Intermittent fasting – where you regularly refrain from eating for most of a day or two – has shown mixed results for losing weight, with some research showing that it’s as good as, but no better than, old-fashioned counting calories.

However, there’s a theory that fasting can activate cellular mechanisms that help boost immune function and reduce inflammation associated with chronic disease.

Since the pandemic, this idea has spawned a growing body of evidence that suggests reducing inflammation by fasting brings a lower risk of severe illness from COVID-19.

Well the evidence has firmed up

A fascinating new study of COVID-19 patients in Utah found those “who practiced regular water-only intermittent fasting had lower risk of hospitalisation or dying due to the virus than patients who did not”.

It appears that the participants, at least a good number of them, were Mormons who engage in intermittent fasting once a month for religious reasons by going without food or drink for two consecutive meals on the first Sunday of every month.

But it’s important to note that these study participants had practised fasting on average for 40 years.

This suggests you don’t need to fast often to get the protective benefits – but you may need to keep at it for a long time.

A preventative therapy?

The authors conclude that fasting “may be a complementary therapy to vaccination (but not a substitution for vaccination) that could provide immune support and hyperinflammation control during and beyond the pandemic”.

Lead author Dr Benjamin Horne, director of cardiovascular and genetic epidemiology at the Intermountain Heart Institute in Sat Lake City, said in a prepared statement:

“Intermittent fasting has already shown to lower inflammation and improve cardiovascular health. In this study, we’re finding additional benefits when it comes to battling an infection of COVID-19 in patients who have been fasting for decades.”

In the study, researchers identified patients enrolled in the INSPIRE registry, a voluntary health registry at Intermountain Healthcare, who had also tested positive for SARS-CoV-2 between March 2020 and February 2021 – before vaccines were widely available.

This was a small study in which 205 patients had tested positive for the virus – with 73 of those reporting that they regularly fasted at least once a month.

“Intermittent fasting was not associated with whether or not someone tested positive COVID-19, but it was associated with lower severity once patients had tested positive for it,” Dr Horne said.

 How might fasting work?

In 2019, before COVID-19 was known to anybody, Mount Sinai researchers published a study that found fasting reduced inflammation and improved chronic inflammatory diseases without affecting the immune system’s response to acute infections.

The authors noted that while acute inflammation was a normal immune response to infections, chronic inflammation had serious consequences for people with heart disease, diabetes, cancer, multiple sclerosis, and inflammatory bowel diseases.

It’s also worth noting, that the simple act of eating anything provokes an immune response.

Of course, none of that was new. What the researchers were looking for was an explanation for how reducing calories controlled inflammation.

And they found it

As senior author Dr Miriam Merad, Director of the Precision Immunology Institute at the Icahn School of Medicine at Mount Sinai described it:

Intermittent fasting reduced the release of pro-inflammatory cells called ‘monocytes’ in blood circulation.

Further, during periods of fasting, these cells went into ‘sleep mode’ and were less inflammatory than monocytes found in those who were fed.

“Monocytes are highly inflammatory immune cells that can cause serious tissue damage, and the population has seen an increasing amount in their blood circulation as a result of eating habits that humans have acquired in recent centuries,” said Dr Merad.

She and her colleagues concluded there was enormous potential in investigating the anti-inflammatory effects of fasting – and suggested more research was needed.

Five months later, the world was taken over by a disease in which hyper-inflammation was a key cause of serious illness and death.