Our Bodies Burn More Calories from Food in the Morning, Study Suggests

What's new

New research has identified an endogenous circadian rhythm in diet-induced thermogenesis (DIT), the energy expended by the body to digest, absorb, and metabolate food. This internal rhythm dictates that the body burns more calories from food in the biological morning compared to the biological evening, independent of external influences like sleep, activity, or light exposure [1]. This finding provides a potential physiological mechanism explaining why eating later in the day has been linked to increased body weight.

Previous studies have observed differences in DIT based on meal timing, but it has been unclear whether these variations were due to the body's internal clock or external factors such as sleep-wake cycles, physical activity, or light exposure. This study specifically isolated the endogenous circadian rhythm of DIT, revealing a significant peak in the biological morning and a trough in the biological evening [1].

The science behind it

The study involved 16 healthy adults classified as overweight or obese. To isolate the endogenous circadian rhythm of DIT from environmental and behavioral influences, participants underwent a rigorous 'Constant Routine' protocol. This involved 36 hours of continuous wakefulness, maintaining a semi-recumbent posture, exposure to dim light, and consuming identical test meals every six hours [1]. This controlled environment allowed researchers to observe the body's internal biological rhythms without interference from daily routines.

Researchers measured participants' energy expenditure after each meal throughout the 36-hour period. The results demonstrated a clear endogenous circadian rhythm in DIT. The peak thermogenic response occurred during the biological morning (equivalent to approximately 8 AM in a typical day), while the lowest response was observed in the biological evening (around 8 PM) [1]. The difference between the peak and trough was substantial, showing a 44% amplitude in DIT, translating to about 10 kilocalories over a four-hour period. Even after accounting for the body's fasting energy expenditure, the circadian rhythm in DIT remained significant, with a slightly reduced amplitude of 29% (approximately 7 kilocalories over four hours) [1].

Exploratory analyses also indicated that this internal circadian rhythm in DIT was not influenced by participants' prior eating schedules, reinforcing the idea that it is an intrinsic biological process rather than a learned response [1].

What it means in practice

These findings suggest that the timing of meals could play a more significant role in weight management than previously understood, beyond just the caloric content or macronutrient composition of the food. Consuming meals earlier in the day, when the body's DIT is naturally higher, might lead to more efficient calorie burning and potentially contribute to better weight control [1]. Conversely, eating later in the evening, when DIT is at its lowest, could mean that the body expends less energy processing the same amount of food, potentially contributing to weight gain over time. This research provides a physiological basis for the growing interest in chrononutrition and time-restricted eating, suggesting that aligning meal times with our internal biological clock could be beneficial for metabolic health.

For individuals looking to optimize their metabolic processes, these results lend support to the idea of front-loading caloric intake earlier in the day. While more research is needed to translate these findings into specific dietary recommendations, understanding this endogenous rhythm can inform personalized approaches to eating patterns, especially for those managing weight or metabolic conditions [1].

Caveats

While this study provides compelling evidence for an endogenous circadian rhythm in DIT, it is important to note several considerations. The study population consisted of healthy adults who were overweight or obese, so the findings may not be directly generalizable to individuals with different body mass indexes or specific metabolic disorders [1]. Additionally, the Constant Routine protocol, while excellent for isolating endogenous rhythms, is an artificial environment. Real-world conditions involve numerous confounding factors like varying activity levels, light exposure, and sleep patterns that were strictly controlled here. Therefore, the magnitude of this effect in daily life might differ [1].

The observed difference in calorie burning, while statistically significant, amounted to approximately 7-10 kilocalories over a four-hour period. While this difference could accumulate over time, its practical significance for substantial weight loss in isolation would need further investigation in longer-term studies. Finally, this research focused on DIT, which is only one component of total daily energy expenditure. Other factors, such as basal metabolic rate and physical activity, also play crucial roles in energy balance.

Source: [1]