Healthy microbiota has a positive effect on the absorption and metabolism not only of carbohydrates and fibre in our daily diet, but also of minerals, vitamins, food supplements and, last but not least, drugs.
Zinc, for example, is an essential trace element for multiple cellular functions. More than 300 enzymes and thousands of transcription factors contain one or more zinc atoms, and even a slight zinc deficiency can lead to major immune imbalance and interfere with thyroid function. The gut microbiota influences zinc bioavailability, utilisation, and metabolism. When microbiota is rich in friendly species, it should hoard zinc supplies by 'stealing' it from bacteria that would use it to maintain the good functioning of the transport systems necessary for their colonisation and virulence. These include bacteria such as Campylobacter jejuni, Escherichia coli, Salmonella spp, Proteus mirabilis, Haemophilus influenzae, and so on.
Selenium is a trace element necessary for thyroid function. The concentration of selenium in the thyroid gland can remain stable for a long time irrespective of dietary intake. Studies show that selenium is also essential for the functioning of certain enzymes with antioxidant action called seleno-proteins, such as glutathione peroxidase, iodothyronine deiodinase and thioredoxin reductase. The gut microbiota influences the availability, absorption, storage, and utilisation of selenium by our cells through its influence on selenoproteome expression. Several species of bacteria possess endogenous selenoproteins which they use to grow. These bacterial proteins therefore utilise selenium for their own purposes, thus reducing its availability to the thyroid. Conversely, the presence of bacteria capable of stimulating anti-inflammatory cytokines such as IL-10 increases the expression of the protein that transports selenium to the thyroid, thereby increasing its bioavailability. Similarly, an adequate dietary intake of selenium improves the gut microbiota and stimulates microbial diversity.
Iron supplementation is a frequently adopted clinical strategy to treat martial deficiency. However, it has been observed that alterations in microbial diversity in the gut microbiota and a pro-inflammatory shift may occur after iron supplementation. In addition, the gut microbiota responds differently depending on the chemical form of dietary iron supplementation. Ethylenediaminetetraacetic acid (EDTA) for example, compared with iron formulations, has resulted in a reduction in Roseburia intestinalis, a beneficial bacterial strain of the colonic microbiota. Similarly, it has been observed that oral administration of iron, compared to intravenous administration, was associated with a lower occurrence of butyrate-producing bacterial strains such as Faecalibacterium prausnitzii. The administration of iron remains an essential strategy for maintaining good health. Nevertheless, to promote better absorption and reduce its negative effects on microbial composition, the presence of strong and healthy microbiota is of the utmost importance.
As well as micronutrients, there are many substances whose excess may have an impact on the intestinal microbiota. Food additives, present in almost all processed foods, contribute to significant alterations in microbial composition. Emulsifiers, present in food products to increase their consistency, reduce the protective mucus layer, altering mucosal permeability and contributing to an increase in bacteria that convert fighter bacteria to hydrogen sulphide, whose excessive presence can lead to an increase in inflammatory load. Similarly, artificial sweeteners severely alter the microbial balance, increasing clostridia, bacteroides, and total aerobic bacteria. Glyphosate, used in plant protection products, in addition to its direct toxicity, affects the intestinal microbiota, stimulates the presence of potentially harmful bacteria, such as Fusobacterium nucleatum, and reduces the presence of Lactobacillus spp and other butyrate-producing bacteria.
Finally, drugs also interact with the microbiota. The last few years have seen the emergence of a new line of research: 'pharmaco-microbiomics'. 'Pharmaco-microbiomics' aims to study the complex interactions between drugs and the microbiota. Scientific research is increasingly observing how drugs can affect the composition of the microbiota and how the intestinal microbiota can modulate the absorption, distribution, and action of the various active ingredients of pharmacological products. The most studied drug-microbiota interactions are certainly those involving antibiotics, paracetamol, proton pump inhibitors (PPIs), NSAIDs and metformin.