How does sugar affect relaxation exercises? A new study conducted by researchers from the University of Konstanz provides revealing insights into the connection between blood glucose and the autonomic nervous system: Sugar intake counteracts relaxation.
A little sugar before a test, a piece of chocolate before an important negotiation, a muesli bar before a marathon – the important role glucose plays in dealing with stressful situations has been well researched. When we consume sugar, the body reacts more strongly to stress by releasing more cortisol. In addition, our heart rate remains elevated for a longer period of time. This means that more energy is available in acute stressful situations. The negative long-term consequences are also known: increased risk of hypertension, obesity and cardiovascular diseases.
What has been less researched to date is how sugar intake affects relaxation. That is why researchers from the group of Jens Pruessner, professor of neuropsychology at the University of Konstanz, conducted a corresponding study, which has now been published in International Journal of Psychophysiology. Jens Pruessner summarizes the results of the study: “If your stomach is full, relaxation exercises will not be as effective.”
Konstanz’s research team aims to understand the role the body’s energy systems play in relaxation and what effect individual metabolic factors – for example blood glucose levels – have. The autonomic nervous system, which includes the sympathetic and parasympathetic nervous systems, controls various processes in our body, such as heart rate and breathing. “Our heart has an internal pacemaker that determines how fast it beats. While sympathetic activity has a stimulating and activating effect in times of stress, parasympathetic activity acts as a vagal brake, slowing down the heart rate,” explains Maria Meier, first author of the study and a postdoctoral researcher in Jens Pruessner’s research group.
Sweet relaxation?
The study involved 94 healthy adults. The participants, who had fasted before coming to the lab, were randomly assigned to consume either a glucose-containing drink or water. Then one half received a relaxing massage, while the other half rested without direct intervention. Cardiac activity was measured continuously. The authors later calculated heart rate variability, a measure of parasympathetic nervous system activity. They also assessed the pre-ejection period, which is a measure of sympathetic nervous system activity.
What effect did sugar have on this experiment? All participants reported that they found the massage or rest phase mentally relaxing. This was also reflected in the measured heart activity: The relaxation techniques activated the parasympathetic nervous system, regardless of whether sugar had been consumed beforehand or not. That massages provide deeper relaxation compared to simple rest has already been shown in previous studies.
At the same time, the sympathetic nervous system was activated after taking sugar. “This means: Although the participants subjectively felt relaxed, their sympathetic nervous system did not slow down, but kept the body in a higher state of arousal. As a conclusion from the results of our tests we can say that sugar impairs the body’s ability to relax,” says neuropsychologist Meier.
So no soda, no ice cream before the massage? “Enjoying a sweet snack is often associated with relaxing situations – a chocolate bar or ice cream with a movie, a slice of cake at the weekend with the family. In fact, the constant sympathetic activation after sugar intake seems to limit the ability to relax. So if you want to relax, e.g. Jens Prussner.
The study also leads to another conclusion for the researchers: “To make valid statements, we cannot look at one system in isolation – that is, either the sympathetic or the parasympathetic system – because otherwise we would overlook some effects,” says Maria Meier. “If we had only investigated the parasympathetic nervous system, we would not have observed the significant effect on the sympathetic nervous system.”
