Diet, gut and inflammation: in sickness and in health

Aim

The aim of this comprehensive review was to investigate the connection between inflammation, gut microbiota, and nutrition.

It further provided insight into how changes in eating habits may impact the composition and activity of the gut microbiota, which in turn influences inflammatory processes.

Finally, this review aims to aid in the development of practical approaches for the management and prevention of chronic inflammatory diseases.

Gut microbiome overview

The complexity of the gut microbiota is immense. The gastrointestinal tract is home to a variety of microbial communities, but the colon has the largest population, consisting primarily of bacteria, viruses, and parasites.

There are about 100 trillion bacteria in the human gut, weighing approximately 2kg and comprising up to 5000 different species. This is ten times more than the total number of microbial cells in the human body.

Humans are first inoculated with microbiota at birth, and these populations rapidly diversify in response to delivery method (vaginal vs. caesarean section), food (breastmilk vs. formula) and antibiotic use.

The microbiota plays a significant role in the development of the immune system, providing defence against pathogenic microorganisms and bacterial overgrowth. 

The microbiota continues to influence various processes into adulthood, such as the regulation of bone density, the modification and elimination of toxins, and the enhancement of intestinal barrier function.

Throughout life microbiota composition and function are influenced by a multitude of factors, such as host genetics, physiology, physical activity, stress, sleep patterns, medications, age, diet, and environmental exposures.

Nutrition is one of the factors that most influences bacterial composition. The microbiota is quick to adapt, often changing within 24 hours of dietary changes. 

Eubiosis, also known as “healthy microbiota”, is the state in which the microbiota in the intestines is in balance and has positive effects on the entire body.

Dysbiosis, or an imbalance in the gut microbiota, can disrupt these regulatory pathways, leading to chronic inflammation and contributing to various inflammatory diseases, including inflammatory bowel disease (IBD), rheumatoid arthritis (RA), and metabolic syndrome.

Increased intestinal permeability is a characteristic of dysfunctional gut barrier, often known as "leaky gut" (Figure 2), which permits infections, toxins, and antigens to translocate into the bloodstream.

Figure 1: Healthy gut vs Leaky Gut

The causes of dysbiosis are multifactorial and can be influenced by genetic, environmental, dietary, and lifestyle factors.

Autoimmune diseases, neurological disorders, obesity, metabolic disease, and IBD, have been linked to dysbiosis in terms of both onset and severity.

The gastrointestinal tract and the central nervous system are connected by the intricate and bidirectional gut-brain axis, which is vital for preserving homeostasis, behaviour, and mental health.

This axis includes several routes by which the gut microbiota might affect mood and brain function, including immunological, hormonal, metabolic, and neuronal signalling.

The diet gut connection

Dietary patterns significantly influence microbiota, inflammation, the immune system, and health outcomes.

The review explored three dietary patterns that offered unique insights into how dietary choices can shape the gut microbiota and influence inflammatory processes, thereby affecting overall health; western diet (WD), Mediterranean diet (MD), and plant-based diet (PBD).

Western diet (WD) is composed of high intakes of processed foods, red meats, sugars, and unhealthy fats. This type of diet is often associated with dysbiosis including reduced beneficial bacteria and increase in pathogenic bacteria in the gut.

Due to its high content of saturated, total fats, and highly processed food, the WD negatively affect the diversity and richness of the gut microbiota and has been connected to the advancement of metabolic disorders such as obesity, Type 2 diabetic mellitus (T2DM), IBD, obesity, atherosclerosis, and non-alcoholic fatty liver disease.

Mediterranean Diet (MD) is rich in fruits, vegetables, whole grains, nuts, and olive oil, and promotes a diverse and beneficial gut microbiota composition, contributing to anti-inflammatory effects and improved metabolic health.

Following a MD is associated with a number of health benefits, including heightened synthesis of short-chain fatty acids (SCFAs) and anti-inflammatory properties that mitigate the risk of chronic inflammatory diseases and metabolic disorders.

Plant-based diets (PBD) including vegetarian and vegan diets, which emphasize plant-based foods, enhance gut health by increasing the abundance of fibre-fermenting bacteria and the production of anti-inflammatory metabolites.

Eating fibre, complex polysaccharides, and vegetable proteins which are staples of the PB diet are shown to increase the number of beneficial bacteria in the body.

Plant-based proteins like pulses and pea proteins could lead to a rise in the number of good bacteria like Lactobacillus Faecalibacterium, Clostridium, Eubacterium, and Roseburia and a drop in the number of harmful species such as Bacteroides fragilis and Clostridium perfringens.Figure 1 

Figure 2: Mediterranean diet and Western diet.

Beneficial gut bacteria, especially Bifidobacterium and Lactobacillus, were much more abundant in those who ate a diet high in whole grains, like oats and barley. SCFAs, which are essential for preserving gut health and lowering inflammation, are less abundant in those eat refined grains.

Diet plays an important role in shaping the composition and functionality of the gut microbiota, which influences the gut–brain axis.

Having the ability to penetrate the blood-brain barrier, SCFAs can influence brain function and produce neurotransmitters like serotonin, which are essential for mood regulation and have anti-inflammatory properties.

Stress, combined with diets high in fat and sugar disrupt the microbiota, promote inflammation, and can negatively influence mood and cognitive function.

The complex interactions among nutrition, gut microbiota, and the gut-brain axis emphasises the significance of maintaining a well-balanced diet and effectively managing stress to enhance gut health and psychological wellness. 

Conclusion

Eubiosis is supported by beneficial dietary elements like fibre, polyphenols, plant proteins and healthy fats, which enhance anti-inflammatory pathways and general health.

In contrast, dysbiosis and increased inflammation is caused by diets heavy in refined sugars, refined grains, processed foods and saturated fats, aiding the onset and the advancement of chronic diseases.

The complicated relationships between inflammation, the gut microbiota, and diet highlights how crucial dietary decisions are to preserving health and averting chronic illnesses.

Diets high in fibre like MD and PBD encourage the gut microbiota to produce SCFAs, which have anti-inflammatory properties.

On the other hand, diets heavy in fat and sugar, which are common in WD, can damage the gut barrier by increasing inflammation and changing the microbiota's makeup.

Innovations in the treatment of chronic inflammatory disorders and improvement of human health may result from an understanding of the interrelated triangle (Figure 3) formed by inflammation, the gut microbiota, and nutrition. 

Figure 3: The interconnected triangle: diet, gut microbiota, and inflammation
  
The authors suggest future research should continue to explore the mechanistic pathways of this triad, aiming to develop targeted interventions that harness the power of the gut microbiota for disease prevention and management.

Therapeutic strategies, including probiotics, prebiotics, personalised nutrition, and faecal microbiota transplantation, also hold promise in modulating the gut microbiota to reduce inflammation and improve health outcomes.

Save article as PDF

Save article as PDF