Late Eating is Associated with Impaired Glucose Metabolism

Our metabolic processes differ depending on the time of day and many of them are more active in the morning than in the evening. Although studies show that eating late in the day is associated with an increased risk of obesity and cardiovascular diseases, little is known about how the time when we eat affects glucose metabolism and to what extent this is genetically defined. Prof. Olga Ramich from the German Institute of Human Nutrition Potsdam-Rehbruecke (DIfE) and her team recently investigated this in a twin cohort. The article was published in the journal “eBioMedicine.”


Metabolism Follows the Internal Clock

The circadian system is a hierarchically structured 24-hour time control system in the body that regulates behavior and metabolism via a central clock in the brain and peripheral clocks in organs such as the liver or pancreas. As a result, our metabolic processes differ depending on the time when we eat, which leads to diurnal fluctuations in glucose metabolism and the release of hormones after a meal. Food intake itself acts as an important timer that synchronizes our internal clocks. Decoupling meal times from the natural light-dark rhythm, e.g. when working at night, can lead to an internal clock disorder and negative metabolic changes.


Does Late Eating Make You Ill?

Previous studies have shown that eating late at night is associated with an increased risk of obesity and cardiovascular diseases. However, little is known about how exactly the timing of food intake interacts with the individual circadian rhythm and thus influences glucose metabolism and the risk of diabetes. It is also unclear which mechanisms determine one’s individual eating behavior, as it depends on the interaction of cultural, personal, physiological and genetic factors.

Against this background, Olga Ramich, Heisenberg Professor at the Charité – Universitätsmedizin Berlin and at the DIfE, has investigated how the timing of food intake during the day is associated with glucose metabolism and insulin sensitivity. Ramich, who also conducts research at the German Center for Diabetes Research (DZD), and her team wanted to find out the genetic and environmental parameters that affect individual eating habits.


Twins Provide Information

They used data from the NUtriGenomics Analysis in Twins (NUGAT) study, with the participants being 46 identical and fraternal twin pairs without diabetes. The test subjects kept a food diary of the times and quantities they ate for five days. The scientists determined the individual sleep-wake rhythm (chronotype) of the participants and carried out various metabolic tests, such as a blood glucose load test. Furthermore, they also determined the circadian timing of eating, i.e., when someone eats during the day, in comparison to their individual biological circadian rhythm, rather than the specific time of the day.


Circadian Timing of Eating

When someone eats during the course of a day in relation to the individual biological daily rhythm is measured as the interval between mealtime and the midpoint of sleep. 

The midpoint of sleep describes the time that lies exactly in the middle between falling asleep and waking up. It is a measure of the chronotype – in other words, whether someone is an early riser or a night owl.


Eating Earlier Promotes a Healthy Metabolism

An important parameter that the scientists determined was the circadian caloric midpoint (CCM) of the test subjects. The CCM describes the time point in the day at which 50% of daily calories are consumed. A later CCM therefore means that someone eats mainly later in the day – in relation to the individual chronotype.

“People who ate their main calories earlier in the day had better insulin sensitivity,” explains Ramich, who heads the Department of Molecular Metabolism and Precision Nutrition at the DIfE. “On the other hand, subjects who consumed their main calories late in the day showed poorer insulin sensitivity, which is associated with a higher risk of type 2 diabetes.” In addition, they had a higher body mass index and a larger waist circumference.


The Influence of Genes on Eating Times

To investigate the influence of genes on eating times, the researchers compared the eating behavior of identical twins (100 percent identical genes) with that of fraternal twins (approx. 50 percent identical genes). Using special mathematical models, they were able to estimate the extent to which the timing of eating can be attributed to genes, shared environment or individual experiences.

The study shows that various parameters of the daily eating pattern are affected by our genes by up to 60 percent.


Conclusion: Personalized Nutrition Needs New Approaches

Shifting the main calorie intake to earlier circadian times might improve glucose metabolism and protect against type 2 diabetes and obesity. “However, as eating times are partly hereditary, some people may find it difficult to change their habits,” Ramich points out. “Further validation studies and clinical trials are needed to better understand the effectiveness of mealtime-based interventions.”


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