Research identifies the body’s reaction to seven days fasting

Adaptive proteomic changes in humans during 7-day caloric restriction.


A new study in Nature Metabolism, led by researchers from Queen Mary’s Precision Healthcare University Research Institute and the Norwegian School of Sports Sciences, highlights what occurs in the body during prolonged periods without food. This research gives importance to potential treatments, especially for those unable to fast due to medical reasons. 

Fasting, practiced in various cultures and religions, has historically been used to manage conditions like epilepsy and rheumatoid arthritis. While fasting is often associated with weight loss, its broader health benefits have been suggested. However, until now, little was understood about the body’s responses during fasting beyond the shift from using consumed calories to stored fat for energy.

New methods for measuring thousands of proteins in our blood have enabled researchers to study how our bodies change during fasting.

In a study, 12 healthy volunteers fasted for seven days, drinking only water. Researchers closely watched these volunteers daily to see how the levels of about 3,000 proteins in their blood changed before, during, and after the fast. By figuring out which proteins are involved in the body’s response, the researchers could guess what health effects prolonged fasting might have by combining this data with genetic information from extensive studies.

During fasting, the body uses fat instead of glucose for energy, typically within the first few days. Volunteers lost around 5.7 kg of fat and lean mass during a seven-day fast. After eating again for three days, the weight stayed off, with lean mass mostly restored but fat mass remaining lower.

After three days of fasting, the researchers noticed significant changes in protein levels throughout the body, showing a complete response to calorie restriction. About one in three measured proteins were changed significantly across substantial organs. These changes were similar among volunteers. However, there were unique fasting signatures beyond weight loss, such as alterations in proteins supporting brain neurons.

Claudia Langenberg, Director of the Precision Health University Research Institute (PHURI), explained that “their study unveils what happens in the body at a molecular level during fasting. If done safely, fasting can help with weight loss, and diets like intermittent fasting claim additional health benefits. However, their research found evidence of these benefits only after three days of total caloric restriction, which was later than previously thought.”

Maik Pietzner, Health Data Chair of PHURI and co-lead of the Computational Medicine Group at Berlin Institute of Health at Charité, highlighted that their findings support the traditional use of fasting for specific conditions. However, fasting might not always be suitable for patients with health issues. They hope these findings can guide the development of treatments based on the benefits of fasting, which could be more comfortable to patients.

This study helps us learn more about how different body parts react when people fast for a long time. By figuring out the tiny changes in our body during fasting, we can look into using fasting to help treat different health problems. Also, we need to do more research to ensure fasting is done safely and get the most health benefits out of it.

Journal reference:

  1. Pietzner, M., Uluvar, B., Kolnes, K.J. et al. Systemic proteome adaptions to 7-day complete caloric restriction in humans. Nature Metabolism. DOI: 10.1038/s42255-024-01008-9.
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