This Is What Happens To The Body After Seven Days Without Food

Billions of people around the world regularly fast to lose weight or for religious reasons, yet until now the full biological implications of prolonged calorie restriction have remained poorly understood. Hungry for some proper data to get their teeth into, researchers have now analyzed the systemic changes that occur across multiple organs during long periods without food, revealing both positive and negative impacts on health.

The study authors recruited 12 healthy volunteers to take part in a seven-day fast, during which time they were allowed to drink water but could not consume any food. Participants were closely monitored throughout this period, with researchers measuring changes in around 3,000 different blood proteins on a daily basis.

Digesting their findings, the study authors report that volunteers’ bodies switched their energy sources within the first few days of the fast, and began burning stored fat rather than glucose. As a result, participants lost an average of 5.7 kilograms (12.6 pounds) across the week, and kept this weight off even after they began eating food again.

Surprisingly, however, the researchers noted no major alterations in blood protein levels for the first few days of the fast. This situation then changed dramatically after the third day, as hundreds of compounds with massive impacts on health began to fluctuate wildly.

By cross-referencing their findings with genetic studies linking these various proteins to different diseases, the study authors were able to estimate the health consequences for 212 plasma compounds that changed during fasting. 

For example, they found that abstaining from food for more than three days led to a decrease in plasma levels of switch-associated protein 70 (SWAP70). Since lower levels of this marker have been linked with a reduced risk of rheumatoid arthritis (RA), the researchers speculate that this finding “might provide at least a partial explanation for the pain relief of patients with RA during prolonged fasting.”

Also on the menu was a protein called hypoxia up-regulated 1 (HYOU1), which is associated with coronary artery disease. Over the course of the fast, levels of this compound were seen to drop, suggesting that sustained periods without food may have a beneficial impact on heart health.

At the same time, the researchers identified several negative health outcomes associated with fasting. For instance, they observed an increase in coagulation factor XI, thus potentially heightening the risk of thrombosis events. 

“For the first time, we’re able to see what’s happening on a molecular level across the body when we fast,” said study author Claudia Langenberg in a statement. “Our results provide evidence for the health benefits of fasting beyond weight loss, but these were only visible after three days of total caloric restriction – later than we previously thought.”

Summarizing the implications of this research, co-author Maik Pietzner adds that “while fasting may be beneficial for treating some conditions, often times, fasting won’t be an option to patients suffering from ill health.”

The study has been published in the journal Nature Metabolism.

The content of this article is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of qualified health providers with questions you may have regarding medical conditions.    

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