BLOG BY Dr Jenna Macciochi, PhD FHEA

Feed A Virus And Starve A Bacteria

Yes, the season of colds and flu is now in full swing. Headache, fever, aches & pains: colds and flu can be miserable! These familiar miserable symptoms of seasonal lurgy’s are not caused by the germs themselves but part of our immune systems reaction to it in its quest to fight the infections.  Even after a cold or flu has run its course, it takes some time for things to return to normal. In this sense, you might only feel fully better only when your immunity stops fighting, which may be some time after the unwanted germy houseguests have already been eliminated, leaving some symptoms caused by inflammation to linger even longer.

While there is no cure for the viruses that cause these seasonal lurgy’s, that doesn’t mean you’re helpless against it.  In the annual scramble for cold and flu remedies, you've probably come across the old adage “feed a cold and starve a fever.” But is that sound advice? 

Sickness behaviours

The presence of a fever is usually related to stimulation of the body's immune response to infection. Fever can support the immune system's attempt to gain an advantage over infectious germs. Your immunity can respond to invading germs faster. Also, higher body temperatures make it harder for germs to thrive in the body  (1, 2). When us humans come down with a fever, we often lose our appetites and shun food. Lack of appetite and fever are infection-induced behavioral changes, collectively known as “sickness behaviors.” These behaviors are considered to be evolutionarily developed to protect us from infections.

Exploring whether presence or lack of nutrition might influence recovery from infections have revealed some fascinating insights. It looks like there really may be a scientific truth behind this old wives tale. But if we really want to be accurate, the statement should be: “feed a virus, starve bacteria.”

Why does eating affect bacterial and viral infections differently?

Even though we can lose appetite, keeping our nutrition up is actually important for our recovery (3). Hence feed a cold (which are caused by viruses).  Carbohydrates, rather than fat or protein, are the critical macronutrient our immunity needs to fuel an immune response to viruses. So what about starve a fever? The evidence shapes up to be dramatically different.  When it comes to bacterial infections, we also can lose appetite, often for quite some time. In contrast to viral infections, fasting can be protective from fever caused by bacteria. This is because the type of immune response caused by bacteria is so destructive to our own cells and tissues that fasting limits the availability of fuel for the immune response, limiting it from going over the top and causing collateral damage. Specifically carbs seem to be the most important macronutrient to withhold as these are the preferred fuel for our immunity foot soldiers as they do their job. 

Mice are not humans

So, what to do if you or a loved one comes down with a cold, the flu, or another viral bug this season? It’s too early to say as much of this was studied in mice, not humans. And mice are not humans so the findings need to be replicated and confirmed in people. But, in the meantime, it appears that when you have a typical viral syndrome such as a cold or flu, a carb rich meal or snack probably wouldn’t hurt—and might even help. Just be sure first that it’s not a serious bacterial infection. So maybe this is what Grandma meant when she told you to “starve a fever, stuff a cold.” Science aside, aim to eat to hunger and not worry too much as you probably won’t know if your infection is viral or bacterial unless your doctor does some investigative tests. 

Why your appetite may matter when seriously ill

While most of us will survive a cold or flu regardless, what these studies highlight is that there are key differences in how immune responses are fueled for different types of infection.  To eat, or not, might be more important to improve survival of critically ill patients in intensive care units where what you feel like eating when you don’t feel well may be your body’s way of telling you how best to optimize your response to that infection. Studies looking at patients with Sepsis (a serious bacterial infection of blood) and shown improved survival when food is withheld. Critically ill patients often cannot feed themselves, so doctors generally feed them during the time of critical illness. If we could understand the role of appetite in infection, we could provide more rational care for infected patients at home and in the hospital.

This post was written by, Dr Jenna Macciochi who is based in Brighton, she is an immunologist and lecturer at the university of Sussex. Her work has a specific focus on the role of diet and lifestyle in inflammation and immunity. Jenna is also a qualified fitness instructor and mother to 5 year old twins. You can find her on Instagram @dr_jenna_macciochi


C. V. Harper, D. J. Woodcock, C. Lam, M. Garcia-Albornoz,  View ORCID ProfileA. Adamson, L. Ashall, W. Rowe, P. Downton, L. Schmidt, S. West, D. G. Spiller, D. A. Rand, and  View ORCID ProfileM. R. H. White. Temperature regulates NF-κB dynamics and function through timing of A20 transcription. PNAS May 29, 2018 115 (22) E5243-E5249

Thomas A. Mace  Lingwen Zhong Casey Kilpatrick  Evan Zynda Chen‐Ting Lee Maegan Capitano  Hans Minderman Elizabeth A. Repasky. Differentiation of CD8+ T cells into effector cells is enhanced by physiological range hyperthermia. Journal of Leukocyte Biology.  Volume90, Issue5. November 2011. Pages 951-962

Wang A, Huen SC, Luan HH, Yu S, Zhang C, Gallezot JD, Booth CJ, Medzhitov R. Opposing effects of fasting metabolism on tissue tolerance in bacterial and viral inflammation. Cell.2016 Sep 8;166:1-14.

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