What physiological changes occur during a fast?
Fasting has been a part of human culture and medicine for thousands of years. Our bodies have evolved to endure and thrive during prolonged fasts because our hunter-gatherer ancestors had to adjust to going without food for extended periods of time.
Our body uses its own fat reserves to generate energy during a fast instead of readily available glucose. Beyond this shift in fuel source, however, very little is understood about the actual reactions of the body during prolonged fasts.
Researchers from Queen Mary University in London and the Norwegian School of Sport Sciences monitored 12 healthy volunteers for a seven-day water-only fast as part of a new study that was published in the journal Nature Metabolism. The subjects’ blood levels of different protein markers were continuously tracked, providing a basic snapshot of the body’s reaction to its shifting surroundings.
As predicted, during the first two to three days of fasting, the subjects’ primary fuel source changed from glucose to fat, according to the researchers. The average weight loss for the subjects was 5.7 kg less in lean and fat mass overall. But, following roughly three days of fasting, the participants’ blood biomarkers also showed noticeable alterations, according to the researchers.
Their findings show that a whole-body reaction is triggered by a three-day fast. Changes in the proteins that support the structure of our brain cells were of special interest.
“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 crucial to keep in mind that the study was conducted on a relatively small cohort, even if the results were consistent across participants. Whether the outcomes would be repeated on a bigger scale is still to be determined.
Maik Pietzner, the co-lead of the Computational Medicine Group at the Berlin Institute of Health at Charité and the Health Data Modelling Chair of PHURI, stated in a statement that “while fasting may be beneficial for treating some conditions, fasting won’t be an option to patients suffering from ill health.” “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.”
Before making significant dietary changes, anyone interested in learning more about complete calorie restriction should consult a physician.
