By Healing Diets Coach Graduate, Kylie Williams HDC

The gut microbiota is a complex ecosystem of its own, which has a heavy influence on overall health. This article looks at the effects of phytochemicals on gut health, based on a summary of scientific studies collated in 2022.

The gut microbiota has a role in:

• Digestion
• Absorption
• Overall health

Phytochemicals & Gut Microbiome

Plants secrete phytochemicals which accumulate in the cell wall and cell sap compartments of the plant to aid the plant’s development and survival. Phytochemicals are non-nutrient biologically active plant components that can modify the composition of gut microflora through selective stimulation of proliferation or inhibition of certain microbial communities in the intestine.

They are received into the body and recognised as xenobiotics. They are poorly absorbed in the small intestine; rather, they enter the large intestine and reside there as their absorption is low. Then they are metabolised by gut bacteria. Their action on gut bacteria is being studied and is a relatively new area of research with some contradicting results; however, many studies conclude and agree on the following:

• Phytochemicals can alter the composition of microbial ecology beneficially by acting as prebiotics.
• Phytochemicals often have antimicrobial actions in the gut against harmful gut microbiota.
• Phytochemicals influence bacterial quorum sensing, allowing increases in the abundance of healthy bacteria.
• This may also interfere with signalling pathways involved in the process of disease development.
• Phytochemicals may have inhibitory action on unhealthy bacteria such as Helicobacter pylori.
• Example: The action of polyphenols, including green tea and red wine, has shown to suppress production of toxin VacA (Vacuolating toxin A), which is a primary virulence factor of Helicobacter pylori. This results in the destruction of bacterial cell membranes, suppression of urease activity, and disturbance of bacterial multiplication.

The Kingdom of Gut Bacteria

The kingdom of gut bacteria resides in each and every one of us and is one of the most densely populated and diversified bacterial ecosystems in nature. Known as our gut microbiome, it consists mainly of anaerobic bacteria, but also fungi, protozoa, and viruses. It resides in the large intestine and is involved in the fermentation of undigested food particles, including fats, carbohydrates, and proteins.

In a healthy state, this contributes to overall health and wellbeing; however, in an unhealthy state, it has the opposite effect. Around 400 BC, Hippocrates is said to have quoted, “Death sits in the bowels”.

• There are around 100 trillion bacteria, and approximately 1,000 different species have been identified.
• The surface area of the human GI tract is between 260–300 m2.
• This complex system used to be considered as simply an excretion system in medical science; however, it is now considered an essential organ of health.

The types and numbers of microbes vary along the GI tract. In the first portion of the small intestine (the duodenum), the pH is similar to that of the stomach, and the population of gut microbes is significantly less than further along into the large intestine, where pH increases (5.7–6.8). There should be a more concentrated, complex, and diverse microflora community here. This is also affected by the composition and physiology of both the lumen and mucus layer of the intestinal tract.

From birth until approximately age 3, we have an important role to play in influencing a healthy microbiome. At age 3, the phylogenetic diversity of microflora is established, and a stable and complex microbial ecosystem is generated.

Firmicutes and Human Health

Firmicutes play a significant role in the relationship between gut bacteria and human health. They break down carbohydrates in the gut that cannot be digested by the body’s enzymes (e.g., dietary fibre and resistant starch) by fermentation. This produces metabolites including vitamins and short-chain fatty acids like butyrate. Butyrate helps to prevent inflammation and fuels the lining of the gut to maintain a healthy colon.

Butyrate:

• Is a source of energy for the cells of the gut lining.
• Stimulates glutathione production.
• Helps prevent cancer by preventing cancer cells from developing.
• Encourages hormone production for healthy metabolism.

Studies have shown a relationship between the ratio of Firmicutes to Bacteroidetes and body weight/obesity. Obesity is associated with higher amounts of Firmicutes and lower Bacteroidetes; however, there are limited studies to support this. We do know that flavones help to improve this relationship. There are also studies which correlate lower levels of butyrate with people experiencing IBS symptoms.

