Gut health comes down to the balance of the bacteria, archaea and eukarya that live in your gastrointestinal (GI) tract, also referred to as “gut microbiota1″.
Having a healty gut is crucial both for your physical and mental well-being.
Indeed, the gut microbiota not only contributes to a well-functioning digestion, but it also plays a significant role in the control of your immune system2, 3 and brain4, 5.
What is a healthy gut microbiota?
The definition of a “healthy” gut microbiota is yet to be defined.
This is due to the significant microbiota variance among apparently healthy persons, which has made it clear that “no single microbiome configuration is needed for health” (Shanahan et al., 2021, p. 485).
Rather, diverse compositions of the microbiome can be considered as healthy.
Since different bacteria often share the capability to conduct similar metabolic functions, the functional diversity of the gut microbiota is reduced5.
Therefore, researchers suggest that a functional definition of the microbiome might be superior to distinguish a normal from an abnormal microbiome.
Based on this type of definition, we can describe a healthy gut as one that effectively carries out its funcions.
Let’s explore them together.
5 Functions of the Gut Microbiota
One the most prominent roles of the gut flora is the performance of 5 metabolic functions that are vital to our survival:
- The metabolism of charbohydrates
- The metabolism of proteins
- The synthesis of proteins
- The synthesis of vitamins
- The mteabolic transformation of bile acids
1. Metabolism of carbohydrates
One of the main roles of the gut microbiota is the metabolisation of carbohydrates and, more specifically, of complex or “resistant” carbohydrates.
These consist in the portion of ingested carbohydrates that cannot be degraded by human digestive enzymes and, therefore, escape the digestion in the upper part of the gastrointestinal tract, where most of the carbohydrates are metabolized and absorbed as simple sugars7.
Hence, resistant carbohydrates – which include cellulose, hemicelluloses, inulins and resistant starch – reach the lower GI tract, and become available for microbial conversion (or “fermentation”).
Through the fermentation of undigested carbohydrates, the microbiota creates metabolites that can be used as energy sources.
This way, it contributes to a more efficient extraction from resistant carbohydrates.
Furthermore, microbial fermentation of carbohydrates generate – in addition to gases such as hydrogen and CO2 – short chain fatty acids (SCFAs), which have anti-inflammatory properties.
Here are the most important microbes that perform the degradation of complex carbohydrates:
- Bacteroides sp. or Ruminococcus sp., which metabolize cellulose and hemicelluloses in the human digestive tract. Thanks to them, 50-70% of the cellulose and hemicelluloses that we eat are digested after passing through the GI tract7.
- Bifiobacterium and others, which degrade inulin. In the fermentation process, these bateria break down the molecule to butyrate and other SCFAs that contribute to diverse health benefits8.
- Ruminococcus bromii, which metabolize resistant starch. In the process, they create acetate that Eubacterium rectale and Roseburia then transform into butyrate7.
2. Metabolism of proteins
Proteins are another important part of the human diet and they are mostly broken down by human digestive enzymes.
However, a portion of proteins – such as proteins of plant origin (which is less digestible than those of animal origin), and host-derived proteins contained in pancreatic juice, mucus and shed epithelial cells – are degraded through microbial fermentation in the colon.
As during the microbial fermentation of carbohydrates, the gut microbiota’s metabolization of proteins generates beneficial SCFAs.
However, it also generates toxic compounds such as “ammonia, amines, N-nitroso compounds, phenolic compounds and sulphides” (Rajilić-Stojanović, 2013, p.10).
Although the fermentation of amino-acids is performed by microbes belonging to different phylogenetic groups, research shows that bacteria belonging to the Clostridium cluster I and Atopobium seem to be the primary drivers of protein metabolism7.
3. Synthesis of proteins
The gut microbiota not only contributes to the metabolism of proteins, but also to their synthesis.
In fact, the gut microbiota has the capacity to create (essential) amino-acids that can be used by our body.
Therefore, the microbial synthesis of protein is especially important for individuals who eat a protein-deficient diet.
Research shows that dominant genera of the microbiota, such as Bacteroides, Roseburia and Streptococcus, are the main bacteria performing the synthesis of proteins7.
