This article is about the connection between gut health and the health of the whole body. It highlights the role of gut microbiota on nutrition and the impact of gut health on the body as a whole which ranges from the mood to the immune system. It highlights how the food we eat directly impacts the health of our gut microbiota and consequently the health of our whole body. It further explores the foods that can improve the function of our gut and hence our health. In our understanding of how gut health affects our overall health, it is important to acknowledge the significant role of gut microbiota in health. One of the essential tasks of our gut microbiota is to assist in the absorption of nutrients from the food we consume. When our gut is unhealthy or when the quality of our gut microbiota is low, the effect is reflected in the poor health of the whole body. It is evident that microbiota is a major factor in the quality of our nutrition and thus in our health.
Understanding the Gut Microbiota
Definition and role of gut microbiota
The gut microbiota, often referred to as gut flora or gut bacteria, is the community of microorganisms living in the gastrointestinal tract and includes bacteria, viruses, fungi and other microbes. Gut microbiota influences health and wellbeing.
The gut microbiota plays a crucial role in digestion and absorption of nutrients, regulation of the immune system, synthesis of some vitamins, and protection against pathogens. Because of its many important functions in different physiological processes, the gut microbiota is often referred to as ‘the forgotten organ’.
Components of a healthy gut microbiota
A healthy gut microbiota is marked by high microbial diversity, with a great variety of different beneficial bacteria, including Bacteroidetes and other groups of Firmicutes, and a small proportion of potentially harmful bacteria, all living in harmony.
But the gut microbiota also includes viruses, fungi and other microbes, which collectively affect the wellbeing of the host (you) with its gut microbiome by interacting with each other and with bacteria.
How microbiota establishes in the gut
The development of the gut microbiota begins at birth. The neonatal gut is sterile at first, but it rapidly becomes colonised by microorganisms from the maternal birth canal and breast milk. The early colonisation of the gut is determined by a wide range of factors, including the mode of delivery (vaginal versus caesarean), breastfeeding, and use of antibiotics.
Due to diet, stress, medications and illness, the composition of gut microbiota can shift throughout one’s lifetime, but maintaining a diverse, balanced gut microbiota with a healthy lifestyle and proper care is possible.
The Relationship Between Gut Microbiota and Nutrient Absorption
How gut microbiota affects the processing and utilisation of nutrients
The gut microbiota is involved in the digestion and absorption of food nutrients. It helps us break down complex carbohydrates, proteins and fats that our body is not able to digest by itself. Bacteria in our gut secrete enzymes that can degrade these big nutrient molecules into smaller nutrient molecules that are then absorbed into the body.
In addition, the gut microbiota produces SCFAs as a byproduct of dietary fibre fermentation. SCFA are absorbed through the colon, providing energy for colonocytes and helping to regulate gut function.
Interaction of gut bacteria with different types of macronutrients
Certain types of macronutrients prompt distinct responses from the gut microbiota. For instance, dietary fibre (the edible portion of plants that humans and some other animals are unable to digest) – abundant in fruits, vegetables, whole grains and legumes – is a prebiotic, which is defined as a nondigestible food ingredient that promotes the growth of beneficial microorganisms in the gut.
High-protein diets enrich and increase the abundance of some bacterial species that specialise in protein breakdown, which can lead to increased and unbalanced production of potentially harmful byproducts, namely ammonia and sulphides, both of which are connected to inflammation and gut dysbiosis.
Implications of gut bacterial diversity on nutrient absorption
We will have a healthy body only if we have a gut microbiota that is diverse. If the gut microbiota is diverse, it will provide the various enzymes that help in digesting and absorbing the nutrients which are present in the diet through various pathways. If the gut microbiota is not diverse, then the enzymes needed to break down and absorb nutrients will not be available, leading to poor nutrient digestion and absorption.
Moreover, decreased microbial diversity in the gut has been linked to obesity, diabetes and inflammatory bowel disease, while increased diversity is associated with improved metabolic health and reduced risk of chronic disease.
Gut Microbiota and Metabolic Functions
Role of gut microbiota in digestion and metabolism
Through its influence on food digestion, the gut microbiota plays a key role in the intestinal absorption and whole-body metabolism of diverse nutrients. It is particularly important in the digestion of complex carbohydrates, proteins and fats that humans cannot digest by themselves, as the bacteria in our digestive system produce digestive enzymes that break down these nutrients in a way that can make them more accessible and usable.
