Trendy intermittent fasting is detrimental to the immune system and raises risk of infections

Intermittent fasting may increase the risk of developing heart disease or cancer, a study suggests. 

In a study on mice, Mount Sinai researchers found skipping breakfast caused white blood cell count to fall by up to 90 percent. These cells help fight disease, control inflammation and eliminate damaged cells from the body.

Dr Filip Swirski, an immunologist at the New York City hospital who led the study, said: ‘Because [immune cells] are so important to other diseases like heart disease or cancer, understanding how their function is controlled is critical.’

Researchers also said the study is among the first to show that skipping meals triggers a stress response in the brain that negatively affects immune cells. 

While some studies have claimed that intermittent fasting may be linked to longevity, recent research has suggested it may have the opposite effect.

Jennifer Aniston (right) and Mark Wahlberg are both fans of the intermittent fasting diet. But a study by scientists at Mount Sinai in New York has suggested fasting could raise your risk of heart disease and cancer

Intermittent fasting was one of the hottest dieting trends of the 2010s. 

The diet sees a person limit their caloric intake to either certain hours or the day – or days of the week – to lose weight and control eating habits.

Popular iterations include the 14:10 plan – where a person eats only within a 10 hour window each day and the 16:8.

Others use alternative day fasting strategies, like the 4/3 or 5/2 diets.

In both plans, a person eats normally four to five days per week, then severely restricting their food intake to 500 to 600 calories on the other two or three days.

Among celebrities who swear by the diet is Jennifer Aniston, who revealed in 2019 that she only consumes liquids in the mornings — saving her first meal until midday.

Mark Wahlberg is also a fan of the diet, limiting himself to only eating food between 12pm and 6pm every day. 

Supporters suggest the diet prompts weight loss, lowers inflammation levels and can help people live longer.

Dr Swirski said: ‘There is a growing awareness that fasting is healthy, and there is indeed abundant evidence for the benefits of fasting.

‘[However], our study provides a word of caution as it suggests that there may also be a cost to fasting that carries a health risk.

‘This is a mechanistic study delving into some of the fundamental biology relevant to fasting. The study shows that there is a conversation between the nervous and immune systems.’

In the paper, published in the journal Immunity, scientists split mice into two groups. One group received breakfast — the rodents’ largest meal of the day — while the other group went without.

Scientists drew blood from mice at the start of the study, and at four, eight and 24 hours into the experiment. 

Samples were tested for monocytes — white blood cells made in the bone marrow that fight infections, heart disease and cancer.

At the outset, all the lab rodents had the same number of these cells in their bloodstreams.

But after four hours, the fasting group saw 90 percent of these cells disappear.

There was an even further decline at eight hours.

Scans showed that the cells had migrated back to the bone marrow. Production of new monocytes in this area also diminished.

The fasted mice were denied food for 24 hours, before finally being allowed to have a meal again.

When this happened, however, the white blood cells surged back into the bloodstream and triggered inflammation.

This inflammation occurs because of an immune response to the blood cells’ return, as it is a tactic used by the body to fight off parasites and other invaders.

Further analysis revealed that when the mice were hungry, it prompted a stress response in the brain — which the researchers likened to feeling ‘hangry’, or feeling hungry and angry.

This triggered the white blood cells to move to the bone marrow, and once it was relaxed, they could return to the bloodstream.

Dr Swirski said: ‘The study shows that, on the one hand, fasting reduces the number of circulating monocytes, which one might think is a good thing, as these cells are important components of inflammation.

‘On the other hand, the reintroduction of food creates a surge of monocytes flooding back into the blood, which can be problematic.

‘Fasting therefore regulates this pool in ways that are not always beneficial to the body’s capacity to respond to a challenge such as an infection.’