Occasional fasting may not only help people lose weight but also boost their metabolic activity, generate antioxidants, and reverse some effects of ageing, a study claims.
Scientists at the Okinawa Institute of Science and Technology (OIST) and Kyoto University in Japan identified 30 previously-unreported substances whose quantity increases during fasting and indicate a variety of health benefits.
"We have been researching ageing and metabolism for many years and decided to search for unknown health effects in human fasting," said Takayuki Teruya, first author of the paper published in the journal Scientific Reports.
"Contrary to the original expectation, it turned out that fasting induced metabolic activation rather actively," said Teruya.
The study presents an analysis of whole human blood, plasma, and red blood cells drawn from four fasting individuals. The researchers monitored changing levels of metabolites -- substances formed during the chemical processes that grant organisms energy and allow them to grow.
The results revealed 44 metabolites, including 30 that were previously unrecognised, that increased universally among subjects between 1.5- to 60-fold within just 58 hours of fasting.
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In previous research, researchers identified various metabolites whose quantities decline with age, including three known as leucine, isoleucine, and ophthalmic acid.
In fasting individuals, these metabolites increase in level, suggesting a mechanism by which fasting could help increase longevity.
"These are very important metabolites for maintenance of muscle and antioxidant activity, respectively," said Teruya.
"This result suggests the possibility of a rejuvenating effect by fasting, which was not known until now," he said.
The human body tends to utilise carbohydrates for quick energy -- when they are available. When starved of carbs, the body begins looting its alternate energy stores.
The act of "energy substitution" leaves a trail of evidence, namely metabolites known as butyrates, carnitines, and branched-chain amino acids.
These well-known markers of energy substitution have been shown to accumulate during fasting.
However, fasting appears to elicit effects far beyond energy substitution.
In their comprehensive analysis of human blood, the researchers noted both established fasting markers and many more.
For example, they found a global increase in substances produced by the citric acid cycle, a process by which organisms release energy stored in the chemical bonds of carbohydrates, proteins and lipids.
The marked increase suggests that, during fasting, the tiny powerhouses running every cell are thrown into overdrive.
Fasting also appeared to enhance the metabolism of purine and pyrimidine, chemical substances which play key roles in gene expression and protein synthesis.
The finding suggests fasting may reprogramme which proteins cells build at what time, thus altering their function.
The change may promote homeostasis in cells, or serve to edit their gene expression in response to environmental influences.
The findings expand on established ideas of what fasting could do for human health. The next step would be to replicate these results in a larger study, or investigate how the metabolic changes might be triggered by other means.