Furthermore, fermentation of dietary fibre by the gut microbiota produces various metabolites, including short-chain fatty acids (SCFAs) such as butyrate, acetate and propionate. These SCFAs supply energy for colonocytes and help to regulate intestinal functions.
Contribution of gut microbiota to the energy balance
The gut microbiota can affect energy regulation; there is evidence that it influences the harvesting and use of energy from food. Very efficient bacteria succeed in extracting more energy from food, hence more calories become absorbed.
Furthermore, the gut microbiota can impact storage and utilisation of fat by the body. Disruptions in microbiome composition, including overgrowth of some types of bacteria, have been linked to increased fat storage and obesity.
Gut microbiota and the regulation of body weight
Researchers have suggested that body weight is regulated, at least in part, by the gut microbiota, since people with a greater variety of gut bacteria also tend to have a healthier body weight than those with low bacterial diversity.
Furthermore, some species of bacteria, including Akkermansia muciniphila, are linked to a lean phenotype and improved metabolic health via regulation of energy balance, inflammation and barrier function in the gut.
A healthy body weight and absence of metabolic disorders can be promoted by preserving a healthy gut microbiota by a proper diet and lifestyle.
Implications of Gut Microbiota on Immune System
Influence of gut microbiota on immune response
The gut microbiota is critically important for establishing and regulating the immune system, teaching and training immune cells to recognise harmless compounds from potentially dangerous pathogens. This occurs through a number of different pathways, some of which involve production of immune signalling molecules and interaction of gut bacteria with immune cells.
This immune tolerance is believed to be partly due to a healthy gut microbiota, which dampens excessive or unnecessary immune responses to innocuous substances like some food antigens, and also partly from the production of anti-inflammatory cytokines.
Gut microbiota’s role in inflammation and autoimmune diseases
Alterations or dysregulation in the composition of the gut microbiota can result in dysregulation of the immune system, leading to a state of chronic inflammation. Chronic inflammation in the gut has been implicated in a variety of autoimmune conditions, including inflammatory bowel disease (IBD), rheumatoid arthritis, and type 1 diabetes.
The health of your gut microbiota may also affect how you respond to inflammation throughout your body, since research shows that a balanced microbiota modulates the immune system to optimise your body’s pro- and anti-inflammatory responses to keep diseases at bay.
Bacteria as a line of defence against pathogens
The gut microbiota serves as a protective barrier by competing with pathogens for nutrients and adhesion sites in the gut. Bacteria in the gut also synthesise antimicrobial substances that prevent pathogens from growing and establishing a foothold in the gut.
Furthermore, the gut microbiota enhances the barrier function of the gut, thus preventing bacteria or toxins from the gut to enter the bloodstream. This barrier function is very important for maintaining a healthy gut and protecting against infections.
So a healthy gut microbiota is important for a strong immune system and for protecting us from pathogens.
Gut Microbiota and Mental Health
The gut-brain axis and its implications
Signals to and from the gut – a two-way street – are carried by many different kinds of molecules, via the gut-brain axis. Neural, hormonal and immune signals are transmitted from the gut to the brain in significant numbers.
Gut-brain communication is integral to mood, behaviour and mental health – and the gut microbiota is the messenger. It is the microbes in your gut that manufacture neurotransmitters and metabolites capable of altering brain function and behaviour.
Impact of gut microbiota on mood and behaviour
The available evidence suggests a correlation between mood disorders (psychiatric disorders such as depression and anxiety) and the gut microbiota. Compositional alterations in the gut microbiota have been found in people suffering from mood disorders.
Moreover, results from animal studies indicate that modifying the microbiota through probiotics or faecal microbiota transplantation (FMT) can lead to profound alterations in behaviour and mood. This means that the microbiota could become a therapeutic target for mental health disorders.
Gut microbiota’s association with mental health disorders
In fact, there is mounting evidence that dysbiosis of the gut microbiota is linked to conditions such as ASD, ADHD and schizophrenia. Several studies are now looking at whether modulation of the gut microbiota can help to ameliorate symptoms and improve outcomes in these conditions. However, it will take more research to understand how to harness the gut-brain axis to improve mental health.
Association of Gut Microbiota with Chronic Diseases
Gut microbiota’s role in cardiovascular diseases
Recent studies suggest that gut microbiota might contribute to the development of cardiovascular diseases including atherosclerosis and hypertension. Unfavourable changes in the proportions of gut microbiota, especially an overgrowth of certain bacteria, lead to an increase in inflammation and metabolites produced by microorganisms that contribute to these diseases.
