Nutritional guidelines recommend regular eating patterns, yet media headlines often highlight the benefits of intermittent fasting. While weight gain is a result of an imbalance between energy intake and expenditure, could the same meal have different effects on our bodies depending on the time of day it is consumed? This is the question I explored in my bachelor’s thesis for the Bachelor's Programme in Molecular Biosciences at the University of Helsinki.
The Master Clock Regulates Biological Rhythms
The central regulator of our circadian rhythm, also known as the "master clock," is the suprachiasmatic nucleus located in the hypothalamus of the brain. This master clock controls various functions such as hormone secretion, the sleep-wake cycle, and metabolism. For good health, it is preferable to maintain regular eating and sleeping patterns.
Several population studies have found higher rates of obesity and chronic diseases, such as cardiovascular diseases, among shift workers. For example, a cross-sectional study (Study 1) involving thirty thousand participants found that obesity and elevated blood lipid levels, which increase the risk of cardiovascular disease, were most common among shift workers. A defining feature of shift work is its chronic misalignment with the body’s natural rhythms. This is believed to be a contributing factor to the health risks associated with shift work.
Late Night Eating Is Linked to Obesity at the Population Level
Observational studies suggest that late night eating is associated with obesity (Study 2). However, this connection is largely mediated by an increase in total energy intake. In other words, the more meals are consumed in the evening, the more energy is typically consumed overall, which, over time, can lead to weight gain. Most people can probably relate to eating at restaurants or snacking rather in the evening than in the morning. Another reason for increased food intake in the evening could be that evening meals trigger a lower release of satiety hormones than morning meals (Study 3). What remains unclear is how late night eating affects obesity when food choices are healthy.
How Meal Timing Affects the Body
If a morning and evening meal have the same nutritional content, what is the difference in their responses? A morning meal results in a significantly lower insulin response compared to an identical evening meal (Study 4). As the day progresses, a mild form of “insulin resistance” seems to develop, meaning that cells become less responsive to insulin, leaving more glucose in the bloodstream. This may increase the risk of type 2 diabetes and negatively affect blood lipid levels, which can further raise the risk of cardiovascular disease. There is also evidence that post-meal thermogenesis (the energy the digestive system uses to process the meal) is lower in the evening than in the morning, leading to reduced total energy expenditure. Late night eating may also alter gene expression in adipose tissue activating signaling pathways that favor energy storage (Study 5). However, these mechanistic explanations do not directly prove that eating late causes weight gain.
One proposed explanation for the metabolic downsides of “mistimed” meals is that eating at the “wrong time” leads to desynchronization with the body’s master clock, disrupting the circadian rhythms of cells. It appears that the body prefers consistent daily rhythms and a sufficiently long overnight fasting period. The gut microbiota is also considered a factor that may influence fat tissue formation through its role in regulating the circadian rhythm.
So, Should I Eat in the Evening?
Currently, there is no strong evidence that completely avoiding eating in the evening would benefit health. For example, a post-exercise evening snack can support muscle protein synthesis and enhance recovery. For certain population groups, such as children and the elderly, regular and frequent meals help maintain health and functional capacity and ensure adequate energy and nutrient intake. A reasonably sized meal before bedtime may also be relaxing and support falling asleep, whereas a heavy meal might make it more difficult to do so. However, in terms of weight management and blood sugar control, reducing evening calorie intake could be beneficial. Ultimately, the most important thing is to find a meal schedule that suits your lifestyle and stick to it as consistently as possible each day.
Summary:
- Late night eating is associated with obesity, but this link is mainly explained by higher overall energy intake among evening eaters.
- People tend to eat more in the evening because the production of satiety hormones is lower, and the environment tends to promote less healthy food choices in the evening compared to the morning.
- Mechanisms independent of energy intake have also been identified, such as a higher glucose response to evening meals and the activation of signaling pathways that favor energy storage.
- For effective weight management, the most important factors are health-promoting food choices and a meal pattern that is sustainable in everyday life.
Main Text
Emma Järvensivu
Student of Nutritional Science at the University of Helsinki
Intern at the Mind Nutrition and RAVI projects
References
Study 1: Karlsson, B., Knutsson, A., & Lindahl, B. (2001). Is there an association between shift work and having a metabolic syndrome? Results from a population based study of 27 485 people. Occupational and Environmental Medicine, 58(11), 747–752. https://doi.org/10.1136/oem.58.11.747
Study 2: Davis, R., Rogers, M., Coates, A. M., Leung, G. K. W., & Bonham, M. P. (2022). The Impact of Meal Timing on Risk of Weight Gain and Development of Obesity: a Review of the Current Evidence and Opportunities for Dietary Intervention. Current diabetes reports, 22(4), 147–155. https://doi.org/10.1007/s11892-022-01457-0
Study 3: Gallant, A., Lundgren, J., & Drapeau, V. (2014). Nutritional Aspects of Late Eating and Night Eating. Current Obesity Reports, 3(1), 101–107. https://doi.org/10.1007/s13679-013-0081-8
Study 4: Bo, S., Fadda, M., Castiglione, A., Ciccone, G., De Francesco, A., Fedele, D., Guggino, A., Parasiliti Caprino, M., Ferrara, S., Vezio Boggio, M., Mengozzi, G., Ghigo, E., Maccario, M., & Broglio, F. (2015). Is the timing of caloric intake associated with variation in diet-induced thermogenesis and in the metabolic pattern? A randomized cross-over study. International Journal of Obesity, 39(12), 1689–1695. https://doi.org/10.1038/ijo.2015.138
Study 5: Vujović, N., Piron, M. J., Qian, J., Chellappa, S. L., Nedeltcheva, A., Barr, D., Heng, S. W., Kerlin, K., Srivastav, S., Wang, W., Shoji, B., Garaulet, M., Brady, M. J., & Scheer, F. A. J. L. (2022). Late isocaloric eating increases hunger, decreases energy expenditure, and modifies metabolic pathways in adults with overweight and obesity. Cell Metabolism, 34(10), 1486-1498.e7. https://doi.org/10.1016/j.cmet.2022.09.007