New Study Shows What Happens Inside the Body During Seven Days of Fasting - Video

A seven-day fast can trigger molecular changes across the body, with many notable effects appearing only after about three days without calories, according to a study published in Nature Metabolism.

Researchers from Queen Mary University of London and the Norwegian School of Sports Sciences studied 12 volunteers who completed seven days of fasting. Blood samples were collected before, during and after the fast, allowing researchers to track changes in about 3,000 proteins.

Participants shifted from using glucose towards stored fat as an energy source during the first two to three days. They lost an average of 5.7 kilograms, including both fat and lean mass.

However, the most substantial changes appeared around day three. About one-third of the proteins measured changed significantly during the fasting period, with alterations involving multiple organs and biological systems.

Some changes were linked to processes beyond energy metabolism and could not be explained by weight loss alone. Researchers identified changes in proteins associated with neuronal structures, suggesting that prolonged fasting may influence processes involving the brain and nervous system.

After participants resumed eating, most of the lost lean mass returned within three days, while some reduction in fat mass remained.

The researchers said the findings provide evidence that fasting may have biological effects extending beyond weight reduction. However, the study does not establish that these changes are beneficial or translate into improved health outcomes.

Importantly, the findings relate to prolonged, complete calorie restriction and should not be assumed to apply to shorter fasting patterns such as intermittent fasting.

The study provides a molecular map of how the body adapts to fasting. Further research is needed to determine which changes are beneficial and whether fasting-related pathways can eventually be targeted through treatments without requiring prolonged food restriction.

REFERENCE: Maik Pietzner et al.; Systemic proteome adaptions to 7-day complete caloric restriction in humans. Nature Metabolism, 2024; 6 (4): 764 DOI: 10.1038/s42255-024-01008-9