In addition, the gut microbiota regulates lipid metabolism and cholesterol absorption, both of which are central in cardiovascular health. Indeed, a healthy gut microbiota is a key regulator of cardiovascular diseases.
Contribution of gut microbiota to obesity and diabetes
The gut microbiota has been implicated in the development of obesity and type 2 diabetes; people with obesity have a different profile of gut microbiota than those who are lean.
Certain species of bacteria, including Firmicutes and Bacteroidetes, have been linked with obesity and metabolic dysfunction, and they regulate energy extraction from the diet, fat metabolism and systemic inflammation.
Moreover, gut microbiota dysbiosis has been shown to be associated with insulin resistance – a hallmark of T2D. The dysbiotic gut microbiota can lead to glucose intolerance, insulin resistance and T2D.
The impact on cancer
Emerging evidence indicates that gut microbiota dysbiosis, characterised by an altered abundance of beneficial and harmful bacteria, might be implicated in the development and progression of cancer, particularly colorectal cancer. Nevertheless, individuals with colorectal cancer often have a reduced abundance of beneficial bacteria and an increased abundance of potentially pathogenic bacteria.
The gut microbiota can affect multiple pathways that drive the cancer process, including inflammation, damage to DNA, and carcinogen metabolism, so a healthy gut microbiota achieved through appropriate diet and lifestyle can minimise the risk of some cancers.
The Effect of Antibiotics on Gut Microbiota
Impact of antibiotic usage on gut bacteria
Antibiotics are among the most effective drugs to treat infections caused by bacteria. But they can have unintended effects on the gut microbiota. Antibiotics can kill or inhibit the growth of bacteria, whether these are pathogenic or helpful.
Antibiotics are effective at killing harmful bacteria, but can also change the balance of the microbiota – they can reduce the overall bacterial diversity, lead to overgrowth of antibiotic-resistant bacteria, and promote the growth of potentially pathogenic bacteria.
Long term effects of antibiotics on gut microbiota
It remains unclear how antibiotics affect the gut microbiota in the longer term, but there is evidence suggesting that antibiotic use can lead to lasting changes in the composition of the gut microbiota after antibiotic treatment has ended.
In fact, changes in the diversity and composition of gut microbiota can be observed for months, or even years, following antibiotic use. Long-term alterations in gut microbiota are known to be linked to an increased risk for infections and development of chronic diseases.
Rebuilding gut microbiota after antibiotic treatment
When you finish a course of antibiotics, here are some strategies you can try to restore a healthy gut biome:
Probiotic supplementation: Probiotics are live beneficial bacteria that can help to replenish the gut microbiota. Probiotics can be present in some foods such as yogurt and fermented vegetables, or they can be taken as dietary supplements.
Eating prebiotic foods: Prebiotics are indigestible fibres that feed healthy bacteria. Foods to eat include onions, garlic, bananas and whole grains. Eating prebiotic foods feeds healthy bacteria in the gut.
Eat a diverse and healthy diet: A diverse and healthy diet provides a broad range of nutrients, prebiotics and fibre which serve as food for a healthy microbiota. A diet with varied fruits, vegetables, whole grains and fermented foods could help you maintain a diverse microbiota.
Age-Related Changes in Gut Microbiota
Shifts in gut microbiota across lifespan
Their composition changes markedly over the course of our lifetime. The gut microbiota tends to differ between infants and young children to adults. It evolves during childhood and adolescence, and becomes relatively stable over the course of adulthood.
However, as we age, the microbiota continues to change, with a loss of bacterial diversity and shifts in the relative abundance of different bacterial species. In particular, this age-related decline in gut microbiota diversity has been linked with poorer health in older adults.
Changes in gut microbiota during ageing
As people age, their dietary habits, activity levels, medication use and gut motility can change, all contributing factors to changes in gut microbiota composition.
Another factor that seems to affect the gut microbiota is a decline in immune function, which is also seen as people get older. Since immune function slows down, there’s less of the beneficial bacteria and more of the potentially harmful bacteria in the gut.
Impact of these changes on health and disease
Changes in composition of the gut microbiota that occur with age can set the stage for health or disease at older ages. Low gut microbiota diversity has been linked to frailty, cognitive decline and susceptibility to infections.
