Sarah has covered news topics for digital and print publications. She holds a degree in broadcast journalism from the University of Nevada.
Although we use far less energy at night than we do during our waking hours, our bodies are still active and burning calories while we sleep. Our body’s metabolism fluctuates throughout our days, such after meals or while we sleep, and this is called metabolic flexibility.
A recent study from the University of Tsukuba showed that the level of a person’s metabolic flexibility may help indicate their risk level for some metabolic diseases, such as obesity.
One key aspect of this study focused on what is called our respiratory quotient (RQ). This is a measurement of our breathing: how much oxygen we breathe in compared to how much carbon dioxide we breathe out. Researchers studied the RQs of 127 people without obesity for a 24-hour period.
Over the course of that 24-hour period, they measured participants’ RQ every five minutes and examined how their RQs fluctuated.
Our RQs indicate how our bodies are using the three sources of energy that we have: protein, fat, and carbohydrates. When RQ numbers are equal (amount of oxygen breathed in is equal to amount of carbon dioxide breathed out), we use more carbohydrates as energy instead of fat.
When RQ numbers are lower, more fat is used as opposed to carbohydrates. In this RQ state, that person would burn more fat. When our RQs vary over the course of the day, that means we are metabolizing fat and carbohydrates differently at specific times.
This greater the ability for our RQ to vary, the more flexible our metabolism.
According to researchers, the initial findings were surprising, particularly during the participants’ sleep time. Sleep is typically a period of fasting, as we do not eat while we sleep.
It may have been expected to see the RQ numbers decrease and remain low throughout the night in this case, indicating that greater amounts of fat energy would be used during this time of fasting.
However, researchers found that while participants’ RQ values decreased at the beginning of sleep, RQ numbers began to rise again and continued to increase until participants awoke.
Another aspect of the study examined how much the participants’ RQs varied. Researchers divided participants into two metabolic groups: flexible and inflexible.
While the average RQ of the two groups were the same, the team found that the flexible metabolism group’s RQ values, which varied more, were lower at night in comparison to the inflexible metabolism group’s. This indicated that the flexible metabolism participants were burning more fat than carbohydrates while sleeping.
The ability to use sleep-time RQ measurements to identify a person’s metabolic flexibility — or inflexibility — could present a new method of identifying someone’s risk factor for metabolic diseases like obesity and diabetes.
While this is not a predictor of future obesity, identifying a person’s physiological processes may help determine a person’s potential risk, and take preventative measures.
Measuring sleeping RQ values is one way to identify patients who are at a high risk of developing metabolic diseases, allowing the problem to be treated before it becomes a lifelong problem. Through this RQ analysis, researchers showed the potential of early intervention with metabolic diseases.