The pundits are all over the 5:2 diet (one of the more famous versions of an intermittent fasting diet) because fasting, they say, can lower your immune system and lead to infections. Here’s a typical post:
In an article for Headlines & Global News titled Myth Surrounding ‘5:2’ Diet Busted, Researchers Say it Might Weaken Immunity, the author starts with this:
People following ‘Intermittent Fasting’ or ‘5:2′ diet have weakened immune systems, a new research shows.
Another from the University Herald titled Fast Diet Weakens Immune System and Ability to Fight Disease starts out thusly:
“Intermittent Fasting or 5:2 diet” affects the nervous system and increases people’s vulnerability to infection, according to a University of Bath study.
These and many other stories seemed to feed off of each other and all come to similar conclusions, namely that intermittent fasting weakens the human immune system. But all of these articles are based on a study that didn’t have to do with humans and didn’t have to do with fasting.
The actual study, titled Hormesis Results in Trade-off with Immunity, is a study of flies conducted at the University of Bath. Hormesis describes the surprising extra fitness that results with low doses of certain stressors such as heat, fasting or toxins. In this study, the flies were coated with a dead fungal toxin that stressed them. The results showed that the treated flies lived longer and had more children. However, there was an interesting loss of immune function that left the flies more vulnerable to doses of live fungus. The authors of the study conclude:
It seems quite plausible that in healthy patients, we could employ our natural life-history responses to environmental cues [such as fasting — Ed.] to further improve their health. However, the consequences of hormetic treatments for infected patients could be dire.
How did the researchers connect fungus-coated flies to human fasting? Because a similar set of genes in both humans and flies seem to be involved in hormesis. So is this the death knell for the 5:2 diet or fasting in general? Hardly. But it indicates that some care should be taken before undertaking it. If you are at risk for infection, or if your immune system is already compromised, you might think twice. Especially if you’re a fly.