Health: a nutritional perspective on immune health

Health. The dictionary defines it as ‘the state of being free from illness or injury’. I think many would go further and define it not just as the absence of some sort of trauma, but the presence of a certain level of physical, mental and social ‘wellbeing’. 

Regardless of the definition you go for, maintaining an appropriately functioning immune system is clearly a key component of health. It is key to fighting disease when necessary and repairing injury. It also has a role in adapting to training. 

Adequate sleep, limited psychological stress, moderate levels of physical activity and nutrition all play a role in maintaining the immune system. And it is worth recognizing that all these elements are interlinked. Nothing in the body stands alone! For example, there is increasing evidence that diet impacts sleep and sleep impacts diet. This article will focus on what we understand from studying nutrition and immune health specifically. But it is worth noting that nutrition can also directly influence other factors that can further impact immune function. 

So, the basics …

Can’t fight something with nothing

The immune system needs to be built from something and run on something. If we are very low on energy or lacking a macronutrient (in particular protein, we think) there appears to be an increased risk of infection. So extended periods of cutting weight, particularly if you are already lean, may leave you more susceptible to falling ill with an infection. It may also lead to higher injury risk if your soft tissue and bone are not able to repair and maintain itself.

Get your micros!!

A functioning immune system depends on vitamins and minerals!! Zinc, vitamin C, vitamin D to name but a few. Eat a diverse range of foods that are minimally processed to help ensure you get the full spectrum of vitamins and minerals to support health. Eat all the colors of fruit and veg, aiming for at least 4-5 handfuls total a day. Get a variety of other foods … nuts, seeds, whole grains, meat, fish, dairy, plant-based proteins. If there are food groups you don’t eat, for medical, ethical, taste or religious reasons find out if you are at higher risk of a micronutrient deficiency and find alternative foods these are in (or supplement under medical supervision if necessary). 

It is worth noting that although we can obtain limited amounts of vitamin D from foods we make most of our vitamin D in our skin in response to sunlight. As a result, some degree of vitamin D deficiency is thought to exist in most northern hemisphere populations, particularly in winter, due to lack of sunlight. As such, the UK government recommends healthy adults supplement with 10ug of vitamin D daily between October and March.

And maybe your microbes …

This is an interesting one, and we are definitely still figuring it out! The gut lining has an immune system, and it turns out this has a role not just in keeping the gut free from infection, but also supporting the immune system of the whole body. And we think that the gut bacteria have a role in supporting the functioning of the gut immune system. So – at least in theory – if we maintain a diverse and functioning gut bacteria population we may support the whole body immune system. And how do we support such a bacterial population?

• Fibre and resistant starches!! aka ‘Microbe accessible carbohydrates’. We can’t digest these, but they are vital foods for the ‘good’ bacteria in our guts. These are found in fruits, vegetables, whole grains, pulses, and beans. Eat a range for the full variety of foods our different bacteria need. 

• Include polyphenols. These are small molecules found in certain foods that seem to help increase the good bacteria in the gut and limit the bad bacteria. Rich sources of polyphenols are good quality olive oil, spices such as cumin and cinnamon, nuts, seeds, and dark berries. 

• Limit refined sugars. In other words, the stuff added to biscuits, cakes, candy, ice cream and other processed foods (including savory ready meals!). These appear to be the favorite food of many species of ‘bad’ bacteria. Limit these to help limit the amount of these bacteria.  

• Probiotics. Certain foods contain bacteria. These foods are called probiotics. Live yogurt, kefir, kimchi, sauerkraut, unpasteurized cheese, sourdough, miso, and other fermented foods. Except wine and beer … the alcohol content and pasteurization of these kills the bacteria (sorry!). Eating these might help top up or support the ‘good’ bacteria in the gut, even if they don’t reach the gut alive. You can also buy probiotic supplements, but I would take care here if you don’t have a particular illness (more on this below!). Most supplements contain a lot of limited types of bacteria, and even if these are ‘good’ you may not want to risk them taking over in the gut. We usually want to keep a full range in there! So I would recommend only using these under the guidance of a qualified medical practitioner. 

And is there anything special about athletes?

We know that a moderate amount of physical activity boosts the immune system. By moderate we mean a few times a week, 30 to 60 minutes a session, getting the heart rate up, sweating, moving around, and maybe lifting some weights. 

We used to think that athletes, i.e. those undertaking repeated high-intensity lungs burning up dead on the floor conditioning sessions, or repeated days of multiple hours of exercise back to back had some level of immune depression and were less able to fight infection. So they got sick more, especially with upper respiratory tract and, in some sports, gastro infections. 

As we learn more it seems that athletes may not have a lowered ability to fight infection (resistance), but may have a disrupted immune tolerance. Immune tolerance is the ability to launch an appropriately sized immune response. This means ignoring things when the body deems them not to be a threat (like the bacteria in our guts) and cutting ‘threatening’ bacteria and other infectious things to a tolerable level if we deem we don’t need to entirely clear them out. If our tolerance is too high we end up with our insides being damaged by nasty infections our body should be responding to. If our tolerance is too low we get sick easily as our body tries to fight off everything even when it is not a big threat.

We think the cause of this lowered tolerance in athletes could be a combination of the stress of the physical activity itself, the psychological stress of training and competition, lack of sleep when traveling, exposure to novel pathogens in different training and competition sites and hotels, and inappropriate nutrition.

What does lowered immune tolerance mean practically, in terms of nutrition? Aside from doing what we can with the basics to support our immune system (i.e. those points above) the following may further support immune tolerance or reduce the risk or burden of infection in athletes: 

• Avoiding dehydration during training and generally, as saliva has antimicrobial properties and is, therefore, the first line of defense in bacteria entering the mouth.

• Ensuring adequate carbohydrate availability during exercise bouts that are, in particular, over 60 minutes (see here: ). Although there is some debate as to whether this is actually relevant, and so views may change in the coming years. 

• Taking 75mg a day of zinc acetate at the onset of a head cold

• Taking certain probiotics may help reduce the number of episodes of upper respiratory tract infection and travelers diarrhea in athletes. But it is dose and strain dependent, so consult a professional before giving it a go!

• Taking up to 1g of vitamin C may help reduce the incidence of upper respiratory tract infections in people undertaking repeated strenuous bouts of exercise, and 3-4g a day may help reduce the duration of an upper respiratory tract infection. However, intake should be considered against the potential impact on training adaptations (read here: https://www.feedfuelperform.com/post/antioxidants-can-you-have-too-much-of-a-good-thing).

So there you have it. There is no magic bullet. Getting the basics right can go a long way. And infection may be a time when supplements are called for, in some individuals. And importantly … there is still a lot we don’t know!! So watch out in the coming years as we research and learn more.

Read more

• www.mysportscience.com article by Michael Gleeson: ‘What can you do to reduce become infected with respiratory pathogens?’

• Neil Walsh’s 2019 review published in Sports Medicine (Volume 49, Supplemental Section 2, page S153): ‘Nutrition and Athlete Immune Health: New Perspectives on an Old Paradigm’

• The 2015 publication in the Cochrane Database of Systematic Reviews: ‘Probiotics for preventing upper respiratory tract infections’

• The 2020 review from researchers in the School of Medicine at the University of Madrid published in Nutrients (Volume 12, Issue 2, page 579): ‘Role of Vitamin D in Athletes and Their Performance: Current Concepts and New Trends’

Dr. Sinead Robers - FeedFuelPerform