Prebiotics (fibres and starches that the body cannot easily digest) are a source of energy for Firmicutes; these include fruits, vegetables, legumes, and whole grains. Supporting these will help to increase butyrate. Conversely, foods that have a negative effect on the health of the gut microbiota include those high in animal protein, fat, and sugar.

Gut Health and Metabolic Disease

Colonic microflora shows an interaction with metabolic diseases. The intestinal ecosystem contributes heavily to optimum human health by contributing non-human genome encoded enzymes, including the generation of vitamins and the breakdown of phytochemicals to form metabolites that contribute to health.

The intestinal microflora may be responsible for metabolic disorders including obesity, hypertension, cardiovascular disease, diabetes, and inflammation. They play significant roles in human physiology including:

• Regulation of colonic function.
• Immune system modification.
• Toxin removal from the body.
• Defense against several pathogens.
• Energy homeostasis, which is interrelated with insulin resistance and obesity.
• Altering the signalling pathways associated with the initiation and progression of inflammation.

Some studies have found that chronic low-grade inflammation is generated by the interaction between a person’s diet and their intestinal microbiome. There is a reciprocal association between the diet and gut microbiome. Phytochemicals in food form part of this picture, as do vitamins, minerals, dietary fibre, fats, eating a toxin/additive-free diet, and lifestyle factors such as exercise and a balanced stress response.

Dysbiosis

In an unbalanced or unhealthy state, the gut microbiota plays a negative role in health and may be one of the factors contributing to dysbiosis, alongside diet, insufficient exercise, stress, age, drugs, and metabolic factors. Dysbiosis and disease are closely related. In the GI tract, dysbiosis can lead to:

• IBD
• Crohn’s Disease
• Ulcerative Colitis
• Colorectal cancer

It may also lead to disorders associated with “extra metabolism” such as diabetes, obesity, and cardiovascular disease. It should be noted that the term “dysbiosis” has no official definition as yet. We use the term to refer to an altered state of health in the digestive system where factors like intestinal permeability, gastrointestinal motility, visceral hypersensitivity, and the gastrointestinal immune system may be affected.

Paying attention to gut health through diet, exercise, and beneficial changes to pH can help the favourable bacteria (symbionts) to thrive while removing pathogenic bacteria (pathobionts). This contributes strongly to whole-body health.

Gut Health and Phytochemicals

Phytochemicals have the ability to “selectively” encourage the growth of some bacterial populations in the gut known as probiotics, which include yeast, Bifidobacterium, lactic acid bacteria, and Bacilli involved in metabolism. They also inhibit gut dysbiosis by enhancing the prevalence of beneficial bacteria species and enhancing diversity. They reduce the abundance of opportunistic harmful bacteria, which supports intestinal barrier function. This results in decreased metabolic diseases and their related complications.

Phytochemicals are just part of the picture; gut health is influenced by many more aspects of diet and lifestyle, including minerals, vitamins, essential fatty acids, pH, stress, and hydration. All phytonutrients have antioxidant and anti-inflammatory benefits.

Specific Research on Phytochemical Groups

1. Polyphenols

Polyphenols are categorised into flavonoids (flavones, flavanones, flavanols, flavonols, flavanonols, isoflavones) and non-flavonoids (phenolic acids, stilbenes, curcumin, tannins, lignans, coumarin). They have low bioavailability; their benefits occur via metabolites from interactions with gut microbiota.

