Immunity and gut microbes
What we eat has a significant impact on the gut microbiota, and on our immune system.
The influence of gut microbes on many aspects of human physiology is significant (1). From supporting the body’s nutritional, metabolic, immune and nervous system functions to the production of important metabolites, essential vitamins, hormones and neurotransmitters, the impact of the human gut microbiota on health is huge.
It is now widely understood that a healthy interaction between the gut microbiota and our immune system is essential for the maintenance of our body’s homeostasis and health. A diverse and healthy gut microbiota from early life is crucial for this, as it teaches the immune system that not everything is bad. This is evident because disruption of the gut microbiota affects the body’s immune response, which in turn can lead to the development of disease (2).
A healthy interaction between our immune system and the gut microbiota is crucial for the maintenance of health.
The gut microbiota co-develops with its human host and communicates closely with the body’s immune system from birth. Through this communication the microbiota and the immune system shape each other and work together in a mutualistic relationship, known as symbiosis (3). We are only beginning to understand the extent of this mutual relationship. However, they appear to work together via a a network of interactions to help provide resistance against invaders, respond to infection and inflammation, and promote tolerance to harmless microbes - thus preventing autoimmune dysfunction (4).
Our immune system co-evolved with the gut microbiota from birth. They work together to keep us healthy and protect us against unwanted microbes.
For infants, the important early life microbes Lactobacilli and Bifidobacterium are the first teachers that instruct the developing immune system about what is dangerous and what is not, as well as providing protection (4). The developing gut microbiota helps support the development of immune cells as well as train and fine tune the immune system. In return, the immune system promotes the growth of beneficial microbes and helps maintain a stable gut ecosystem. Together they set the stage for the development of the more adult-like microbiota, which occurs by around 3 years of age.
As infants develop and grow they begin to eat a more complex diet, acquiring more microbes from their family, food, infections and environmental surroundings. Whilst we do not yet know what the perfect gut microbiota looks like, we do know there is much we can to look after it. There are many factors that influence the gut microbiota throughout life including age, environment, stress, illness, toxins and medication for example. However, diet is a major player.
Diet plays a major role in shaping the composition and activity of gut microbes, as well as influencing many aspects of the microbiota-immune interaction.
Given the key role diet plays in the composition and activity of gut microbes, it should come as no surprise that what we eat has a significant impact on the gut microbiota, and consequently our immune system (5). Gut microbes get most of their nutrients from our diet and produce physiologically important compounds (some of which have already been mentioned) such as short chain fatty acids. Short chain fatty acids (SCFA) are produced when gut friendly bacteria in the colon ferment the indigestible part of plant material. These SCFA’s contribute to our daily energy, facilitate nutrient availability, promote gut health and importantly aid immune function and resistance to illness and disease (6).
In contrast, a gut microbiota that is ‘starved’ of gut-friendly food provides an environment for potentially harmful microbes to thrive in the absence of a healthy gut ecosystem. Harmful microbes can produce toxic compounds that may compromise gut health and trigger an immune response which may result in inflammation, autoimmune dysfunction and the development of disease (1).
It is important to look after our gut, and this starts with what we eat.
The modern ‘Western’ diet, characterised by excessive intake of highly processed, energy-dense food, animal protein, saturated fat and simple sugars, along with a low intake of dietary fibre is increasingly linked to an imbalanced (dysbiotic) gut microbiota with low microbial diversity and high levels of harmful microbes. Thankfully, dietary changes can shift the composition of the gut microbiota. Consuming a diet that is rich in a diverse range of plant foods that can be converted into beneficial metabolites, including SCFA, helps keep the gut microbiota and immune system healthy.
Gut microbiome testing provides detailed insight into the microorganisms inhabiting the gut and how they function.
Gut microbiome testing provides information about your unique gut microbiome composition and how it affects your health. Digest Health provides comprehensive gut microbiome testing by Microba, and personalised dietary advice about how to achieve a better balance between beneficial and less beneficial microbes in your gut that support healthy immune function and better overall health.
References
CA. Thaiss, N. Zmora, M. Levy, E. Elinav. The microbiome and innate immunity. Nature (2016) pp. 65-74.
S. Mezouar, Y. Chantran, J. Michel, A. Fabre, J-C. Dubus, M. Leone et al. Human Microbiome Journal 10 (Dec 2018) pp. 11-20
JK. Nicholson, E. Holmes, J. Kinross, R. Burcelin, G. Gibson, W. Jia, S. Pettersson. Host-gut microbiota metabolic interactions. Science (2012) pp. 1262-7.
Y. Belkaid, T. Hand. Role of the microbiota in immunity and inflammation. Cell (2014) pp.121-141.
MA. Conlon, AR Bird. The impact of diet and lifestyle on microbiota and human health. Nutrients (2014) pp. 17-44
JR. Marchesi, DH. Adams, F. Fava, et al. The gut microbiota and host health: a new clinical frontier. Gut (2016) 65:330-339.
