Many of us are familiar with probiotics, such as certain yogurts and fermented foods, which are full of “good” bacteria that can support gut health.
You may have even heard of prebiotics, foods rich in complex carbohydrates (dietary fiber) that promote the growth of beneficial bacteria in the large intestine. Popular prebiotic foods include oats, nuts, and legumes.
But what about postbiotics? What are these and how do they affect our gut health?
What is a postbiotic?
Essentially, postbiotics are byproducts of the gut microbiota. In other words, your body produces postbiotics after digesting prebiotic and probiotic foods.
Examples of postbiotics include the short-chain fatty acids butyric acid (or butyrate), acetic acid (or acetate), and propionic acid (or propionate).
These molecules are produced when good probiotic bacteria break down dietary fibers from foods such as fruits and vegetables, grains and legumes.
These postbiotic molecules are important to your gut microbiota. Healthy probiotic bacteria thrive on these short-chain fatty acids in our gut.
And some postbiotics can help suppress “bad” bacteria. For example, probiotic bacteria (such as Lactococcus lactis) produce special chemicals called bacteriocins that can prevent pathogens such as E. coli from colonizing the gut. This process is known as “colonization resistance”.
Microbial fermentation is where microbes in the gut break down complex carbohydrates. Microbial fermentation of plant diets (rich in polyphenols), in particular, leads to the production of postbiotic phenylacetic acid. This postbiotic can reduce the growth of harmful pathogens in the body.
Not all postbiotics are good
However, not all postbiotics are heroes.
One type of postbiotic is bile acids, which are produced when we eat too many foods high in fat.
Bile acids have been linked to inflammation and colon cancer.
Long-term high-protein, low-carbohydrate diets often mean people don’t consume enough fiber, which is associated with a higher risk of colon cancer.
This may be due to the production of dangerous postbiotics such as bile acids.
What is the connection between postbiotics and cancer?
Our recent review (led by my colleague Kayla Jay from the University of Western Sydney) found that short-chain fatty acids – especially butyrate – showed promising results against breast and colorectal cancer cells in preliminary laboratory studies.
One clinical study found that patients with colorectal cancer produced significantly lower levels of short-chain fatty acids in their intestines than healthy participants.
Another study found that the number of bacteria producing short-chain fatty acids was low in premenopausal breast cancer patients.
Some cell and animal studies also report that postbiotic butyrate can help chemotherapy work better against breast cancer and regulate the immune system.
Epidemiological studies have reported that a diet rich in fiber, especially whole grains, may reduce the risk of colorectal cancer. This is mainly because diets rich in fiber lead to the production of short-chain fatty acids in the colon.
Ok, so what do I eat to get more postbiotics in my gut?
Dietary fiber is key.
Women and men should consume at least 25 and 30 grams of fiber each day, respectively. But few Australians follow this recommendation.
The best way to improve your levels of good postbiotics is to eat more vegetables, fruits, legumes, whole grain breads, nuts and seeds.
Jerusalem artichokes, garlic, onions, leeks and asparagus are fantastic prebiotic vegetables.
A diet rich in fruits and vegetables increases the levels of postbiotics, such as short-chain fatty acids, in the gut. It also helps reduce bile acids.
Gut health is about variety, which means eating a variety of fruits, vegetables, legumes, and whole grains to support a healthy gut microbiota.
You can also include fermented foods like sauerkraut and kimchi in your diet. These fermented foods have both prebiotic fiber and live probiotic bacteria that can help produce healthy postbiotics in the gut.
Of course, further research is needed. But to ensure good gut health, you should include plenty of fruits, vegetables, and legumes in your diet.
Deep Jyoti Bhuyan is a Research Fellow in Healthy Aging at the University of Western Sydney. This piece first appeared on Conversation.