Posted on 15 October 2023
An increasing amount of evidence suggests that the microorganisms living in our guts play an important role in ageing and disease. These microbes are collectively known as the gut microbiota. The exact composition of the microbiota changes from person to person, but also changes during ageing and in response to environmental factors like diet.
To study the gut microbiota, scientists sequence the genomes of gut microbes (collectively known as the microbiome) to study which types of microbes are present and in what quantities. They find that throughout life, the microbiome tends to become less diverse. They also find that some bacterial species within the intestines are associated with poor gut health and disease while others are associated with improved gut function, and that the latter may decline in favour of the former during ageing.
Studies have found that transplanting gut microbes from young animals into older ones can reverse some aspects of ageing, and not just in the gut. This study, for example, found that gut microbiota transplantation reversed cognitive decline in old mice. Unfortunately, less is known about whether human ageing can be slowed down by targeting the gut microbiota. Some studies have looked at the benefits of probiotic supplements, but these treatments are very different from transplanting the entire microbiota, as probiotics don’t contain human bacteria and don’t survive in the gut for long. While the importance of the gut microbiota in human ageing is being elucidated, we would all do well to improve and preserve the health of our gut microbes in any way we can. With that in mind, here are 11 factors that research suggests can modulate the health of the gut microbiota.
It seems that a diverse microbiota thrives on a diverse diet. Gut microbes play an important role in digestion and feed on the foods we consume. Studies suggest that eating a wide variety of plants is particularly important for fostering a diverse microbiota. The American Gut Study suggests aiming to eat 30 different plant foods each week. Some experts also suggest aiming to eat many different-coloured plants, as these tend to contain different nutrients.
Dietary restriction strategies such as fasting and calorie restriction appear to slow down age-related changes in the gut microbiome. Given the benefits of a diverse diet that we just discussed, the idea that eating very little food or nothing at all would also benefit the microbiota may seem counterintuitive. Low access to nutrients puts human cells into a ‘stress response mode’ that promotes repair and survival, and a similar beneficial response exists in bacteria. Dietary restriction also suppresses inflammation and improves the health of the intestinal barrier, which in turn benefits the gut microbiota.
Exercise – is there anything it can’t do? While the link is not as straightforward as with diet, exercise appears to benefit the diversity of the gut microbiota considerably. A variety of mechanisms explain this and are still being explored. Exercise reduces inflammation and improves function of the immune system long-term, which is important for the microbiota as it constantly interacts with immune cells in the gut. Exercise also protects against obesity (which is bad for the microbiota) while improving gut motility and digestion.
Prebiotics are nutrients (mostly fibres) that support the health of the gut microbiota. Fibre is a group of carbohydrates that humans cannot digest, but some fibre can be digested by gut microbes. Eating fibre-containing foods has been shown to support the growth of beneficial gut bacteria. Fibre also improves gut motility and relieves constipation, which leads to a healthier gut that in turn supports a healthier microbiota. Eating plenty of plant-based foods should ensure adequate fibre intake. Fibre supplements exist but aren’t a substitute for a plant-rich diet.
Probiotics are foods (particularly fermented foods like yoghurt and kefir) or supplements containing live, beneficial strains of bacteria capable of surviving the acidity of the stomach to reach the intestines. Some evidence suggests that probiotics show promise in preventing metabolic disease, but this evidence is quite inconsistent. One possible reason for this is that individual differences in diet and gut microbiota composition may render probiotics ineffective – those bacteria won’t do you any good if they have nothing to eat. Commercially available probiotic supplements also aren’t native to the human gut, which means they quickly get outcompeted by the microorganisms that are already there. This means that if you’ve lost diversity in your gut microbiota, probiotics will not be able to restore it to its previous, healthier state. Unfortunately, there’s currently only one way of restoring lost microbial diversity to the human gut…
A faecal microbiota transplant (FMT) is when a stool sample from a healthy donor is transplanted into a recipient, usually via colonoscopy. Microbes within the donor stool will then populate the recipient’s gut. Faecal transplants are used to treat recurring infections of C.difficile. However, transplanting stool from a young, healthy donor could also be used to restore the gut microbiota of older or diseased recipients to a youthful state. Faecal transplants are not without risk, though, as donor stool can carry infections and must be rigorously screened. Clinical trials are underway to study the wider applications of FMT, but there’s currently insufficient evidence to justify its use in treating any disease besides C.diff infection.
