The Role of Synbiotics in Cancer Care
What are synbiotics? They are a combination of probiotics, live microorganisms that have beneficial effects on us, and prebiotics, soluble fibre that we can't digest that feeds the microorganisms in our gut. They work together synergistically to improve our gut health.
How poor gut health raises cancer risk
Some strains of microbes benefit us, whilst others contribute to poor health. When the numbers of 'good' and 'bad' bacteria are out of balance, a condition known as dysbiosis, it causes inflammation in the body. This inflammation contributes to the cell conditions which cause a range of cancers to start: breast, colon, gastric, pancreatic, oesophageal, laryngeal and gallbladder (1).
Inflammation begins in the gut, where pro-inflammatory cytokines (messengers) produced by the 'bad' bacteria damage the lining of the gut. The junctions between the cells of the gut are supposed to be very strong to prevent the leakage of undigested food, toxins, bacteria and their metabolites (lipopolysaccharides or LPS) from the contents of the gut. The inflammation damages the junctions and permits that leakage, allowing these harmful substances to enter the bloodstream, where they set up even more inflammation (2).
One metabolite produced by certain bacteria, which are connected with consumption of large quantities of meat, is directly linked to changes in intestinal cells that can lead to colon cancer (2).
Other bacteria can convert bile acids, which are involved in fat digestion, into secondary bile acids. They are associated with several types of cancer (2). The ratio of primary to secondary bile acids can influence the composition of gut bacteria, which can affect the immune system, which is critical for the body's surveillance that prevents cancers from starting (2).
When you cook processed meat at high temperatures, some gut bacteria can convert the nitrites and amines in the meat to nitrosamines. Nitrosamines can damage DNA and are known causes of respiratory, bladder, liver, oesophageal and stomach cancers (2).
With gastric and oesophageal cancers, the problem often starts with an infection by Helicobacter pylori. H. pylori is present in about 50% of humans (3). But other microbes are involved in cancer development, as not everyone with H. pylori infection develops cancer in the stomach and oesophagus. Research shows that gastric cancer patients have a higher prevalence of H. pylori, as well as certain bacteria that cause inflammation, but eradicating H. pylori reduces gastric cancer risk (3), so it seems to be a case of symbiosis that adversely affects us.
Similar shifts in the composition of oral bacteria are associated with pancreatic cancer, where the researchers suggested they could be used as biomarkers to detect it. Interestingly, oesophageal cancers showed a reduction in the same bacteria (3).
The success of the HPV vaccine in reducing cervical cancer shows how eradicating the HPV virus is effective (2). However, again, not everyone who has the HPV virus develops cervical cancer. It needs oestrogen to develop. Intestinal microbes affect the amount of circulating oestrogen, so one study suggested that there might be a link to gut health in the development of cervical cancer (3).
Circulating oestrogen also increases the risk of breast cancer, so it's reasonable to assume that gut health plays a part there too (3).
HPV, along with H. pylori, seems to be linked with laryngeal cancer too. One study found increases in several strains of bacteria in laryngeal cancer tissue that they believe stimulate the inflammation that's involved in the cancer developing (3).
The research into synbiotics and cancer support
Using synbiotics helps the production of short-chain fatty acids (SCFAs) in the colon. These include butyrate, acetate and propionate.
Butyrate, in particular, has anti-cancer and anti-inflammatory properties. SCFAs help to maintain the strength of the intestinal barrier, preventing leaks and stimulate the production of mucus, which protects the intestinal lining (4).
SCFAs also help the immune system, which is so important to prevent cancers from starting, and protect the liver, the nervous system and the heart. They also have a role to play in weight management and preventing diabetes (4).
A randomised controlled trial (RCT) explored the effects of vitamin D and synbiotics in 76 breast cancer patients with their neoadjuvant treatment regime before surgery. Although the combination didn't result in eradication of the (non-metastatic) tumours, there was a significant reduction in their inflammatory markers, more than vitamin D and synbiotics individually. This suggested that the vitamin D and synbiotics together had protected patients against the highly inflammatory effects of chemo (5).
Fatigue is a major issue for cancer patients. A systematic review studied the evidence for probiotics and synbiotics in managing cancer-related fatigue. Two of the trials they studied showed that probiotics helped colon cancer-related fatigue. The other trial they identified revealed that synbiotics helped breast cancer patients manage their fatigue significantly better (6).
When colon cancer patients undergo surgery, they are very vulnerable to infection. Researchers tested the effects of synbiotics prior to patients undergoing colon cancer surgery. The synbiotic group had lower infection rates, shorter time of antibiotic use, lower inflammatory markers, and shorter hospital stays (7).
How to increase synbiotic intake
You can buy ready-made synbiotic capsules and one study suggested that this was more effective than taking probiotics and prebiotics separately. But people respond to fibre in different ways: some experience unpleasant digestive issues with certain types. As always, I believe it's preferable to use diet to supplement if you can, and there are foods that can provide synbiotics.
Kefir
If you can tolerate lactose, kefir is an excellent source of synbiotics. It is a fermented milk drink that contains a variety of helpful bacteria and yeasts, and the lactose in it is a prebiotic. It is associated with a reduced cancer risk.
No clinical trials have evaluated it yet, but in laboratory testing it killed glioblastoma cells. Kefir extracts were effective against chronic myelogenous leukaemia and colon cancer cells. Kefir also improved the effectiveness of doxorubicin against drug-resistant colorectal cancer cells (2).
Kimchi
If you enjoy spicy foods, kimchi is a traditional Korean dish made from fermented cabbage and/or Daikon radish.
