Fasting diets may be incredibly popular at the moment but it is only in the last few years that scientists have begun to understand what happens to the human body when it is wholly deprived of food. A compelling new study by a team of Japanese researchers has offered an incredibly thorough examination into the metabolic alterations that occur in human blood during fasting, revealing a fascinating array of changes that could point to a variety of health benefits.
"Recent aging studies have shown that caloric restriction and fasting have a prolonging effect on lifespan in model animals ... but the detailed mechanism has remained a mystery," explains Takayuki Teruya, first author on the new study.
The research set out to exhaustively analyze the metabolic profile of blood samples as subjects underwent an extensive stretch of fasting. Four healthy participants were recruited and subjected to a long fast, with blood samples taken at three points in the process: 10, 34 and 58 hours after commencing fasting. Unlike prior research, which often focused on specific metabolic biomarkers, this study was non-targeted with a goal of uncovering previously unidentified metabolic effects from fasting.
"Contrary to the original expectation," says Teruya, "it turned out that fasting induced metabolic activation rather actively."
The researchers identified 44 different blood-based metabolites significantly increasing in abundance after 58 hours of fasting, including 30 that have never before been connected to the practice. Alongside known markers signaling the body is moving to utilizing alternative energy stores, such as butyrates and branched-chain amino acids, an interesting increase in anti-oxidant metabolites was found. It is suggested this could be an evolutionary defense against the oxidative stress put on the body during fasting.
Other previously unidentified metabolites revealed in the study signaled enhanced mitochondrial activity. This discovery adds weight to a compelling Harvard study from last year that suggested fasting can increase longevity and promote healthy aging by kickstarting youthful plasticity in mitochondrial networks.
Interestingly, three specific metabolites known to be associated with aging and longevity – leucine, isoleucine, and ophthalmic acid – all increased in levels after fasting. Prior study by the same research team revealed these specific metabolites decrease with age and are found in notably low levels in the elderly.
"These are very important metabolites for maintenance of muscle and antioxidant activity, respectively," adds Teruya. "This result suggests the possibility of a rejuvenating effect by fasting, which was not known until now."
One of the biggest limitations in this particular study was the small sample size. Although the ultimate increases in metabolites were consistent across all four subjects, how quickly those metabolites peaked did vary from person to person. The researchers note that further work in more subjects will hopefully resolve any questions over individual metabolic respond patterns.
As well as helping understand exactly what occurs in a human body when it is subjected to fasting, the researchers are keen to explore how to trigger certain metabolic changes without forcing a person to fast. A better understanding of the mechanisms underpinning the anti-aging qualities of fasting, for example, could hopefully lead to a variety of different life extension treatments.
"It might be possible to verify the anti-aging effect from various viewpoints by developing exercise programs or drugs capable of causing the metabolic reaction similar to fasting," says Teruya.
The new study was published in the journal Scientific Reports.
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