“Boost your immune system with this weird trick!” This and similar nonsense can be found everywhere. But is it even possible to boost your immune system? And if so, is it even desirable? What supplements do you need to take? Is there even any value in doing so? Does body composition alter immunity? A lot of questions and I tried my best to answer them all. Spoiler: working on diet quality is always king.
First a little course in physiology. Our immune system has an innate, unspecific response and an adaptive, specific response. It works a little bit like security on an airport: security uses unspecific systems like the metal detector to make sure potential threats are discerned. And then there are specific systems like profiles of criminals that help security look out for known evil-doers. So far so good.
Our immune system works pretty close to optimal if everything is right (from a nutrition point of view). If your diet is crap, there may be deficiencies that make your immune system worse. However, a healthy balanced diet usually takes care of this quite easily (more on this later).
Can a diet improve your immune system to a higher than normal level? Long story short: nope. And it is good that your diet doesn’t increase the alertness of your immune system! To stick to the example above, imagine a hyperactive airport security system, that constantly arrests harmless passengers. The same thing would happen in your body and we know that that’s no good: allergic responses to harmless things like dust or peanuts. Autoimmune diseases like diabetes type 1 where the immune system mistakes your pancreas for a “bad” cell are the consequence of a misguided immune system.
So “boosting” your immune system is nonsense. However there are indeed a few things that can influence our immunity.
does body composition impact immune function?
In relation to body composition, infection risk seems to follow a U-shaped curve, with “normal weight” being associated with lowest risk, whilst both obesity and underweight seem to increase infection risk in adults. This shouldn’t surprise you, as it is pretty logical that neither being too fat or too skinny is the comfort zone of our body, where all processes are running close to optimal.
The mechanism why obesity can be problematic is still under discussion, but the accumulation of fat seems to disrupt lymphoid tissue integrity, which in turn disrupts immune function. Remember that obesity itself likely isn’t the only culprit of immune function, but the lifestyle choices of obese people, which are more on the unhealthy side than normal (less activity and higher intake of low-quality foods).
Why underweight people tend to be more ill than usual is likely just a matter of deprivation of “building blocks” our body needs to maintain immune function. These people eat so little, that deficiencies in literally quite everything are a problem, not so much a low body fat percentage per se.
What about fasting and dieting?
For most of us, dieting isn’t supressing our immune system. Only if you are already very, very lean and you have to diet aggressively, low food intake and low micro- and macronutrient intake that goes hand-in-hand with it, become problematic. We are talking weightclass restricted professional athletes here. For everybody else, this isn’t applicable. In fact, it probably helps obese people to lose fat and come closer to a healthy weight to improve immune function (see above).
I don’t know why fasting is commonly said to improve the immune system. As long as it is part of a weight loss intervention, this may be true, but still being in an healthy body fat range is the driver of better health, not fasting. However, short term fasting (like 1-2 days) or time-restricted feedling protocols (like intermittend fasting) seem to be perfectly safe. Long-term fast probably aren’t the best idea for your immune system, especially when you are already ill. Not eating anything and therefore not providing the body with any of the building blocks it needs to combat an infection seems counter-intuitive.
Macronutrients
There isn’t strong evidence to suggest that a specific carbohydrate content of the diet is “better” for immune function. It is likely that you can have good immune function on a wide range of carbohydrate intakes, from very-low to very-high, once other dietary factors are met (food sources, micronutrients, energy). There are claims that carbs for athletes are important because they seem to be beneficial for recovery, but evidence for this to impact immunity is pretty poor.
Pretty much any functional unit in our bodies consists largely of protein, so it is of no surprise that protein malnutrition increases susceptibility for infections. True malnutrition is relatively uncommon except in developing countries, but a higher protein consumption offers a wide spectrum of benefits and is a good idea anyways. Eat your protein!
The only fat that is of interest for immunity are omega 3 fatty acids, which directly impact the function of many types of immune cells. Although there is little evidence that omega 3 supplementation improves immunity in healthy individuals, similar to protein, omega 3 offers a wide range of health benefits and is generally a good idea to supplement (unless you eat plenty of fatty fish).
Micronutrients, supplements and others
The supplement and health food industry is quick to sell you their products, promoting them as “immune boosting”. As already mentioned, as long as our immune system has all the necessary building blocks, it just works and additional building blocks won’t benefit it. To stick to the airport security example, as long as all your metal detectors are working and you scan everybody, buying more metal detectors just for the sake of having them, doesn’t improve security. Similar to this, getting your micros in via a healthy, balanced diet is usually more than enough to be save.
A quick word to vitamin C because it is still promoted as the immune booster. Vitamin C is incredibly easy to get. Pretty much any fruit or vegetable has you covered. Additionally it is used by the food industry as a natural conservant, so even “junky” foods often are rich in vitamin C. No need to supplement.
Vitamin D is also worth mentioning as many people are deficient in it and it is very important for immunity. Even people who generally eat a healthy diet have a hard time getting enough vitamin D as it is almost only found in fatty fish and many people don’t like eating fish (guys, eat more fish!). Sunlight exposure is also important and most of us get too little of it, making vitamin D necessary to supplement for almost everybody.
While constant zinc supplementation doesn’t seem to be beneficial, and can be harmful if overdosed, acute zinc supplementation within 24 hours of the onset of symptoms has been shown to reduce the time of recovery for certain infections, especially the common cold.
You can forget about pretty much any other supplement. Fruits, veggies, nuts, legumes, meat, fish and dairy take care of all the vitamins, trace elements, fiber, polyphenols, probiotics and what not. Master the basics.
Diet quality
The typical Western diet (characterised by a diet high in sugar, trans and saturated fats, but low in complex carbohydrates, fibre, micronutrients, and other bioactive molecules such as polyphenols and omega 3 fat) is a risk factor for both obesity and chronic inflammation, both of which have been discussed as factors potentially altering immune function (in a bad way).
Dietary patterns rich in vegetables, fruit, nuts, legumes, fish, and unsaturated fat sources (especially omega 3) tend to be associated with lower levels of inflammatory markers. Plant-based diets are likely beneficial for overall “gut health” due to their high-fibre content, provision of micronutrients and polyphenols. You don’t have to go full vegan to reap these advantages, every healthy diet is based on eating lots of plants.
Yes, investing in high diet quality is really that important, and now we have an interesting study which shows ound that a 5% decrease in fruit/vegetable consumption was associated with a 12% increase in influenza-related hospitalization rates. Eating little fruits and vegetables literally increases the risk of ending up in the hospital.
Conclusion
Forget juices, smoothies, teas, pre-/probiotics and all that. Just eat like an adult: prioritise whole foods like meat, fish, veggies, fruits, nuts, legumes and whole grains. Diet quality is really that important. It takes care of macros, micros, fibre, your microbiome and your polyphenol intake. Supplement with vitamin D if you don’t get enough sunlight. Take omega 3s if you don’t eat fatty fish on a regular basis (by the way, there are also vegan options from algae). Zinc might help once you feel a little ill. Get your body fat in a healthy range, as being under- or overweight are both not very conducive for immune function. Fasting while being sick probably isn’t the best idea. Exercise, wash your hands, sleep, relax and enjoy life.
Are you struggling with a boring diet or are you not enjoying your training anymore? Contact us and let us talk how we can reach your body composition or strength goals and let training and eating be fun again!
Beary Strong 