Disturbed clocks: How eating and exercise influence the timing of our internal clocks

A new study shows that the timing of the different clocks in our body depends on multiple stimuli. This was investigated in the liver- and muscle clock of rats, where only a combination of eating and exercise was able to cause a shift of the internal muscle clock.

More and more people are diagnosed with obesity or type 2 diabetes. An important cause of this increase is the timing of eating and sleeping. People who are active at night such as those working night-shifts, experience a metabolic mismatch in their bodies, which increases the likelihood of metabolic problems. But how does this happen?

Our braincontains a biological clock. The period of this clock is not exactly 24 hours. How do we ensure that this biological clock knows when the day begins and ends? “This clock needs to be reset every day,” explains Professor Dries Kalsbeek, the group leader of this study. “This reset is mostly caused by light that enters through the eye. Every morning you open your eyes, this clock will reset.”

However, this biological clock in the brain is not the only clock present in your body. Different organs use the same molecular mechanism to keep track of time: the peripheral clocks. These clocks do not have a rhythm of exactly 24 hours either. Therefore, these clocks also need to be reset. “This resetting of the peripheral clocks is one of the main functions of the clock in our brain”, Kalsbeek explains. “It is the only clock directly connected to the eye, so this clock knows what the correct time is. This information is then shared with the peripheral clocks via hormones or nerve signals.”

Two signals

But the peripheral clocks do not only react to signals from the brain clock. Research has shown that these clocks are also sensitive to the energy balance in your body. When you eat and take in energy, or when you are active and expand energy, the peripheral clocks register that. This can lead to a mismatch between the signals from the brain and the signals from your body. “The central brain clock and the peripheral clocks do not always align. When people are active or eat at night, the central clock says it is dark and that you should be resting, which contradicts with the signals from your body indicating that you are active. So,  the two messages do not match.” This mismatch in the different peripheral clocks is an important hypothesis to explain metabolic problems, like type 2 diabetes.

Timing between eating and exercise

It is already known for some time that the liver clock is reset by the timing of food intake. But how can we get the clock in your muscles to run properly? Professor Kalsbeek and his colleagues investigated this in rats. They had the rats run in a running wheel at different times of the day. Rats are nocturnal animals, and their biological clock signals them to be active at night. “Even though the rats were only running during the day, the muscle clock continued to operate on a nocturnal rhythm. However, when we also restricted the food intake of these rats to the daytime, not only the liver clock shifted, but we saw that also the muscle clock suddenly began to shift.” Thus, the timing of the liver clock merely depends on the timing of food intake, but the timing of the muscle clock depends on the timing of both eating and exercising. “To shift the clocks of different organs, a combination of different stimuli is needed,” concludes Kalsbeek.

Eating and being active at the same time not only reset the clock in the muscles but also positively affected the rats’ body health. After the experiment, the rats that were active and ate during the day had a much lower fat percentage and body weight than rats that were active during the day but ate during the night.  This information can also be translated to humans: eating and exercising at the same time is important for the timing of the clock in our muscles. The next question is therefore also to investigate when exercising is most effective for people. “There are a lot of variations among studies with the few studies in humans that have been performed so far. To maintain glucose levels, exercising in the evening seems to be most effective. However, when looking at body weight, exercising in the morning appears to be more beneficial.” Therefore, Professor Kalsbeek wants to conduct further research on the timing of exercise. “This is particularly important for people who work on night shifts. We know that working during the day is better for the clocks  in your body, but how can we keep those who have to work at night as healthy as possible?”

Source: Neurobiology of Sleep and Circadian Rhythms

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