Furthermore, changes in the microbiota can alter the metabolism of drugs, resulting in altered drug efficacy and side effects in older adults. Maintaining a healthy gut microbiota by adopting healthy lifestyle choices such as eating properly and exercising regularly can help to preserve a healthy stage of the gut microbiota and promote healthy ageing.
Diet and Gut Microbiota
Influence of dietary habits on gut microbiota
For example, different dietary components such as fibre, fats, sugars each have distinct effects on the composition and diversity of the gut microbiota, which in turn affects different functions.
A high-fibre diet, mostly from fruits, vegetables, whole grains and legumes, favours the growth of beneficial bacteria in the gut, which ferment dietary fibre and produce short-chain fatty acids (SCFAs) – compounds that provide many health benefits.
On the other hand, diets high in processed foods, added sugars, and unhealthy fats can lead to the overgrowth of potentially harmful bacteria in the gut, which can lead to obesity, metabolic syndrome and inflammation by causing imbalances in the gut microbiota.
Role of prebiotics, probiotics, and fermented foods
Prebiotics and probiotics are nutritional supplements that can favourably affect the microbiota of the gut.
Prebiotics are non-digestible fibres that feed beneficial bacteria in the gut. They act like food for these microbes, helping them to flourish and maintain a healthy gut microbiome. Prebiotics can be found in foods such as onions, garlic, bananas, asparagus and whole grains.
Probiotics, in contrast, are live bacteria or yeasts that confer health benefits when consumed in sufficient numbers, either in certain foods (such as yogurt, kefir, sauerkraut and kimchi) or in supplements.
Fermented foods that contain beneficial bacteria – such as yoghurt, kefir, sauerkraut and miso – can be a good addition to a diet that is striving to increase gut microbiota diversity.
How a diverse diet can benefit gut microbiota
A varied diet will encourage a varied gut microbiota, because this means that your gut microbiota is exposed to a range of nutrients and compounds that can support different species of bacteria.
Adding a range of fruits, vegetables, whole grains, legumes, nuts and seeds to the diet is essential to support the gut microbiota with a diverse range of nutrients and dietary fibres. A diverse diet also promotes gut microbial diversity, which in turn is associated with better health and a lower risk of chronic disease.
Maintaining a Healthy Gut Microbiota
Adopting a balanced diet for a healthy gut microbiota
One of the most important things you can do for your gut microbiota is eat a balanced diet. In other words, a diet that has a good variety of nutrient dense foods from all food groups.
Make sure that you consume a diversity of fruits, vegetables, whole grains, legumes, nuts, seeds, lean proteins and healthy fats, all of which are rich in nutrients and fibres that help keep your gut microbes happy.
Furthermore, minimise intake of processed foods, added sugars, unhealthy fats and excessive alcohol – dietary factors that might harm the gut microbiota and foster imbalances that can lead to ill health.
Physical exercise and gut microbiota
Physical exercise may influence the gut microbiota for the better: regular exercise can lead to a more varied and well-balanced composition of the gut microbiota.
It’s recommended that doing 150 minutes a week of moderate-intensity aerobic exercise, such as purposeful walking, jogging or cycling, is a sufficient amount for good general health. This level of activity has been linked to favourable changes in the microbiota.
Similarly, strength training exercises (eg, weightlifting or resistance training) are also beneficial to the gut microbiota, and it is good to aim to do strength training two or more days a week to reap the full health benefits.
Potential benefits of microbiota transplantation
Microbiota transplantation, otherwise known as faecal microbiota transplantation (FMT), involves transferring faecal material from a healthy donor into the gastrointestinal tract of a recipient, usually to treat recurrent Clostridioides difficile infection. FMT is also being studied in other conditions.
FMT has proven to be a promising therapy for restoring a healthy gut microbiota and improving symptoms for certain conditions, including inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS).
However, it should still be emphasised that FMT remains an investigational procedure, to be done solely within the purview of a healthcare professional, and in a controlled clinical setting.
Conclusion
To wrap it up, we need to pay attention to the role of gut microbiota to maintain the normal physiological functions for human health. The gut microbiota is involved in the process of nutrient utilisation and metabolic activities, immune regulation and mental health, as well as the prevention of chronic disease. A balanced diet, regular exercise, and the potential interventions of probiotics and prebiotics should be taken to maintain the health of gut microbiota.
