Fasting’s Unknown Health Benefits Revealed in New Study

Fasting’s Unknown Health Benefits Revealed in New Study

What happens to your body when you fast?

Fasting has been practiced for thousands of years for both medical and cultural reasons. Our hunter-gatherer ancestors were also forced to adapt to extended periods without food and, as a result, our bodies have evolved to survive and thrive through extended periods of fasting.

During fasting, our body changes its source of fuel, switching from easy access sugars to breaking down its own fat stores. However, beyond this change in fuel source, very little is known about how the body actually responds to long periods without food.

In a new study published in the journal Nature Metabolism, researchers from Queen Mary University in London and the Norwegian School of Sport Sciences followed 12 healthy volunteers over a seven-day water-only fast. The volunteers were closely monitored to track changes in the levels of various protein markers in their blood, giving a simple snapshot of the body’s response to its changing environment.

Drinking water
A stock image shows a woman drinking a glass of water. Participants in a study were asked to undergo a water fast for seven days while their blood biomarkers were measured.


As expected, the researchers observed the participants switching from glucose to fat as their major fuel source within the first two to three days of fasting. In total, the volunteers lost an average of 5.7 kilograms of both fat mass and lean mass. However, the researchers also observed distinct changes in the participants’ blood biomarkers after about three days of fasting.

Their results demonstrate that three days of fasting triggers a whole-body response. Of particular interest were changes in the proteins that make up the supportive structure for our brain cells.

“For the first time, we’re able to see what’s happening on a molecular level across the body when we fast,” Claudia Langenberg, Director of Queen Mary’s Precision Health University Research Institute (PHURI), said in a statement. “Fasting, when done safely, is an effective weight loss intervention. Popular diets that incorporate fasting—such as intermittent fasting—claim to have health benefits beyond weight loss.

“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.”

It is important to remember that, while the results were consistent across participants, the study was carried out on a very small cohort. It remains to be seen whether the results would be replicated on a larger scale.

There are also many people for whom fasting is not an option.

“While fasting may be beneficial for treating some conditions, often times, fasting won’t be an option to patients suffering from ill health,” Maik Pietzner, Health Data Modelling Chair of PHURI and co-lead of the Computational Medicine Group at the Berlin Institute of Health at Charité, said in a statement. “We hope that these findings can provide information about why fasting is beneficial in certain cases, which can then be used to develop treatments that patients are able to do.”

Anyone interested in exploring total calorie restriction should speak to a medical professional before making drastic changes to their diet.