Researchers at the University of California (UC), Irvine recently discovered that the circadian clocks of the liver and skeletal muscles are altered whenever a person fasts. The organ and muscles adjust their metabolism in response to the reduced consumption of food and access to energy.
Published in the science journal Cell Reports, the discovery of a connection between fasting and the circadian clocks of important parts of the body could be used to further enhance health. It may be possible that fasting could offer protection against symptoms and diseases that are connected to the aging process. (Related: Here’s what the research says about intermittent fasting.)
Fasting could adjust the body's natural clock
As its name implies, the circadian clock naturally keeps track of the time for the body and its organs. These time-keeping abilities allow the body to sustain homeostasis, the state of steady internal conditions in a living being.
Earlier studies have shown that food can affect the circadian clock in peripheral tissues. These tissues include the skin, lungs, and other mucosal tissue that form the lining of various cavities in the body and the external surface of the organs.
However, those studies were unable to determine how the exact opposite can affect the function of the circadian clock. But if the lack of food – such as the condition deliberately induced through fasting – could indeed affect the body's natural internal clock, it could by extension affect the entire body.
"We discovered fasting influences the circadian clock and fasting-driven cellular responses, which together work to achieve fasting-specific temporal gene regulation," said UC Irvine researcher Paolo Sassone-Corsi, the lead author of the study. "Skeletal muscle, for example, appears to be twice as responsive to fasting as the liver."
Sassone-Corsi was the one who discovered the circadian rhythm-metabolism link more than a decade ago. He found the metabolic pathways that circadian proteins used to measure energy levels in cells.
For their study, he and his research team set up an animal model using standard lab mice. The animals underwent fasting periods that lasted for 24 hours while researchers evaluated important characteristics. They measured the amount of oxygen consumed by metabolism (VO2), the respiratory exchange ratio (RER) between the amount of carbon dioxide created by metabolism and the amount of oxygen, and the amount of energy used up by the animal.
A fasting period makes the body more efficient at metabolizing food
During the experiment, the UC Irvine researchers reported that the fasting mice displayed reduced levels of VO2, RER, and energy expenditure. These levels were restored to normal once the animals had been fed.
The researchers drew parallels between these results and those in related trials involving human participants. In those studies, humans also reduced the amount of resources they expended during the fast, and their bodies quickly recovered once normal amounts of food became available again.
Based on their findings, the researchers theorized that fasting changes the level of gene functions connected to metabolic processes. Furthermore, a period of fasting could place the genome into a permissive state in anticipation of incoming food. This would start a new cycle of gene expression.
"In other words, fasting is able to essentially reprogram a variety of cellular responses," Sassone-Corsi explained. "Therefore, optimal fasting in a timed manner would be strategic to positively affect cellular functions and ultimately benefiting health and protecting against aging-associated diseases."
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