The more health conscious among us will be familiar with the 5:2 diet, otherwise known as intermittent fasting. Similar to the alternate-day diet and the 80:20 diets favoured by A-listers such as supermodel Miranda Kerr, the 5:2 plan has been attributed with a range of health benefits.
But now fasters may want to up their game, as a new study has found that fasting for two days or more can help to kick-start the immune system, producing new white blood cells, which fight off infection.
Starving the body, US researchers at the University of Southern California say, encourages the replacement of old and damaged cells.
A new study shows that fasting for three days reboots the immune system
Valter Longo, the university's longevity expert, explains: "When you starve, the system tries to save energy, and one of the things it can do to save energy is to recycle a lot of the immune cells that are not needed, especially those that may be damaged."
His team found fasting for two to four days every six months forced the body into survival mode, using up stores of fat and sugar and breaking down old cells.
"The body then sent a signal telling stem cells to regenerate and 'rebuild the entire system,'" he said.
So, what does a three-day fast entail, exactly?
In a nutshell, it means drinking nothing but water for 72 hours. No solid food or other liquids that contain nutrition, such as juice and milk, are allowed. Mineral water is good, as is boiled and cooled water, while slightly warm water also aids the cleansing process.
If that sounds too much like hard work, there is another option. According to the researcher, a "mimicking" fast diet of 750-1050 calories per day for at least four or five days is sufficient to kick the body into a regenerative state.
"Any fasting is better than nothing," he told The Daily Beast, "[but] 4 to 5 days of fasting are necessary to maximize its effects".
It's important to note that the fast "must be done under medical supervision and preferably in a clinic".
Scientists behind the study say that those with damaged immune systems, such as cancer patients on chemotherapy, would benefit the most.
"With a system heavily damaged by chemotherapy or ageing, fasting cycles can generate, literally, a new immune system," Professor Longo said.
Fasting is not recommended if you are pregnant or are on medication for diabetes. Consult your GP before embarking on fasting or a diet.