventing childhood overweight and obesity—particularly in countries like Spain where late dinners are common. Establishing good habits from an early age is key to tackling this public health challenge.
The VALORNUT group suggests continuing research into this area, including factors such as chronotype (whether a child is more active in the morning or evening), meal duration, and melatonin levels, to better understand how the internal clock influences health from childhood onward.