I am one of the self-motivated activists who run some groups to answer various misconceptions about science and try to fight against ignorance, pseudo-sciences and blind faiths. I was recently asked by several participants about fasting as a "remedy" for infections. Many Ayurvedic practitioners make this claim and make vague reference to research on autophagy. Unfortunately, millions of people fall victim to such fallacious claims.

Here are some references about claims: 1."... Patients down with common fever are almost always advised to fast for one day, so that the body toxins get washed out for good; this opens up a healthy passage for the bed-ridden to be treated from fever as soon as possible."

[Source: http://www.ayurvedatreatments.co.in/ayurvedatreatments/index.php/399-ayurveda-treatment-for-all-common-fever] 2."When you are of the belief that you have been infected by amoebiasis or have an over growth of candidas stop consuming food and water until your prana starts flowing to pingala and your hunger is back in fiery shape."

[Source: https://ancienthealingsecrets.wordpress.com/2013/12/12/dry-fasting-for-candidiasis-amoebiasis-and-other-infection-or-parasitic-attacks/]

These are just two examples. There are many such sites with millions of followers. Ayurveda is a recognized medical practice in India.

But, I'm not convinced about such claims because research only shows that "intermittent" fasting boost autophagy which in turn improves immune system in general. Autophagy is a catabolic process where a cell "eats itself" and recycles the intracellular constituents. This also happens when cell naturally dies. Intermittent starving is only one of the ways autophagy gets induced and studies only show that autophagy induced by intermittent starving boosts immune system. Moreover, research also shows that some cancer cells also induce autophagy and rely on that for survival. In such cases, inhibition of autophagy is a actually a good strategy.

However, I don't think any of these imply "recovery" when you are already infected or when infection is well established. It's dangerously fallacious logic and it's like saying, "Your heart becomes healthy when you run regularly. So, start running when you have an heart attack".

I simply want a valid reference that says fasting is actually beneficial even when one is already infected. To me there is a very good chance that opposite may be true.

  • 2
    A great question! Welcome to health SE :-).
    – Lucky
    Commented Oct 5, 2016 at 17:50

1 Answer 1


This sounds like dream come true for 'alternative medicine': Water-Only Fasting Can Help The Body To Fight Off Disease – And Can Have The Most Profound Health Benefits Too:

A recent news item caught my attention – it concerns the therapeutic value of fasting. Researchers at the University of Southern California presented a study that explained that refraining from food for as little as two days can regenerate the immune system, and in addition, fasting for two to four days helps the body to fight infection and “flips a regenerative switch” that triggers stem cell-based regeneration of new white blood cells, thereby renewing the body’s defense system. During the fast, the body gets rid of the parts of the system that might be damaged or old, the inefficient parts. The scientists believe that even if you start with a system heavily damaged by chemotherapy or aging, fasting cycles can generate an entirely new immune system. In a small pilot clinical trial researchers found that fasting for a 72-hour period prior to chemotherapy protected patients against toxicity. Fasting also affects the levels of a substance in our bodies called IGF -1 and in reducing this it diminishes tumour growth and the risk of developing cancers.

So, how does water-only fasting actually work? What is going on in the body?

Water-only fasting – as the name suggests is where you only drink water and take no food whatsoever and, most importantly, you must take complete bed rest. The truly therapeutic part of the fast does not actually begin until the second or third day: the reason for this is that during the first 24 - 48 hours after starting a water fast, the body is still burning off circulating blood sugar and also sugar stored in the muscles and liver in the form of glycogen. Once the first two to three days of the fast are over, your body then begins to burn fat tissue for fuel. Next, molecules named ketones begin circulating in the blood. Ketones suppress hunger and this is why fasting is not a difficult process – once you are over the first few days.

Many people don’t understand the process of ketosis correctly and fear that this could damage the kidney and brain, possibly leading to loss of consciousness and even more dire consequences. However, a group of ‘hygienic physicians’ as doctors working in this field are known (and which includes Dr Sabatino as one of the leaders in the field), have supervised many thousands of fasts over the past 50 years, and have shown these concerns to be unfounded. In fact, when fasting is undertaken in a supportive environment, with the supervising practitioner ensuring proper hydration, and total resting conditions, kidney and heart function often dramatically improve as weight and blood pressure drop. There is often a dramatic improvement in the acuity of special senses, vision, hearing etc. People wearing glasses will sometimes remark how they experience moments of absolutely perfect eyesight without their glasses.

