- Our bodies process food differently depending on the time of day, with metabolism generally more active in the morning.
- While late eating is linked to obesity and heart disease, its exact effects on glucose metabolism and the role of genetics are still unclear.
- A new twin study from Germany now offers fresh insight into how meal timing interacts with our internal clocks and overall Health.
The circadian system is a complex 24-hour timekeeping system that controls behaviour and metabolism through a central clock in the brain and additional clocks in organs such as the liver and pancreas.
Because of this system, our metabolism responds differently depending on when we eat, resulting in daily variations in glucose processing and hormone release after meals.
Food intake itself serves as an important signal that helps align our internal clocks.
Eating at times that are out of sync with the natural light-dark cycle, for example, when working night shifts, can disrupt these internal clocks and lead to adverse metabolic effects.
Researchers at the German Institute of Human Nutrition Potsdam-Rehbrücke (DIfE) have recently investigated the link between blood sugar metabolism and evening eating times using data from a twin study conducted in 2009–10.
Their findings are published in the journal
Earlier research has shown that consuming meals late at night is linked to a higher risk of obesity and
However, we still do not fully understand how meal timing interacts with a person’s individual circadian rhythm and affects glucose metabolism and diabetes risk.
In addition, the specific mechanisms behind when and why people eat remain unclear, as eating habits are shaped by a mix of cultural, situational, genetic and other biological factors.
The timing of food intake in relation to a person’s biological daily rhythm can be assessed by looking at the gap between mealtime and the midpoint of sleep.
The sleep midpoint refers to the time exactly halfway between falling asleep and waking up, and it indicates a person’s chronotype, that is, whether they tend to be an early bird or a night owl.
The NUGAT study was carried out between 2009 and 2010 at the German Institute of Human Nutrition Potsdam-Rehbrücke (DIfE).
To recruit participants, researchers used a twin registry (HealthTwiSt, Berlin, Germany) and public advertisements. In total, 92 individuals (46 pairs of identical and fraternal twins) took part.
While the twins completed two nutritional interventions during the study, these interventions were not relevant to the results discussed here.
All participants underwent comprehensive metabolic assessments, which included physical exams, medical history reviews, body measurements, and glucose tolerance tests. Their individual chronotypes were identified using a questionnaire.
In addition, each participant kept handwritten food diaries over 5 consecutive days (3 weekdays and 2 weekend days), recording the start and end times of each meal along with details on the type and quantity of food consumed.
This approach helped capture a realistic picture of their usual eating habits.
Overall, the analysis indicated that people who tended to have their final meal later in the day and closer to bedtime also had less effective glucose (blood sugar) metabolism at the end of the day, as they had lower insulin sensitivity.
This may suggest that better regulating our meal times may help maintain our metabolic Health.
Destini Moody, RD, CSSD, LD, registered dietitian at Top Nutrition Coaching, not involved in this research, reviewed the study and spoke to Medical News Today about its findings.
“In general, I’m skeptical about adjusting the timing of one’s eating in the hopes of controlling weight or blood sugar unless you are diabetic,” Moody told us.
“My colleague and I used to joke that your digestive system doesn’t work in shifts, meaning it doesn’t “clock out” after a certain time of day and decide to start storing everything as fat,” she added.
“While it’s well known that eating timing and meal composition is critical for controlling blood sugar and insulin action in those with diabetes, this study was performed on healthy individuals with normal pancreatic function and no other metabolic disturbances. Even without diabetes, those with metabolic syndrome should be careful about their level of insulin resistance, but none of the subjects fell under this category either given their BMI and waist circumference. The average age of subjects was also 32, which is relatively young.”
– Destini Moody, RD, CSSD, LD
“As far as the genetic component of how eating timing influences insulin sensitivity, this is a mixed bag, [too]” Moody further noted. “On the one hand, it’s an interesting finding, but on the other hand, genetic factors are difficult to detect and control.”
“In general, blood sugar variations are a natural part of digestion and metabolism, and I would urge the public to refrain from stressing about the effects food may have on their blood sugar unless they have metabolic ailments like type 2 diabetes,” she advised.
However, she did emphasize that it is always important to pay attention to how much fiber we ingest, and how much of it comes from refined grains.
Moody explained:
“Foods with added sugars, that have been made with refined grains, and are generally low in fiber will raise blood sugar quickly and send it crashing back down due to a rebound effect. This tends to make people even hungrier and even cause fatigue, which is why you feel sleepy after having meals high in these types of carbs. Luckily, eating whole grains and high fibers fruits and vegetables along with lean protein can not only help mitigate this effect, but often results in a healthier diet overall that helps prevent the risk of chronic disease.”
