In the age of coronavirus, the most popular two words around the world are “social distancing”. While these are new words, to avoid predation from physical weakness and to prevent the experience of calorie-gulping sickness from acute infection, man has been practicing the concept of the “behavioral-immune system” for centuries in order to avoid full engagement of the expensive immune system.


We are in a worldwide lockdown due to the novel coronavirus pandemic that is defying economies, monarchs, powers, technology, and so far, except for supportive therapy, even modern medicine. Due to the pandemic and stay at home advice, the functions of the immune system have bubbled to the top of health-related discussions, including well-meaning advice on home exercise to “build”, “boost” or “strengthen” the body’s immunity. On its face, these words assume that the immune system is a well-defined organ like the skeletal muscle that can be bulked up in strength and size with different kinds of suggested exercises. However, like all systems, the immune system consists of billions of cells and proteins that work intricately to detect and destroy non-self invaders, such as parasites, viruses and bacteria. It is safe to say that immune cells in healthy individuals are several times more than the population of all the world’s soldiers put together.

In real life, despite our so-called multitasking, we still prioritise one or a few activities over several others because it’s practically impossible to do all we would like to do at one time. Same goes for the whole-body system, as all organs and systems of an average adult, of all races if I may add, require a range of 2,500 to 3,000 calories per day. The brain and immune system are both selfish and metabolically expensive, but unlike the brain and the heart whose calorie requirements are often non-negotiable, energy allocation to the immune system only takes high priority in the presence of infection.

In other words, the body cannot support all organs and physiological processes on pre-allocated limited energy income without running into energy conflicts. However, a sedentary lifestyle promotes an opportunistic chronic activation of the immune system in the absence of infection and may lead to heart disease, diabetes and some cancers. Therefore, in good health condition, the immune system is in an energetically conservative state but becomes metabolically expensive in the presence of infection.

In what an author describes as “live before philosophise” or “shock and awe” in military jargon, the immune system demands dramatic high energy in acute infections, forcing the body to obligatorily reallocate a significant amount of energy to it. This high demand is usually brief but must resolve within three days to six weeks before the body runs out of stored energy…


In another time, I would endeavour to explain how physical exercise assists in prioritising low energy allocation to the immune system in normal health and avoids energy conflict with its selfish cousin, the brain. However, the question is how expensive is the immune system in a state of acute infection? A good example I could find in literature is fever, which is caused by proteins called cytokines that are produced by activated immune cells. According to a review, an 80-kilogram man would require more than 250 calories per day to maintain a fever of 1 degree Celsius (about 2 Fahrenheit). In energy perspective, the same person requires 273 and 168 calories per day for his brain and heart respectively.

In what an author describes as “live before philosophise” or “shock and awe” in military jargon, the immune system demands dramatic high energy in acute infections, forcing the body to obligatorily reallocate a significant amount of energy to it. This high demand is usually brief but must resolve within three days to six weeks before the body runs out of stored energy, with the potential for death as outcome. In acute infection, physical activity is not a priority and is therefore put on “lockdown” to conserve already stored energy by inducing the sickness behaviour, which includes physical weakness and loss/lack of interest in pleasurable activities such as food, social interaction, sex, learning, etc.

In the age of coronavirus, the most popular two words around the world are “social distancing”. While these are new words, to avoid predation from physical weakness and to prevent the experience of calorie-gulping sickness from acute infection, man has been practicing the concept of the “behavioral-immune system” for centuries in order to avoid full engagement of the expensive immune system. This behaviour explains the feeling of disgust with the smelling or sighting of rotten food that may harbour harmfully bacteria and reluctance to try new food for fear of getting sick, including assigning new food as safe or dangerous after the first experience.

As we continue to stay indoor, we should try to look beyond the boredom of the lockdown and focus on the huge reward of staying alive. Again, lets “live and then philosophise”.


For safety and self-preservation in constantly changing environmental threats, man has not only been able to demonstrably avoid the claws and jaws of physical predators but has always been able to avoid the “invisible enemy”, to quote President Trump, even before the modern advanced knowledge of pathogens, and long before the discovery of antibiotics and preventive vaccines. The word “novel” precedes coronavirus because this is the first-time humans are exposed to this virus and are yet to acquire the adaptive immune system to fight the COVID-19 disease. According to the World Health Organisation, the protective measures against new infection includes cleaning hands regularly and thoroughly with alcohol-based hand rub or water and soap; maintain social distancing; and avoid touching the eyes, nose and mouth. Finally, it recommends that you stay at home if feeling unwell but call your physician early if you have fever, couch and difficulty in breathing.

As we continue to stay indoor, we should try to look beyond the boredom of the lockdown and focus on the huge reward of staying alive. Again, lets “live and then philosophise”.

Mukaila Kareem, a doctor of physiotherapy and physical activity advocate, writes from the USA and can be reached through makkareem5@gmail.com