4. Synthesis of vitamins
Vitamins are extremely important for our health because they typically consist in “precursors of various enzymes that are necessary for vital biochemical reactions in all living cells” (LeBlanc, 2013, p. 160).
Since humans are not capable of synthesizing most vitamins, the gut microbiota’s role as a vitamin supplier is crucial for our well-being.
Research shows that the gut flora contributes to the synthesis of diverse vitamins, “such as vitamin K, and B group vitamins including biotin, cobalamin, folates, nicotinic acid, panthotenic acid, pyridoxine, riboflavin, and thiamine” (LeBlanc, 2013, p.160).
5. Metabolic transformations of bile acids
Finally, the gut microbiota plays an important role in the metabolic transformation of bile acids.
Bile acids are produced in the liver, and their secretion is linked to the ingestion of lipids, another important part of the human diet.
About 80% of bile acids that the liver releases in the intestine is absorbed in the terminal ileum into blood, and re-secreted in the process of enterohepatic recirculation7.
Intestinal bacteria such as the Bacteroides sp. metabolize the remaining 20% of the acids in the terminal ileum or colon.
How to Improve Gut Health Naturally
After defining what a healthy microbiome is and exploring the main functions it performs, let’s have a look at 3 research-based ways to improve gut health naturally:
- Reduce sugar consumption
- Eat many non-digestible carbohydrates
- Eat in harmony with your circadian rhythms
Let’s dive into them.
1. Reduce sugar consumption
The first way to improve gut health naturally is to reduce your sugar consumption.
A high-sugar diet increases the quantity of monosaccharides that are not absorbed in the small intestine, fostering the growth of microbes that can swiftly use these molecules (e.g., Proteobacteria) at the expense of other bacteria that are able to degrade complex carbohydrates (e.g., Bacteroidetes), which typically have slower growth rates.
The gut microbiota resulting from a high-glucose or -frutose diet – which is characterized by a reduced bacterial diversity, an abundance in Proteobacteria, and a scarcity of Bacteroidetes – shares “common features with microbiota dysbiosis associated with metabolic disorders, inflammatory bowel diseases (IBD) and other human disorders” (Satokari, 2020, pp. 1-2).
Furthermore, it is more prone to inflamation and less capable to perform immune-regulatory functions and epithelial-integrity control9.
Here is a list of foods and drinks that are suprisingly high in sugar (and you should stay away from!):
- BBQ sauce
- Salad dressings
- Pasta sauces
- Ketchup
- Fruit juice
- Granola
- Breakfast cereals
- Chocolate milk
- Flavored coffee
- Iced tea
2. Eat many non-digestible carbohydrates
Another powerful way to improve gut health naturally is to consume a diet rich in non-digestible carbohydrates (NDCs).
These consist in fibers – such as cellulose, hemicellulose, resistant starch and inulin – that the gut can ferment into short chain fatty acids (SCFAs).
The consumption of non-digestible carbohydrates fosters the synthesis of beneficial SCFAs and butyrate and it helps to increase stool frequency and better IBS and IBD symptoms7.
Furthermore, studies have shown that adding inulin – a resistant carbohydrate – to your diet fosters the growth of beneficial Bifidobacterium sp. and Faealibacterium pransnitzii related species, which are both reduced in people affected by IBS.
Low levels of Faecalibacteriums are also a marker of Crohn’s disease7.
Here is a list of foods that are rich in non-digestible carbohydrates that you incorporate in your diet:
- Leek
- Asparagus
- Chicory
- Rolled oats
- Leek
- Asparagus
- Chicory
- Rolled oats
- Bran
- Ginger
- Cabbage
- Navy beans
- Sweet potatoes
- White beans
- Turnip
- White beans
- Adzuki beans
- Lentils
- Nuts
3. Eat in Harmony with your Circadian Rhythms
Last but not least, you can improve your gut health naturally by eating according to your circadian clock.
The circadian clock is “the natural cycle of physical, mental, and behavior changes that the body goes through in a 24-hour cycle” (National Cancer Institute, 2022), and it manages and sustains proper rhythms in endocrine and metabolic pathways that are necessary for organism homeostasis10.
