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Fasting – the voluntary abstinence from food and drink – triggers the activation of a vast array of biochemical processes and signaling pathways that optimize human performance and physiological function, possibly slowing the processes of aging and disease. A recent study found that fasting induced profound, diverse increases in the metabolites present in blood.

Metabolites are substances produced in an organism, cell, biological fluid, or tissue during metabolism. The collection of these metabolites in their entirety is referred to as the metabolome. Metabolomics is an emerging field of study involving the identification and quantification of the metabolome at a specific time point to create a metabolic profile that provides information about the body’s physiological state. Previous research has identified 126 distinct metabolites in human blood.

The authors of the study drew blood samples from four healthy, young (average age, xx years) non-obese volunteers at three intervals (10, 34, and 58 hours) during a period of fasting. They analyzed the participants' metabolomic profiles in whole blood, plasma, and red blood cells and identified changes (increases or decreases) in the metabolites. Their analysis revealed that the participants' blood glucose levels remained within the normal range (70 to 80 mg/dL) and ATP levels were consistent throughout the fasting period. Levels of most of the previously identified metabolites remained unchanged during the fast, but 44 metabolites increased, and two decreased.

Those that increased included butyrate, branched-chain amino acids, carnitines, organic acids, coenzymes, pyrimidines, purines, antioxidants, and molecules associated with the pentose phosphate pathway. These compounds support multiple metabolic pathways and biological processes, including gluconeogenesis (the production of glucose from ketones, glycerol, and amino acids), protein synthesis, and mitochondrial activity, among others. The compounds that decreased were aspartate (an amino acid) and gluconate (a glucose derivative).

These findings suggest that fasting induces a metabolically active state in healthy, young adults. However, this was a very small study, so larger studies are needed to confirm the findings.

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