- Around 8 am, there is breakfast. Lunch is ready by 12 pm and the evening meal is finished by 6 pm. Such eating times could be typical for a person who aligns with their biological rhythm. However, for many people, different times should apply. Professor Annette Buyken explains this in her conversation with ntv.de. The scientist was involved in a recent study on this topic.
"There are inappropriate meal times"
ntv.de: How do we eat against our "inner clock"?
Professor Annette Buyken: Each of us has an "inner clock," which determines when we sleep, but also eat or do sports, when we can structure our day freely, for example on free days. If we really prefer to sleep late and, due to social framework conditions such as university, school, or work, have to get up early and eat breakfast early, then we are eating against our inner clock. The same applies to social events, where people who prefer to go to bed early and therefore eat dinner early may end up eating "too late." This is also referred to as "eating against the inner clock." All people, who are neither owls nor larks, have fewer problems with this, as the framework conditions fit well with their own inner clock.
What happens when one eats against their inner clock for an extended period, i.e., several months or even years?
It is assumed that our "inner clock" falls out of sync. Eating meals at "inappropriate" times leads to desynchronization between the central timekeeper, which is influenced by daylight, and the timekeepers in our peripheral organs. This disrupts the circadian rhythm, which many of our metabolic processes depend on, and contributes to long-term health issues such as diabetes or coronary heart disease. (Note: The circadian rhythm refers to the ability of an organism to synchronize physiological processes on a period length of approximately 24 hours. The most important circadian rhythm is the sleep-wake rhythm.)
How did you determine which students were the earliest larks or the latest owls?
In our study, we first asked over 300 students to complete a questionnaire on their so-called "chronotype" (inner clock) determination. This questionnaire - the Munich Chronotype Questionnaire (MCQT) - has already been used in many studies and validated. It asks about weekly and weekend sleep patterns and calculates the chronotype from that. For the intervention study, we then invited the students with the earliest (larks) and latest (owls) chronotypes. Before the intervention, the participants wore an accelerometer. This allowed us to determine when they actually slept and woke up on weekends - free days.
What effect does a high blood sugar level have and why should one avoid such peaks?
A high blood sugar level can lead to various health issues, such as increased thirst, frequent urination, fatigue, and blurred vision. Over time, high blood sugar levels can damage the nerves and blood vessels, leading to complications such as kidney damage, nerve damage, and cardiovascular disease. It is recommended to maintain stable blood sugar levels through balanced meals and regular physical activity.
A high Glucose level causes so-called "oxidative stress," meaning harmful oxygen compounds, known as "reactive oxygen species," are produced, leading to an increased inflammatory response. This damages vessels in the long term and contributes to a condition called insulin resistance. If this is repeatedly caused, the risk of developing diabetes or coronary heart disease increases. In healthy individuals, a high Glucose level triggers a very quick insulin response, meaning the Glucose level is only briefly elevated. In people with insulin resistance, less sugar gets into the body cells, resulting in a correspondingly longer elevated Glucose level.
Did your examination yield an unexpected result?
We knew from literature that the ability to metabolize Glucose is poorer in the evening than in the morning. Our test meal, which had to be consumed morning and evening at 7 am and 20 pm respectively, was chosen to elicit a high Glucose response. We had expected both owls and larks to exhibit a circadian rhythm in their Glucose response, meaning they would perform better with the test meal in the morning than in the evening. We assumed that the evening problem would be greater in larks than in owls because they, like all of us, are more insulin resistant in the evening and had to eat the meal against their internal clock - too late. We were surprised to find that owls did not exhibit a circadian rhythm: owls had the same response in the morning as in the evening, despite being less insulin resistant in the morning. For owls, it was indeed a problem that they had to consume the meal "too early," against their internal clock.
Exactly how could owls exchange the "unfavorable" carbohydrates at the too-early breakfast, and is it better to simply omit the breakfast in this case?
The question of breakfast is a contentious topic, and not eating breakfast can also have unfavorable effects on glucose regulation. However, we know from literature that larks particularly benefit from breakfast. For owls, it is likely sensible to eat later in the morning, i.e., to consume their breakfast as a second breakfast at a time when they would normally eat in the morning on free days. Muesli - especially with whole grain flakes - and fruit and milk products or milk substitute products, supplemented with a few nuts or seeds, are a good alternative to white bread or pretzels. Those who prefer bread can opt for whole grain bread with whole grains.
Is there an idea or a general tip for finding the right time for the intake of carbohydrates, or should they simply be omitted?
One cannot completely avoid carbohydrates, this is also the case with a "low carb" diet. According to us, there are two important things. Firstly: Pay attention at dinner time: since we all have difficulty handling carbohydrates in the evening, whether owl or lark, one should avoid large portions of unfavorable carbohydrates in the evening - so pizza, french fries, white rice, white bread and so on, should be halved and served with vegetables or more often opt for lentil or kale dishes. Secondly: For the owls among us: unfortunately, mornings are not a good time for unfavorable carbohydrates.
Jana Zeh spoke with Professor Anette Buyken.
- The misalignment between eating times and an individual's chronobiological rhythm, as observed in many people, may lead to long-term health issues such as diabetes and coronary heart disease, driven by disruptions in the circadian rhythm and the metabolic processes it regulates.
- Professor Buyken's study involved identifying the earliest larks and latest owls among students by using the Munich Chronotype Questionnaire (MCQT) to determine their 'chronotype' and then analyzing their sleep patterns with the help of accelerometers.
- Regularly consuming meals at inappropriate times, especially high in carbohydrates, can cause insulin resistance and oxidative stress, exacerbating the risk of developing diabetes and other related health conditions. It is recommended to maintain stable blood sugar levels through balanced meals and regular physical activity, adhering to the optimal consumption times for carbohydrates, which often differ based on an individual's chronobiology.
