A study examining what happens during prolonged fasting found that the body’s most significant molecular changes may not begin until approximately three days without food. The findings, published in Nature Metabolism, suggest that fasting may influence health in ways that extend beyond weight loss.
Researchers from Queen Mary University of London and the Norwegian School of Sports Sciences followed 12 healthy volunteers who completed a seven-day water-only fast. The team measured changes in approximately 3,000 proteins in participants’ blood before, during, and after the fasting period.
As expected, the body shifted from glucose to stored fat as its primary energy source within the first two to three days. Participants lost an average of 5.7 kilograms, from both fat mass and lean mass. Three days after resuming eating, most lost lean mass had returned whilst the reduction in fat mass remained.
The most notable finding emerged after approximately three days of fasting, when researchers detected distinct changes in protein levels throughout the body. About one third of all proteins measured changed significantly during the fasting period, with effects linked to all major organs. These changes appeared to represent a coordinated whole-body response rather than simply altered energy metabolism.
The researchers also detected biological signatures that could not be explained by weight loss alone, including changes in proteins associated with neuronal structural support in the brain.
The findings could eventually help develop treatments that reproduce some of fasting’s effects for patients who cannot safely undergo prolonged fasting. However, the results do not indicate that shorter fasting schedules, such as intermittent fasting, necessarily produce the same effects.
Source: Pietzner M et al. Systemic proteome adaptions to 7-day complete caloric restriction in humans. Nature Metabolism (2024). DOI: 10.1038/s42255-024-01008-9
