In a previous article What are synbiotics? we spoke about some of the players in gut health. This week we will introduce a new term as we discuss: What are postbiotics?
What are postbiotics?
Postbiotics are metabolites (i.e. byproducts of metabolic processes) secreted by live bacteria or released by dead bacteria which provide health benefits to the host (1, 2).
Other names given to postbiotics are metabiotics, biogenics or metabolite/cell-free supernatants (1).
Types of postbiotics
Postbiotics include, but are not limited to:
- Short-chain fatty acids (SFCAs) produced by fermentation of non-digestible dietary fibre by gut bacteria. The most abundant SCFAs are acetate, propionate and butyrate (1, 2, 3, 4)
- Secondary bile acids (BAs), produced when by metabolism of bile acids synthesised by the host (1)
- Cell-free supernatants, essentially the medium used to culture bacteria and yeast which contains the metabolic products secreted by them but with the microorganisms removed (2, 3)
- vitamins, phenolic-derived metabolites, amino aromatic acids (2, 3)
- exopolysaccharides (biopolymers released from bacterial cell walls) (2)
- cell wall fragments such as bacterial lipotheichoic acid (2)
- enzymes such as glutathione peroxidase, peroxide dismutase, catalase and NADH-oxidase (2)
- bacterial lysates obtained by chemical or mechanical degradation of environmental bacteria (2)
- vanillic acid produced by metabolisation of anthocyanins (1)
- 10-oxo-12(Z)-octadecenoic acid (KetoA) produced by metabolisation of linoleic acid by lactic acid bacteria (1)
Health benefits of postbiotics
It is important to note that many of the health benefits attributed to postbiotics at this stage are based on animal and in vitro studies.
The SCFAs butyrate and propionate, as well as supernatants and cell wall fragments from Bacillus coagulans culture can exert a beneficial effect on the immune system (2).
Butyrate plays important roles in providing energy for colon cells, maintenance of the intestinal barrier and immunity (2, 5).
Exopolysaccharides can modulate the immune response and have antimicrobial and antioxidant properties. Kefiran may reduce cardiovascular risk factors. β-glucans may enhance the immune response, enhance the effects of probiotics and increase the bioavailability and absorption of carotenoids (2).
Galactosyllactose (3′-GL), a product of fermentation of human milk oligosaccharides can modulate the immune system and improve the intestinal barrier (2).
The cell wall component lipotheichoic acid may enhance the immune system, however it is possible that it might cause an excessive inflammatory response (2).
Bacterial lysates can stimulate the immune system, which has potential applications in childhood asthma, chronic obstructive pulmonary disease, allergic rhinitis and atopic dermatitis (2).
Antioxidant and anti-inflammatory properties
Exopolysaccharides can have antioxidant properties. Enzymes synthesised by bacteria, such as glutathione peroxidase, peroxide dismutase and catalase have antioxidant and anti-inflammatory properties (2).
3′-GL has anti-inflammatory properties (2). Butyrate can reduce inflammation in patients with ulcerative colitis (2, 5).
Treatment and prevention of allergies
Some postbiotics can prevent asthma exacerbation in children. Bacterial lysates can be an adjuvant in the treatment of atopic dermatitis in children. Butyrate can help prevent food allergies (2, 5).
Some postbiotics have antimicrobial effects, including exopolysaccharides and butyrate which helps regenerate the intestinal lining. Bacterial lysates can help reduce respiratory tract infections in children (2).
SCFAs are involved in glucose and lipid metabolism, energy balance and insulin sensitivity (4). More specifically, acetate is associated with insulin sensitivity, reduction of body fat and regulation of appetite in the central nervous system (2, 5).
Some postbiotics such as the secondary BA Deoxycholic acid, the SCFAs acetate and butyrate, vanillic acid and KetoA may have a positive effect on brown adipose tissue thermogenesis (i.e. heat production) and white adipose tissue browning (i.e. conversion to brown adipose tissue), both important for the reduction of body fat (1).
In addition, polyphenols metabolised by gut microbes may help reduce weight and insulin resistance (2).
Propionate may improve lipid profiles by inhibiting cholesterol synthesis (2, 4). Kefiran has anti-inflammatory properties and prevent the accumulation of cholesterol in macrophages. Bacterial lysates from Lactobacillus can reduce triglycerides and LDL-cholesterol and increase HDL-cholesterol (2). SCFAs can lower blood pressure (4).
Propionate can induce apoptosis (i.e. programmed cell death) in gastric cancer cells and regulate genes involved in cancer prevention (2).
Some postbiotics such as cell membrane vesicles can trigger autophagy of damaged organelles and proteins (2).
Other health benefits
Bacterial lysates can increase production of oxytocin, a neuropeptide that can accelerate wound healing (2).
Vitamins produced by gut bacteria include folate (important for DNA synthesis, repair and methylation), vitamin B12 (important for iron metabolism) and vitamin K (cofactor for blood clotting) (2).
Pros of postbiotics
The pros of postbiotics when compared to probiotics include:
- No risk of bacteria moving from the gut to the blood, causing potential issues especially in immunocompromised people
- No risk of acquiring antibiotic resistance
- Doses can be standardised
- Longer shelf life, easier storage and transport due to no need for refrigeration
Cons of postbiotics
Because postbiotics do not contain live bacteria, they don’t seem to have potential side effects (2). Having said that, as noted before some postbiotics which stimulate the immune system may cause a detrimental exaggerated immune response.
Summary and recommendations
Postbiotics include substances produced by the metabolic activity of gut bacteria or that are released by dead bacteria, which can benefit the host. What we know at the moment is promising but some areas of research require more experiments to guarantee efficacy and safety.
As a reminder, postbiotics are naturally produced in our bodies by a robust gut microbiome when provided with the right fuel. Hence, a healthy diet containing fermented foods and dietary fibre is likely to confer many health benefits without the need to rely on supplements.
- Reynés B, Palou M, Rodríguez AM, Palou A. Regulation of Adaptive Thermogenesis and Browning by Prebiotics and Postbiotics. Frontiers in physiology. 2018;9:1908.
- Żółkiewicz J, Marzec A, Ruszczyński M, Feleszko W. Postbiotics-A Step Beyond Pre- and Probiotics. Nutrients. 2020;12(8).
- Nataraj BH, Ali SA, Behare PV, Yadav H. Postbiotics-parabiotics: the new horizons in microbial biotherapy and functional foods. Microbial cell factories. 2020;19(1):168.
- Brial F, Le Lay A, Dumas ME, Gauguier D. Implication of gut microbiota metabolites in cardiovascular and metabolic diseases. Cellular and molecular life sciences : CMLS. 2018;75(21):3977-90.
- Berni Canani R, Paparo L, Nocerino R, Di Scala C, Della Gatta G, Maddalena Y, et al. Gut Microbiome as Target for Innovative Strategies Against Food Allergy. Front Immunol. 2019;10:191.
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