Until recently, it was thought that the trillions of bacteria that live in our intestines were just passive recipients of the food we ingest. We now understand that these bacteria function like another organ in the body, by impacting on digestion and absorption of food and influencing our immune systems. This community of micro-organisms is known as the gut microbiome. There are many thousands of different species of bacteria present in every individual, but the dominant species of bacteria can differ from person to person. Having an unhealthy mix of gut bacteria has been linked to obesity, diabetes, auto-immune disease and depression. Having a healthy balance of gut bacteria is also critical to healthy ageing. Luckily there are steps you can take to ensure a healthy gut microbiome.

What do gut bacteria do?

Gut bacteria partially digest our food, which increases the amount of nutrients that can be absorbed. A healthy variety of gut bacteria plays a key role in maintenance of nutrition. Some of these bacterial products actually are key nutrition sources for cells in the intestine and liver. These bacterial products also regulate appetite by increasing the release of hormones that give a feeling of satiety. The bacterial products of healthy bacteria even have an influence on the immune system by decreasing inflammation.

As people age, the gut microbiome changes and becomes less diverse. The dominant species of bacteria also change. These changes are related to things like hospital admission, antibiotic use and dietary changes. In particular, eating a diet that is low in fibre can deplete certain species of bacteria. Some of these changes may also be related to the physiology of ageing. As people age, there can be changes in the immune system that lead to constant low-grade inflammation, which may also influence the which bacterial species predominate. When there is less diversity in the gut, this gives the opportunity for bacteria to take over that can cause disease.

Not all people will have the same health status in older age. Older adults who have less physical reserve are described as frail. People who are frail are much more vulnerable to the development of new disability, from a seemingly minor insult. The cause of frailty is incompletely understood, but there is a strong association with inflammation, or inefficient activation of the immune system. Frail older adults have a much less diverse gut microbiome than robust older adults. This in turn might increase inflammation and lead to increased frailty. This can also lead to more disease causing bacteria growing in the gut which can lead to infections, like urinary tract infections and pneumonia.

What can you do?

We still have so much to learn about the bacteria that live with us. Most of the bacteria on our skin and in our gut require very specific conditions to grow so we have only begun to scratch the surface in understanding the large variety of bacteria present. Commercial probiotic tablets only carry a limited number of bacterial species, and as yet there is no evidence that these have any impact on ageing. The most promising approach to encourage a healthy gut microbe is not by focusing on specific nutrients, but by a whole diet approach. The Mediteranean diet, which has lots of legumes, vegetables, healthy fats like olive oil, seafood and little red meat, is associated with better cognitive function and longevity. There is currently research underway to look at the impact on balance of bacteria in the microbiome in a large European population.

The good news is that there are steps that you can take that can change your gut microbiome and bring back the health-giving bacteria. Bacteria reproduce very quickly and the rate of reproduction for a particular species of bacteria is influenced by whether its’ preferred ‘food’ is available. Eating the right foods to promote healthy bacteria can have a quick impact on the balance of bacterial species. Changing from a diet high in sugar and processed foods to one high in fibre can rapidly change the profile of the gut bacteria. High fibre foods include wholegrains, vegetables, fruit and legumes. Eating fresh, healthy food isn’t just delicious but will give you millions of tiny allies in the path to healthy ageing.