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Aging and Gut Health: How Your Microbiome Affects How You Age

Your gut is home to trillions of microorganisms that are important for your overall health. Collectively called the microbiome, these bacteria, viruses, and fungi regulate your metabolism and immune system, while also protecting against harmful microorganisms. It’s through these functions that researchers believe they can affect how well you age. 

Research on the human microbiome, while still young, has expanded over the last couple of years thanks to the Human Microbiome Project and other initiatives. Thanks to these and similar projects, we now know that good health really does start with the gut and that decoding gut health may be the key to longevity. 

A Primer on Gut Microbes

While there are different kinds of microorganisms in your gut, bacteria take the lead and have attracted the most attention as a result. 

Researchers believe that there are about 40 trillion bacteria in your gut — about the same as the number of cells in your body. If you could collect all these bacteria at once, the amount you’d get would weigh around 200 g (0.4 lbs). That’s more than the weight of an adult’s kidney, spleen, or pancreas!

Given how big a place bacteria occupy in your body, it’s safe to assume that they are just as important as your organs. In fact, many researchers consider the microbiome to be an organ within an organ. Here are a couple of reasons why:

Aids digestion

Some strains of gut bacteria digest complex carbs that our digestive tract is incapable of breaking down. A certain species of Bacteroides, for example, was found to digest xyloglucans found in lettuce and onions.

Protects gut health 

Gut bacteria produce short-chain fatty acids like butyrate as a by-product of carbohydrate digestion. These fatty acids serve as an energy source for cells in your gut’s protective lining. These by-products were also found to be important in colon cancer prevention.

Regulates immunity

Gut bacteria help the immune system learn how to distinguish between harmful and helpful microorganisms. Gut bacteria communicate with your immune cells to help regulate immunity.

Having a rich and diverse microbiome was found to be good for health, while the opposite was found to increase a person’s risk of cardiovascular disease, inflammatory bowel disease (IBS), and autoimmune disorders. 

Changing Gut Microbes and Aging

Over a century ago, Élie Metchnikoff, a Russian zoologist noted for his pioneering research in immunity claimed that senility was the result of bacterial toxins leaking from the colon. This was the first time a researcher emphasized the importance of gut bacteria in healthy aging. 

Fast forward to today, researchers proposed that an unfavorable shift in the composition of gut bacteria (dysbiosis) in old age is behind common age-related problems like frailty, neurodegeneration, diabetes, heart disease, and cancer. 

Studies in mice and analyses of human fecal microbiota both seemingly confirmed this and show that the guts of older adults have fewer beneficial microbes (Bifidobacteria and Lactobacilli) and more pro-inflammatory microbial communities (Bacteroidetes and Proteobacteria). This change happens regardless of geographical location, diet, and lifestyle and is believed to be intrinsic to aging.

Aging leads to many changes, including in the intestinal barrier layer. The intestinal mucosa is thinner in seniors than in younger people, which may affect the number and diversity of gut bacteria. But not all of these age-driven changes are bad. According to several studies on centenarians — including over-100-year-olds in South Korea and Northern Italy — their changing microbiomes were linked to less inflammation and seem to contribute to their longevity. 

A Different Theory…

A study published in a 2021 issue of the journal Nature Metabolism is one of the first ones to claim that it’s not always a bad thing if your microbiome changes as you age.

The study in question compared data from over 9,000 people between the ages of 18 and 101 years old. The researchers' main focus, however, was on data from a cohort of more than 900 older individuals to track health and longevity outcomes.

Their findings confirmed that, yes, gut bacteria change with age. Before midlife, most people’s microbiomes are dominated by Firmicutes and Bacteroidetes. But after that, things begin to change and people develop divergent microbiomes with a decline in bacteria that dominate the guts of young adults. But what they also found is that the greater this change, the greater a person’s chance of entering old age healthy and living longer. 

Those with the most changes had higher levels of vitamin D and lower levels of triglycerides and LDL cholesterol. These lucky seniors were also more physically fit and took less medication. Conversely, those whose gut microbiome remained stable or changed minimally over their lifetime had more health problems and didn’t live as long.

The researchers proposed that bacteria that do us good in our youth could be harmful in old age because our metabolism and intestinal barrier change as we age. Bacteroides, for instance, are known to degrade the protective mucus lining our guts. While these bacteria are helpful when our intestinal mucus is thick and healthy in youth, its abundance in old age could “wear down” this protective layer and lead to widespread inflammation. 

On the other hand, a rise in rare bacterial species that produce unique metabolites linked to longevity (e.g. indoles and phenylacetylglutamine) also explains the longevity of some of the people in this study. 

How to Support a Healthy Microbiome and Live Longer

A healthy gut that will help you age well and live longer is something that’s completely attainable. While your gut microbiota is bound to change as you age, sticking to the golden rules of healthy living is bound to help keep your gut health:

Eat plenty of fiber

The Institute of Medicine recommends eating 19 to 38 g of dietary fiber per day, depending on age and gender. Good gut bacteria ferment dietary fiber to produce beneficial metabolites that keep your digestive tract healthy, your immune system strong, and inflammation at bay.

Don’t forget fluids

Some forms of dietary fiber are water-soluble, so make sure to take in 11 to 15 cups of fluids per day. Soluble fiber binds to bile in the gut, this way lowering blood cholesterol levels (bile regulates cholesterol production). It is also an essential type of fiber for the production of short-chain fatty acids. 

Stay active

Being physically active has an indirect effect on your microbiome as well. Exercise boosts mood, which can help you make healthier dietary choices. Exercise also increases vagal tone, which can lower inflammation in the gut and promote a healthier microbiome via the gut-brain axis. 


Aging is inevitable. But how you age is influenced by factors that are within your control. One such factor is the health and state of your microbiome. Research shows that older adults tend to have a different microbiome than younger counterparts, linking this change to their tendency to develop age-related diseases.

However, a different line of research proposes that some gut bacteria changes in old age are good and protect us from chronic diseases that can shorten our lifespan. Centenarians with a microbiome that’s very different from that they had in their youth can thank this change for their good health and longevity.

While we don’t yet know how the guts of centenarians got that way, we do know that eating a healthy diet that’s high in fiber and staying active are rules for healthy living that still apply when it comes to aging and gut health.




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