A STUDY made by Kyoto University researchers suggests that fasting leads to fuel substitution, antioxidation, increased mitochondrial activation and altered signal transduction.
Going without food may boost human metabolic activity, generate antioxidants, and help reverse some effects of aging. Scientists at the Okinawa Institute of Science and Technology Graduate University (OIST) and Kyoto University identified 30 previously-unreported substances whose quantity increases during fasting and indicate a variety of health benefits.
In the study, 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 unrecognized, that increased universally among subjects between 1.5- to 60-fold within just 58 hours of fasting.
"These are very important metabolites for maintenance of muscle and antioxidant activity, respectively," said Dr. Takayuki Teruya of OIST.
According to Dr. Teruya, the human body tends to utilize carbohydrates for quick energy -- when they're 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.
But 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. When metabolized, purine and pyrimidine also boost the body's production of antioxidants. Several antioxidants, such as ergothioneine and carnosine, were found to increase significantly over the 58-hour study period.
Antioxidants serve to protect cells from free radicals produced during metabolism. Products of a metabolic pathway called the "pentose phosphate pathway" also stay the harmful effects of oxidation, and were similarly seen to increase during fasting, but only in plasma.
The authors suggest that these antioxidative effects may stand as the body's principal response to fasting, as starvation can foster a dangerously oxidative internal environment. Their exploratory study provides the first evidence of antioxidants as a fasting marker. In addition, the study introduces the novel notion that fasting might boost production of several age-related metabolites, abundant in young people, but depleted in old.
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.
"People are interested in whether human beings can enjoy the effects of prevention of metabolic diseases and prolonging life span by fasting or caloric restriction, as with model animals," said Teruya. "Understanding the metabolic changes caused by fasting is expected to give us wisdom for maintaining health."