What Happens to Your Body When You Fast for Seven Days

Topic: Health

Scientists studied how 12 healthy people's bodies changed after a seven-day fast. They found that the body starts to adapt and change in many ways, including how it uses energy and what proteins are produced.

Going without food for several days does more than just make your body burn stored fat. Research published in 2024 showed that prolonged fasting causes widespread changes across multiple organs in our bodies.

The study, led by scientists from Queen Mary University of London's Precision Healthcare University Research Institute and the Norwegian School of Sports Sciences, followed 12 healthy volunteers who completed a seven-day water-only fast. The researchers measured changes in about 3,000 proteins in their blood before, during, and after the fast.

They found that as expected, the body started to shift away from using glucose (a type of sugar) for energy and towards stored fat within the first two or three days without food. During this time, participants lost an average of 5.7 kilograms, with some weight loss coming from muscle mass and other tissues.

However, the most striking finding was that after approximately three days of fasting, the body underwent a major shift in how it uses energy and produces proteins. This change remained even after participants resumed eating.

Why It Matters

This study can help us understand how our bodies respond to fasting, which is important for people who fast for cultural, religious, or medical reasons. It could also lead to new treatments that mimic the benefits of fasting without requiring people to go without food for extended periods.

Key Facts

• 12 healthy volunteers completed a seven-day water-only fast as part of the study.
• The researchers measured changes in about 3,000 proteins in their blood before, during, and after the fast.
• Participants lost an average of 5.7 kilograms during the fast, with some weight loss coming from muscle mass and other tissues.
• A major shift in how the body uses energy and produces proteins occurred around day three of the fast.
• The study was published in Nature Metabolism in 2024.

Key Terms

Glucose

a type of sugar that our bodies use for energy

Proteins

molecules that carry out many jobs in the body, including building tissues and controlling chemical reactions

Implications

This study can help us understand how our bodies respond to fasting, which is important for people who fast for cultural, religious, or medical reasons. It could also lead to new treatments that mimic the benefits of fasting without requiring people to go without food for extended periods.