• Flavonoids: More than 6,000 have been identified, notably containing pigments that give colour to flowers. They act as free radical scavengers.
• Flavones: Found in parsley, red peppers, celery, chamomile, peppermint, and coriander. They lower the ratio between Firmicutes and Bacteroidetes, which has been shown to help weight loss.
• Flavanols: Found in white, green, and black tea, apples, grapes, blueberries, and strawberries. They are in higher concentrations in fruit skin. Diets high in flavanols may act as prebiotics. Catechin (high in green tea and berries) has strong anti-cancer action, improves intestinal permeability, and promotes beneficial bacteria.
• Flavonols: Found in onions, kale, grapes, red wine, tea, and broccoli. Quercetin and kaempferol are most studied. Quercetin is found in elderberry, oregano, and dark chocolate. Kaempferol is found in capers, cumin, and cloves. These significantly improve Lactobacillus, Bacteroides, and Bifidobacterium while suppressing bacteria related to obesity.
• Flavanones: Found in citrus fruits, mint, and tomatoes. They suppress harmful microbes and activate beneficial ones. Hesperidin (citrus) increases Lactobacillus. Citrus extract has shown to increase the ratio between butyrate and short-chain fatty acids.
• Isoflavones: Found in soy and legumes. Studies on post-menopausal women showed a significant increase in Bifidobacteria after administration.
• Anthocyanins: Responsible for red, purple, and blue colours. Gut microbiota convert them to metabolites in the large intestine, which increase favourable bacteria like Lactobacillus and Bifidobacterium. They help healthy bacteria compete for adhesion sites and are effective against H. pylori. They also improve oral health by preventing collagen breakdown.

2. Stilbenes

• Resveratrol: Sources include muscadine grape red wine, cranberries, strawberries, and peanuts. It is anti-diabetic and anti-obesity. It reduces body fat by altering colonic microflora and promotes Lactobacillus and Bifidobacterium.
• Piceatannol: Sources include black grapes and red wine. It significantly alters gut bacteria to favour beneficial strains.

3. Lignans

Phytoestrogens found in flax seeds and grains¹²². Estrogen-like activity occurs once metabolised, producing enterolactone and enterodiol¹²³. They improve antioxidant status, prevent cancer by limiting cell proliferation, and improve immunity¹²⁴.

4. Tannins

Widely distributed in nature. Pomegranate tannins accelerate the total number of gut bacteria and increase the prevalence of Lactobacteria and Bifidobacteria. Condensed tannins (proanthocyanidins) also cause shifts in gut bacteria.

5. Curcumin

Extracted from turmeric rhizome, it re-establishes gut microbiota (especially in estrogen deficiency) and increases butyrate-generating bacteria. It stimulates anti-inflammatory markers and inhibits inflammatory mediators in the intestine.

6. Phenolic Acids

Split into Hydroxybenzoic and Hydroxycinnamic acids. Sources include bran, berries, olive oil, and wholegrains.

• Caffeic Acid: Found in dried sage, spearmint, cinnamon, and coffee. It enhances Akkermansia (beneficial for obesity/diabetes) and suppresses the Firmicutes/Bacteroidetes ratio.
• Protocatechuic Acid: Found in star anise, chicory, and olives. It lowers inflammatory microbes like Helicobacter and increases beneficial Firmicutes and Actinobacteria.
• Ellagitannins: Found in pomegranates, walnuts, and berries. Campylobacter jejuni and Candida albicans are susceptible to cell wall degradation by these compounds.

7. Organosulfur Compounds

Garlic is the richest source. Ingestion of whole garlic increases the diversity of the gut microbiome.

8. Carotenoids

Responsible for red, orange, and yellow colours. They include carotenes (lycopene) and xanthophylls (lutein). They are fermented in the colon and act as antioxidants.

• Astaxanthin: Found in shrimp, salmon, and microalgae. It reduces H. pylori and liver inflammation.
• Lutein: Remarkably increases the abundance of Lactobacilli and Bifidobacterium.
• Lycopene: Found in watermelon and tomatoes; it promotes Bifidobacterium longum.

Additional Factors

Exercise improves the tight junctions of the epithelial tissue in the digestive tract. Note: The phytochemical properties of many herbs increase significantly when the herb is dried.

References

• Santhiravel, S., et al. (2022). The Impact of Plant Phytochemicals on the Gut Microbiota of Humans for a Balanced Life.
• Ben Brown (June 2023). Nutritional Gastroenterology: Matching New Treatments to New Disease Subtypes.
• Phenol-Explorer Database.