Three new studies published recently in the journal Cell have investigated the effects of fasting on different immune system mechanisms. The research reveals significantly different immune responses can be generated depending on the type of fasting studied, suggesting not all fasting diets are created equal.
It’s reasonable to be a little confused over the variety of fashionable fasting diets these days. From extreme multi-day, water-only fasts, to time-restricted intermittent feeding strategies such as only eating across a six-hour period every day, it is clear these diets have notable metabolic effects on the human body. But it is only recently that scientists have begun to explore the differences between these fasting cycles, and in particular the effect of these dietary strategies on the immune system.
Across three newly published studies, scientists have shown how certain fasting models can result in potent changes to immune system mechanisms. However, each diet can result in differing, and even opposite, immune effects, suggesting fasting diets need more accurate definitions in future research.
One study examined the effects of calorie restriction on the activity of memory T cells in mice. The research discovered enhanced T cell protection against infections and tumors when an animal’s caloric intake was reduced by 50 percent.
Another study looked at the effect of complete short-term fasting on monocytes, a pro-inflammatory immune cell, in both human and mouse models. The study found a short-stretch of fasting in both humans and mouse models resulted in less circulating monocytes and lowered monocyte inflammatory activity.
This, of course, is a useful observation if applied to someone suffering from a chronic inflammatory condition, but how does this immune system impairment affect a healthy body’s ability to heal wounds or fight off an infection?
The second study examined this question by comparing the immune effect of short-term fasting to longer term starvation on a mouse’s ability to fight off infection. While short-term fasting (less than 24 hours) did not compromise an animal’s ability to heal a wound or fight off infection, longer fasts did indeed begin to cause problems. When starved for 48 hours before skin injury or infection, significant immune response impairments were noticed.
The final study also investigated the effect of complete fasting on immune response in mouse models. This third study focused on gut immune response after fasting in young, healthy mice. Here the researchers were interested in understanding whether repeated stretches of fasting had detrimental effects on gut immune response in otherwise healthy animals.
Juvenile mice displayed significant immune system impairments after repeated 36-hour fasting stretches. In these young mice fasting seemed to have a detrimental effect on their immune system, exacerbating metabolic dysfunction and promoting allergic responses.
“… we found that food intake secures the integrity and function of the gut mucosal immune system through nutritional signaling,” write the researchers in the conclusion to their study. “Nutritional deprivation impairs mucosal immunity, leading to immune barrier dysfunction and excessive allergic response.”
What all this research means is that fasting diets may not be beneficial for everyone, and different kinds of fasting can result in drastically different kinds of immune system responses. In an editorial response to these three studies, researchers Roberta Buono and Valter Longo suggest the differing results demand more precise future research and clarity over different fasting strategy definitions.
“…the three new studies demonstrate the ability of different forms of fasting, as well as different lengths of fasting, to cause potent but distinct and at times opposite effects on the levels and function of various immune cell types, thus underlining the need to replace terms like fasting, or intermittent fasting, with those that describe the type and length of the fasting method such as a 24 h alternate-day fasting (12 H ADF), a 12 h time-restricted feeding (12 H TRF), or a 5-day fasting- mimicking diet (5-day FMD),” write Buono and Longo.
The three new studies are published in the journal Cell.
Sources: National Institutes of Health, Mount Sinai, Scimex