Fasting for three days can lead to weight loss but going without food for a week carries no significant further health benefits, according to a study.
Scientists at Queen Mary University of London monitored 12 healthy volunteers taking part in a week-long water fast and tracked changes in the levels of 3,000 proteins in their blood.
They observed that one in three of the proteins measured changed “significantly” in all major organs, including changes in proteins that make up supportive structures in the brain.
The volunteers lost an average of 5.7kg of both fat mass and lean mass during the fast. After three days of eating after the fast, the weight stayed off but the health benefits of fasting only extended to three days of calorie restriction, the study found.
Maik Pietzner, Health Data Chair of Queen Mary’s Precision Healthcare University Research Institute (PHURI), said: “While fasting may be beneficial for treating some conditions, often times, 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.”
Intermittent fasting has become a popular weight loss trend in recent years and scientists argue it carries a number of health benefits, including improved cognitive function and reduced risk of diabetes.
Last month, Prime Minister Rishi Sunak revealed that he fasts for 36 hours a week and consumes nothing but black coffee, tea and water between 5pm every Sunday until 5am on Tuesday morning.
There are varying types of fasting, some including reducing calorie intake significantly on certain days, or going without food entirely on some.
Those who want to try it are advised to speak to medics first, and it is not advised for people with a history of disordered eating or who are pregnant.
Claudia Langenberg, director of Queen Mary PHURI, said: “For the first time, we're able to see what's happening on a molecular level across the body when we fast. 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.”