In fact, many physiological and metabolic changes – such as sleep-wake cycles, feeding behavior, body temperature, and hormonal levels – depend on the time of the day10.
Environmental changes, particularly daily light-dark cycles and rhythmic food intake, can lead to detrimental changes to the clock.
Like other systmes in our body, the microbiota composition undergoes diurnal oscillations and follows a specific circadian rhythm.
The disruption of rhythmic feeding times – for example thorugh time-shift-induced jet lag – is linked to dysbiosis, which results in a microbiota contributing to metabolic imbalances11 as well as increased risks of cariovascular diseases12.
To align your gut microbiota activity to your circardian rhythm – and, therefore, improve its functionality – you can practice time restricted eating (TRE).
TRE is a form of circardian fasting in which you restrict the time period in which you eat food, so that your gut microbiota has a specific feeding phase and a fasting phase.
This way of eating not only helps you achieving a healthy homeostasis in your gut, it also promotes the growth of good bacteria.
In fact, a 2-month TRE study showed that reducing the range of food intake time to 8-10h increases the abundance of beneficial microflora like Firmicutes, Clostridia, Ruminococcaceae, and Lactobacillus, while it decerases the harmful flora13.
Here are 3 steps to practice TRE and eat in harmony with your circadian rhythms:
- Reduce your eating window to 8-10h
- Keep your eating window consistent
- Eat your meals during daylight hours
Conclusion
I hope that you enjoyed this blogpost and that it will help you improve your gut health naturally ✨
If you have any comments, feedbacks or wishes, please let me know in the box below!
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References
- Thursby E, Juge N. Introduction to the human gut microbiota. Biochem Journal. 2017 May 16;474(11):1823-1836.
- Yoo, J.Y.; Groer, M.; Dutra, S.V.O.; Sarkar, A.; McSkimming, D.I. Gut Microbiota and Immune System Interactions. Microorganisms, 2020, 8, 1587.
- Moltanban-Arques et al. Selective manipulation of the gut microbiota improves immune status in vertebrates, Frontiers in Immunology, 2015, pp. 1-14.
- Bravo et al. Ingestion of Lactobacillus strain regulates emotional behavior and central GABA receptor expression in a mouse via the vagus nerve, 2011, Volume 108, Issue 38, pp. 16050 – 16055.
- Shanahan, F., Ghosh, T., S., O’Toole, P., W. The Healthy Microbiome—What Is the Definition of a Healthy Gut Microbiome?, Gastroenterology, Volume 160, Issue 2, 2021, pp. 483-494.
- LeBlanc, J. G., et al. Bacteria as vitamin suppliers to their host: a gut microbiota perspective, Current Opinion in Biotechnology, Volume 24, Issue 2, 2013, pp. 160-168.
- Mirjana Rajilić-Stojanović, Function of the microbiota, Best Practice & Research Clinical Gastroenterology, Volume 27, Issue 1, 2013, pp. 5-16.
- Brehm, C. U., Pfefferle, P. I.Inulin, the gut microbiome and the deeper breath of asthma patients – Novel pathways in asthma treatment, EBioMedicine, V. 46, pp. 15-16.
- Satokari, Reetta. 2020. High Intake of Sugar and the Balance between Pro- and Anti-Inflammatory Gut Bacteria, Nutrients, 12(5), pp. 1-4.
- Asher & Sassone-Corsi. Time for Food: The Intimate Interplay between Nutrition, Metabolism, and the Circadian Clock, Cell, Volume 161, Issue 1, 2015, pp. 84-92.
- Thaiss et al. Transkingdom Control of Microbiota Diurnal Oscillations Promotes Metabolic Homeostasis, Cell, Volume 159, Issue 3, 2014, pp. 514-529.
- Paoli A, Tinsley G, Bianco A, Moro T. The Influence of Meal Frequency and Timing on Health in Humans: The Role of Fasting, Nutrients, 2019 Mar 28;11(4):719.
- Yan, Yang, and Zhang. Maintain host health with time-restricted eating and phytochemicals: A review based on gut microbiome and circadian rhythm, Trends in Food Science & Technology, Volume 108, 2021, pp. 258-268.