Summary:
The human circadian system regulates daily rhythms in behaviour and metabolism. Food eaten at different times of the day is processed differently, with variations in glucose tolerance, hormone release and other metabolic functions. Eating also acts as a signal that helps synchronise internal clocks, especially in the liver, gut, pancreas and fat tissue. When eating patterns are out of sync with the body’s natural rhythm, such as during night shift work, this can cause metabolic problems. Studies have linked late or night-time eating to higher risks of obesity, cardiovascular disease and poor metabolic health, but the specific effects on glucose metabolism and diabetes risk are not fully understood. In this study, 92 adult twins were assessed using food diaries and glucose tolerance tests. Eating timing, calorie distribution and meal frequency were recorded, with special focus on the time when half of daily calories had been consumed, also known as the caloric midpoint. Results showed that a later caloric midpoint was consistently linked to poorer insulin sensitivity, higher fasting insulin, and greater body weight and waist circumference, even after accounting for energy intake, sleep, age and sex. These findings suggest that eating later is associated with impaired glucose metabolism. Moving calorie intake to earlier in the day may improve insulin sensitivity. Larger studies are still needed to further verify these results.
Abstract:
Background: Although the contribution of the circadian clock to metabolic regulation is widely recognized, the role of eating timing in glucose metabolism and diabetes risk remains insufficiently studied. This study aimed (i) to investigate the link between the eating timing pattern relative to individual clock and glucose homoeostasis and (ii) to explore the contribution of genetic and environmental factors to eating timing parameters. Methods: In 92 adult twins (NCT01631123), glycaemic traits were assessed using the oral glucose tolerance test. Parameters of eating timing pattern (eating timing itself, daily calorie distribution, and eating frequency) were extracted from five-day food records. Caloric midpoint defined as the time point at which 50% of daily calories are consumed. Circadian timing of eating was determined as a time interval between the clock time of eating and a corrected midpoint of sleep, a chronotype marker. Heritability of eating timing components was estimated by comparing correlations within monozygotic and dizygotic twin pairs and fitting genetic structural equation models. Findings: Among components of eating timing, the most associations were found for the circadian time of caloric midpoint (CCM). Later CCM was significantly associated with poorer insulin sensitivity, i.e. with lower ISI Stumvoll (β = 0.304, p = 5.9 × 10−4) and higher HOMA-IR (β = −0.258, p = 0.011) indices, as well as with higher fasting insulin levels (β = −0.259, p = 0.013), even after the model adjustment for sex, age, daily energy intake, and sleep duration. Later CCM also demonstrated robust associations with higher BMI and waist circumference. All eating timing components showed high or moderate heritability and were strongly related to individual sleep timing. Interpretation: Later eating timing in relation to an individual internal clock is associated with lower insulin sensitivity. Shifting the main calorie intake to earlier circadian times may improve glucose metabolism, but genetic factors could influence the feasibility and effectiveness of eating-timing based interventions. The findings should be investigated in a larger cohort.
Article Publication Date: 29/04/2025
DOI: 10.1016/j.ebiom.2025.105737