"Researchers found out": without a link to the original study, not even a date on the article cited above, that is very poor reporting and avoids being checked for accuracy. A very poor practice. Apart from some valid information, and relying on unsourced and probably preliminary scientific evidence, and using impressive sounding abbreviations, there is also the corresponding bull**** mixed under (e.g. "fasting cycles can generate an entirely new immune system").

But are there studies that might confirm these alleged findings? A more reliable source for this claim is presented in a very accessible article here:

Feed Or Starve A Sickness? It Depends On The Infection: To investigate how loss of appetite might affect the immune system in sick animals, researchers infected some mice with the bacteria Listeria (a common cause of food poisoning), and some with the influenza virus.
When the mice were force fed, those with bacterial infections died—but those with viral infections were more likely to survive. The researchers determined that glucose in food was responsible for these divergent fates (rather than proteins or fats). When the team used drugs to block the mice from using glucose, the mice infected with bacteria survived, while their virus-ridden peers died.
Viral and bacterial infections induce different types of immune responses. So our metabolism might require different fuels to prevent inflammation from damaging the body. During a viral infection, glucose seems to be key. But during a bacterial infection, fasting benefited the mice by allowing them to use ketones, a different fuel that is produced when fat is broken down.

That indicates an important finding that might have very profound effects in the future. But the cited article is sensible enough to also state clearly:

But it’s definitely too soon for these findings to translate into advice about how sick people should eat. This study focused on one strain of mice in a lab setting and only a couple of forms of infection. “It remains to be seen how these results apply to critical illness in humans,” Medzhitov and his coauthors wrote.

The original research article is published here: Opposing Effects of Fasting Metabolism on Tissue Tolerance in Bacterial and Viral Inflammation (2016).

To repeat, in there is the important caveat to note:

One limitation of this study (common to most animal studies) is that it was performed on a single mouse strain (C57BL/6J) in one mouse facility. Thus, the roles of genetic background and facility-specific environment remain unknown. In addition, there are many caveats with extrapolating data on organismal biology from studies in unnatural settings of animal facilities. […] Finally, it remains to be seen how these results apply to critical illness in humans.

Further studies at least confirm that there are some interesting changes related to the modulation of immune system responses while fasting:

Fasting metabolism modulates the interleukin-12/interleukin-10 cytokine axis (2017): […] Growing evidence indicates that metabolic processes impact both, innate and adaptive immunity. […] In conclusion, we showed that fasting metabolism modulates the IL-12/IL-10 cytokine balance, establishing novel targets for metabolism-based immune-modulation.

So, sadly, we still do not know for sure.

General problems to simply saying "it works" are summarised here:

Calorie restriction in rodents: Caveats to consider (2017): The calorie restriction paradigm has provided one of the most widely used and most useful tools for investigating mechanisms of aging and longevity. By far, rodent models have been employed most often in these endeavors. Over decades of investigation, claims have been made that the paradigm produces the most robust demonstration that aging is malleable. In the current review of the rodent literature, we present arguments that question the robustness of the paradigm to increase lifespan and healthspan. Specifically, there are several questions to consider as follows:

  1. At what age does CR no longer produce benefits?
  2. Does CR attenuate cognitive decline?

  3. Are there negative effects of CR, including effects on bone health, wound healing, and response to infection?

  4. How important is schedule of feeding?

  5. How long does CR need to be imposed to be effective?
  6. How do genotype and gender influence CR?
  7. What role does dietary composition play?

Consideration of these questions produce many caveats that should guide future investigations to move the field forward.

To compare these findings in animals with how humans will react to fasting while infected, a general overview of fasting across different species might be useful and is documented here:
Marshall D. McCue: "Comparative Physiology of Fasting, Starvation, and Food Limitation", Springer: Heidelberg, New York, 2012.

  • I might be wrong as I'm not practising medical but I read various blogs and use websites like SE to keep myself educated about health and fitness. In general I like reading it. I read somewhere that when body starts burning fats and ketones starts circulating then the person develops bad breath (eg. Frooty odour in case of Ketones). Is there a correlation? Can you please explain in brief or should I post a completely new question using this answer as reference?
    – Heisenberg
    Commented Jun 1, 2020 at 19:42
  • @Heisenberg If it's really just a bit 'fruity' from ketones, and solely about that (metabolic or other problems might cause that, so be prudent): that's actually not that bad, imo, except many might mistake it for alc consumption. A bit of acetone and others are what the body produces and exhales. If it gets from 'funny' to 'stink' the diet is probably 'too extreme' medicalnewstoday.com/articles/325256#does-keto-work webmd.com/oral-health/features/… Commented Jun 1, 2020 at 20:40

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