Stress can reshape the gut microbiota through a complex interaction between hormone balance, the immune system, and the central nervous system. Stress can increase inflammation and also appears to increase the permeability of the gut, both of which have negative effects on the composition of microbiota. Interestingly, this also seems to be a two-way relationship, meaning that an unhealthy gut flora may enhance anxiety and stress.
Studies suggest that good quality sleep correlates with a healthier and more diverse gut microbiota. This, once again, is most likely to work both ways. Sleep is vital for the health of the central nervous system, the immune system and also for the regulation of metabolism and digestion.
Some evidence suggests that artificial sweeteners may alter the function of some gut bacteria, impacting the way they break down certain nutrients and potentially even contributing to diabetes. While the debate still isn’t settled, there’s arguably enough evidence to justify cutting artificial sweeteners out of your diet. Artificial sweeteners do still seem to be better for you than sugar, though not by as much as you might think.
There are many reasons why you might wish to avoid ultra-processed foods. One reason is that many such foods contain emulsifiers, which are additives used to help oil and water mix together. The gut naturally produces emulsifiers, but some evidence suggests that ingesting emulsifiers used in processed foods may kill off beneficial bacteria in the gut.
There’s some evidence that environmental exposure to germs (such as from pets) may increase the diversity of the gut microbiome. However, this might only be relevant to children whose immune systems are still developing. It’s also not advisable to deliberately expose yourself to infectious agents, given that some of them can also disrupt the gut microbiota significantly.
Environmental exposure to pollution does appear to negatively impact the microbiota. Antimicrobial agents found within some care products may also reach the gut and kill off bacteria within. According to the FDA, products like commercially available antibacterial soaps may not be any better than regular soap for preventing disease.
It’s clear that the gut microbiota plays an important role in most aspects of human health. Armed with the knowledge presented here, we can all live a longer, healthier life with our symbiotic pals. Just remember that making sudden, large lifestyle changes can be detrimental and you should talk to a doctor about things like supplements and large dietary modifications.
Title image by CDC, Upslash
Microbiota from young mice counteracts selective age-associated behavioral deficits https://doi.org/10.1038/s43587-021-00093-9
American Gut: an Open Platform for Citizen Science Microbiome Research https://doi.org/10.1128%2FmSystems.00031-18
Gut Microbiota during Dietary Restrictions: New Insights in Non-Communicable Diseases https://doi.org/10.3390%2Fmicroorganisms8081140
Exercise Modifies the Gut Microbiota with Positive Health Effects https://doi.org/10.1155%2F2017%2F3831972
Prebiotics and the Human Gut Microbiota: From Breakdown Mechanisms to the Impact on Metabolic Health https://doi.org/10.3390%2Fnu14102096
Stress, depression, diet, and the gut microbiota: human–bacteria interactions at the core of psychoneuroimmunology and nutrition https://doi.org/10.1016%2Fj.cobeha.2019.01.011
Gut Microbiota in Anxiety and Depression: Unveiling the Relationships and Management Options https://doi.org/10.3390%2Fph16040565
Gut microbiome diversity is associated with sleep physiology in humans https://doi.org/10.1371%2Fjournal.pone.0222394
Personalized microbiome-driven effects of non-nutritive sweeteners on human glucose tolerance https://doi.org/10.1016/j.cell.2022.07.016
Randomized Controlled-Feeding Study of Dietary Emulsifier Carboxymethylcellulose Reveals Detrimental Impacts on the Gut Microbiota and Metabolome https://doi.org/10.1053/j.gastro.2021.11.006
Impact of Environmental Pollutants on Gut Microbiome and Mental Health via the Gut–Brain Axis https://doi.org/10.3390%2Fmicroorganisms10071457
Antibacterial Soap? You Can Skip It, Use Plain Soap and Water https://www.fda.gov/consumers/consumer-updates/antibacterial-soap-you-can-skip-it-use-plain-soap-and-water