Immune boosters – healthy microbiome

It seems that the human microbiome has become a hot topic in recent years. Lots of research has come out that shows us how important the bacteria (and other microbes) that live on our skin, gastrointestinal tract, lining of the respiratory system etc, are for our health. The Human Microbiome Project found 3,500-35,000 species inhabiting our body and there are actually more microbes in the body than there are body cells (9). Both good and bad microbes exist in our bodies, but in a healthy person there exists an appropriate balance between the two (1-3). However it is not exactly known what constitutes as a healthy microbiome, and what’s more, every person has their own unique composition of different microorganisms (9).

Most of the microorganisms that inhabit our bodies live in the GI tract, the small and especially the large intestine, but every surface of the body has microbes living on it. Our microbiome begins to develop as soon as we are born, and is hugely affected by our mother’s microbiome. As food becomes introduced and there is more connection with the environment, the microbiome becomes more stable, more varied, and mostly affected by the foods we eat. (1-3)

Onions and garlic are rich in the prebiotics inulin and fructooligosaccharides

Having a healthy microbiome helps us by modulating our immune system, providing fuel for the cells in our GI tract, and producing some vitamins, like vitamin K and B12. They can also break down potentially toxic substances from foods. The breakdown products of dietary fiber that microbes produce (short chain fatty acids, or SCFAs) not only maintain an acidic environment in your gut to prevent the growth of pathogenic bacteria, but they also might be beneficial for some chronic illnesses, like GI related diseases. (1, 9)

So a robust microbiome can keep us healthy in many ways, also through benefitting our immunity. Might it help us against the novel coronavirus?

Well, it is very unclear. I found a couple of articles exploring the “Gut-Lung Connection”. It appears that changes in the GI microbial environment affect the lung microbiome, and vice versa. For example, studies have shown that dysbiosis (imbalance) in the gut after antibiotic treatment may increase the risk of influenza infection in mice (2). Also, mice that had influenza had changes in their gut microbiome, even though influenza was not causing an infection in their gut (3). How this works in humans is still quite unclear (2,3). One study saw that probiotics supplementation reduced the number of respiratory infections in youths living in a foster home (5). SCFAs can also help reduce asthma symptoms, and protect against allergic airway inflammation, further elucidating the impact of gut microbiome on the lungs, though not much research exists on whether a healthy microbiome can prevent respiratory tract illness (3).

On a side note, growing up, I had asthma of sorts. I couldn’t exercise without getting an asthma attack and had to use inhalers. This disappeared about 10 years later, and I’ve been wondering what did it. Around the time that I stopped needing inhalers, I had improved my diet drastically, and was eating a lot more fruit and vegetables than before. It would make sense that the SCFAs from fiber, produced by my gut microbiome, had a positive influence.

How to keep your gut microbes healthy?

Foods rich in prebiotics (1, 5):  
Specific foods: Bananas, artichokes, leeks,
onions, garlic, asparagus, Jerusalem artichokes,
dandelion greens, and seaweed
Food groups: fruits, vegetables, beans,
whole grains like wheat, oats, and barley

To maintain a healthy microbiome, there are a few strategies to know about. You may have heard about probiotics and prebiotics. Probiotics are beneficial bacteria in foods and supplements, and prebiotics are the food that the bacteria need in order to thrive.

Firstly, provide the microbes in your gut good food (prebiotics) so that you can make sure the bacteria you want growing in your gut are well fed. Practically, this means getting enough fiber in your diet. Fruit, vegetables, whole grains, and beans are great sources of fiber that the good bacteria love. This ensures that good bacteria can thrive, which keeps the bad bacteria and other microbes in check, while providing us with all the health benefits. (5)

Secondly, many studies have shown that taking probiotics have many health benefits, such as inhibiting the development of pathogenic bacteria, improving non-alcoholic fatty liver disease, increasing the body’s immunity, and improving IBS (irritable bowel syndrome) symptoms, among others. However, certified health claims credited to probiotic products are not currently in place due to insufficient data (9). Fermented foods, like sauerkraut, kimchi, yogurt, kombucha and other probiotic drinks, are laden with different kinds of probiotics, but probiotics are also sold in pill form (5, 9). However, how well these can stick around in your gut is questionable. One article I found stated that most of the bacteria we eat pass right through, and a consistent supply of these to the gut is needed for sustained effects. (6). Furthermore, a recent review article of many studies concluded that probiotics can lead to improvement in the gut microbiota of healthy individuals, but only in a transient manner. (7) Different strains of the same bacteria may also have different effects in the gut (9).

The prebiotic in banana is inulin

I read through a lot of papers written on this huge – and growing – field. There is much that science doesn’t know yet about the microbiome, or about probiotics, but it is evident that having a robust microbiome is crucial for our health. Based on what I read, eating lots of foods that can feed the good bacteria is the most important thing we can do, since everyone has their own individual composition of microbes that probiotic supplements might not be able to parallel, and since microbes taken by mouth seem to not have lasting effects anyway. Many foods that contain probiotics have other beneficial aspects to them, so if you are looking to take probiotics, eating foods like yogurt or sauerkraut, might be the way to go. Also, since no health claims are approved for probiotics, they belong to the supplement category and are thus not required to have an FDA approval.

So, eat your fruit and veggies.

Thank you for reading! Until next time,


Do you take probiotics, or prebiotics? Let me know in the comments how they have helped you.

Photos by Manol Manolov (


  1. The microbiome.
  2. Anand and Mande. Diet, Microbiota and Gut-Lung Connection. 2018!po=5.68182
  3. Marsland et al. The Gut–Lung Axis in Respiratory Disease. 2015.
  4. Bingula et al. Desired Turbulence? Gut-Lung Axis, Immunity, and Lung Cancer. 2017.
  5. Markowiak, Slizewska. Effects of Probiotics, Prebiotics, and Synbiotics on Human Health. 2017.
  6. Bezkorovainy. Probiotics: determinants of survival and growth in the gut. 2001.
  7. Khalesi et al. A review of probiotic supplementation in healthy adults: helpful or hype? 2018.
  8. Reid et al. Probiotics: Reiterating What They Are and What They Are Not. 2019.
  9. Day et al. Probiotics: current landscape and future horizons. 2019.

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