In recent years, we have been hearing more and more about the importance of the gut microbiome for our health. In this article, we will explain what the gut microbiome is, how it affects our body, and its potential relationship with obesity. We will then present simple and practical ways to support and improve it.

What is the gut microbiome?

The gut microbiome refers to the collection of microorganisms (bacteria, fungi, and viruses) that inhabit the digestive system. The human gastrointestinal tract contains a diverse microbial community comprising more than 100 trillion microorganisms. The density of bacterial cells in the colon has been estimated at 10¹¹ to 10¹² per milliliter, making the colon one of the most densely populated microbial habitats. The gut microbiome encodes more than 3 million genes that produce thousands of metabolites, whereas the human genome consists of approximately 23,000 genes. The phyla Firmicutes and Bacteroidetes account for around 90% of the total microbial community, while other phyla such as Proteobacteria, Actinobacteria, and Verrucomicrobia are less dominant. Among the approximately 200 genera belonging to the Firmicutes phylum are Lactobacillus, Bacillus, Clostridium, Enterococcus, and Ruminococcus, while the predominant genera within the Bacteroidetes phylum are Bacteroides and Prevotella. The gut microbiome is influenced by age, diet, geographical factors, and antibiotic use.

What is the role of the gut microbiome?

The gut microbiome plays a vital role in nutrient metabolism. More specifically, it is responsible for the fermentation of carbohydrates in the large intestine, a process that produces short-chain fatty acids (SCFAs), which serve as an energy source for the human body. In addition, it participates in lipid metabolism and the synthesis of vitamin K and B vitamins. The gut microbiome also contributes to the breakdown of polyphenols, drug metabolism, the maintenance of gastrointestinal barrier integrity, and, of course, the homeostasis of the immune system.

How is the gut microbiome related to obesity?

It has been estimated that by 2030, 38% of the global population will be overweight and 20% will be living with obesity. Obesity is a chronic disease and is closely associated with the development of cardiovascular disease, type 2 diabetes, respiratory disorders, and liver disease. It results from a positive energy balance, influenced by both genetic and non-genetic factors, including individual, environmental, and dietary factors.

According to studies conducted in animals, the gut microbiome appears to be associated with the development of obesity. In 2021, researchers examined 32 studies and conducted a meta-analysis investigating the composition of the gut microbiome in individuals with and without obesity using DNA sequencing techniques. The meta-analysis reported the following findings:

1. Individuals with obesity tend to have lower bacterial diversity in the gut, which is associated with a less favorable metabolic profile.

2. Individuals with obesity tend to have a higher Firmicutes-to-Bacteroidetes ratio. This means that the gut microbiome of these individuals contains a greater abundance of Firmicutes, which may contribute to increased energy extraction from food and, consequently, greater fat storage. However, there was considerable heterogeneity among the studies.

3. Individuals with obesity have lower levels of Bifidobacterium. These bacteria contribute to digestion and help reduce inflammation, making them beneficial to health. Therefore, their reduced abundance in people with obesity is considered unfavourable.

However, the researchers highlighted the need for more standardised and larger-scale studies in order to draw more robust conclusions.

How can I improve my gut microbiome?

Diet plays a fundamental role in shaping the composition of the gut microbiome. The following steps can help improve your gut microbiome:

Increase your fiber intake: Dietary fiber supports the growth of beneficial microorganisms. In addition, fiber undergoes fermentation by gut bacteria in the large intestine, resulting in the production of short-chain fatty acids (SCFAs), which lower the pH of the colon and help prevent the growth of Gram-negative pathogenic microorganisms such as Salmonella and Escherichia coli.

Sources: Fruits (apples, berries, bananas, oranges, pears), vegetables (broccoli, cauliflower, onions, carrots), legumes, oats, barley, wholegrain products, wheat, rye, nuts, and seeds.

Consume probiotic-rich foods: Probiotics are live microorganisms that, when consumed in adequate amounts, provide health benefits, including preventing the growth of harmful bacteria in the gut, supporting immune function, and aiding lactose digestion. They mainly belong to the Lactobacillus and Bifidobacterium genera.

Sources: Fermented foods such as yoghurt, especially sheep's and goat's yoghurt, kefir, certain cheeses such as cottage cheese and mozzarella, fermented vegetables and pickles such as sauerkraut, kimchi, and pickled vegetables, soy products such as tempeh, and beverages such as kombucha (fermented black or green tea).

Avoid high-fat diets: Scientific evidence shows that diets high in fat, particularly saturated and trans fats, are associated with unfavourable changes in the gut microbiome, alterations in the faecal metabolic profile, and increased levels of pro-inflammatory markers in the bloodstream. In contrast, diets lower in fat promote the growth of beneficial bacteria, including the genera Blautia and Faecalibacterium.

Foods to avoid: Processed meats and cured meats, such as sausages and ham; foods deep-fried in high-temperature vegetable oils, such as fast-food French fries; ready-made baked goods such as doughnuts, croissants, and biscuits.

Limit ultra-processed foods and food additives: Food additives refer to artificial or natural substances added to foods to improve color, flavor, taste, or processing characteristics. These include emulsifiers, acidity regulators, leavening agents, colorings, bleaching agents, flavor enhancers, preservatives, sweeteners, thickeners, and many others. Many of these additives may disrupt the balance of the gut microbiome and promote inflammatory responses.

Foods to avoid: Foods containing emulsifiers, such as ice cream, sauces, dressings, and ready-made baked goods; foods containing artificial sweeteners, such as soft drinks and chewing gum; and foods containing preservatives, such as ready-to-drink juices, canned foods, packaged sweets, and savory snacks.

Increase your physical activity: Physical activity increases the diversity of the gut microbiome and improves the Bacteroidetes-to-Firmicutes ratio, which may contribute to weight loss. It also promotes the growth of bacterial species that can enhance mucosal immunity and help protect against gastrointestinal disorders and diseases, including colorectal cancer. Therefore, incorporating both aerobic and resistance exercise into your daily routine is highly recommended. Simple ways to achieve this include choosing brisk walking instead of driving and performing resistance training at home with exercise bands or strength training with weights at the gym.

If you would like personalized nutritional guidance to help restore your gut microbiome, improve your wellbeing, and achieve sustainable weight loss, contact us here.

References

• Pinart, M., Dötsch, A., Schlicht, K., Laudes, M., Bouwman, J., Forslund, S.K., Pischon, T. and Nimptsch, K. (2022) ‘Gut Microbiome Composition in Obese and Non-Obese Persons: A Systematic Review and Meta-Analysis’, Nutrients, 14(1), p. 12. Available at: https://doi.org/10.3390/nu14010012.

• Rinninella, E., Raoul, P., Cintoni, M., Franceschi, F., Miggiano, G.A.D., Gasbarrini, A. and Mele, M.C. (2019) ‘What is the Healthy Gut Microbiota Composition? A Changing Ecosystem across Age, Environment, Diet, and Diseases’, Microorganisms, 7(1), p. 14. Available at: https://doi.org/10.3390/microorganisms7010014.

• Su, Q. and Liu, Q. (2023) ‘Factors Affecting Gut Microbiome in Daily Diet’, Nutrients, 15(6), p. 1510. Available at: https://doi.org/10.3390/nu15061510.

• Jandhyala, S.M., Talukdar, R., Subramanyam, C., Vuyyuru, H., Sasikala, M. and Nageshwar Reddy, D. (2015) ‘Role of the normal gut microbiota’, World Journal of Gastroenterology, 21(29), pp. 8787–8803. Available at: https://doi.org/10.3748/wjg.v21.i29.8787.