A study found that Koreans who ate a traditional diet, as opposed to a Western diet, had lower rates of colorectal cancers (8). An animal study showed that it prevented colon cancer by upregulating tumour-suppression and antioxidant actions and downregulating inflammation (2).
In laboratory studies, it had anti-cancer effects against pancreatic and liver cancer cells (2).
Kimchi is fairly easy to make at home, and there are plenty of recipes online if you want suggestions. In Korea, every family has their favourite recipe, so keep looking until you find one that resonates with your tastes. If you buy it, look for refrigerated brands.
Miso
Fermented soybeans, salt, and a special yeast are used to make miso, which is a traditional Japanese food. It has a delicate umami flavour.
Miso contains a novel probiotic called Zygosaccharomyces sapae, which has anti-inflammatory properties. Consuming miso gives your immune system a boost (2).
A population study in Japan found that regular consumption of miso soup protected women from breast cancer, and the effect was highest in post-menopausal women (2).
They also discovered that it reduced gastric cancer mortality significantly (2).
In an animal study, adding miso to their diets reduced colon cancer risk (2).
Tempeh
Tempeh is a traditional Indonesian delicacy made from fermented soybeans. It has a chunky texture and tastes nutty.
Tempeh can inhibit angiogenesis, slowing cancer growth and metastasis, induce apoptosis in cancer cells, and is antioxidant (2).
Laboratory tests confirmed it can inhibit the growth of breast and colon cancer cells (2). Rats fed tempeh had lower levels of a certain bacterium that increases the risk of colon cancer (2).
Fermented pickled vegetables
Cucumbers and other vegetables fermented in brine also contain probiotic strains and the soluble fibre in the vegetables provides prebiotics.
These pickles contain substances that can have an anti-cancer effect, potentially preventing cancer cells from growing. They are effective at protecting against colorectal cancers (2).
You can ferment your own vegetables at home, not adding vinegar. If you choose to buy pickled vegetables, pick those in refrigerated cabinets rather than shelf-stable varieties. They pasteurize shelf-stable pickles to extend shelf life, killing the microbes you want to preserve.
Sauerkraut
Sauerkraut is a German dish made from fermented cabbage, very similar to kimchi but not spicy. It contains high levels of vitamin C and glucosinolates, which are known anti-cancer substances.
Cancer patients who eat sauerkraut have lower rates of cell mutation (2).
Its effects in the gut suggest that it has an immune-boosting effect. Women who eat sauerkraut have lower rates of breast cancer (2).
Other synbiotic foods
Sourdough bread and unsweetened plain yoghurt, staples of the Mediterranean diet, also contain synbiotics.
Alternatively, you can take a probiotic capsule and eat prebiotic foods, which are those high in soluble fibre. These include:
Beans: black, lima and kidney
Vegetables: Brussels sprouts, sweet potatoes, broccoli, turnips, carrots
Fruits: avocados, pears, figs, nectarines, apricots, apples, guavas
Nuts and seeds: flaxseeds, sunflower seeds, hazelnuts
Grains: oats, barley
Are synbiotics safe for a dairy-free diet?
Many people on a dairy-free diet avoid probiotics because they assume that Lactobacillus spp. contain milk in some form. Their name doesn't come from the fact they contain milk, but because many species of them grow well in milk products, where they use lactose (milk sugar) to form lactic acid (9).
One Lactobacillus species, L. rhamnosus GG, is used to treat cow's milk allergy in children (10). It is a species that cannot use lactose or casein as its source of energy, but produces lactic acid using other sugars.
As you have read above, probiotics grow in many foods besides dairy foods, and you can make your own synbiotics, such as yoghurt, by using non-dairy milks (11).
Are synbiotics safe for immunocompromised people?
Patients undergoing cancer treatment often suffer from a condition known as neutropaenia, which is defined as very low levels of neutrophils. Neutrophils are one of the most prolific immune cells and serve as the first defence against infections. They develop in the bone marrow, which is very vulnerable during cancer treatments. This means that cancer patients are often very susceptible to infections.
For many years, doctors have been reluctant to allow their cancer patients to take probiotics in case their compromised gut allowed bacteria to enter the bloodstream and cause infection.
Recently, research has found that, far from being dangerous, it prevents infections. In one, admittedly small, study on patients undergoing intensive chemo and a stem cell transplant, they received synbiotics together with enteral nutrition. Enteral nutrition is feeding via the digestive system, as opposed to via a vein. The synbiotic group had much shorter periods of diarrhoea, their appetites returned more quickly, and there were no infection problems (12).
Another trial on oesophageal cancer patients undergoing chemo prior to surgery had similar results. They concluded it prevented infections (13). A further study compared synbiotics with prophylactic antibiotics, and concluded that the synbiotics were more effective (14).
Conclusion
I recommend the use of synbiotic foods and supplements to help protect you against cancers starting and to support you during and after treatment. The digestive system gets badly damaged during cancer treatments, and they are a wonderful way to help it recover.
You can find much more dietary and lifestyle advice on cancer prevention and treatment support in my book, Naturally Supporting Cancer Treatment. If you would like to buy a copy, click on the Buy the Book button below.
References
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Rowaiye A, Ibeanu GC, Bur D, Nnadi S, Mgbeke OE, Morikwe U. Gut microbiota alteration - cancer relationships and synbiotic roles in cancer therapies. The Microbe. 2024;4:100096. doi:10.1016/j.microb.2024.100096
Brown LM. Helicobacter pylori: Epidemiology and routes of transmission. Epidemiologic Reviews. 2000;22(2):283-297. doi:10.1093/oxfordjournals.epirev.a018040
Xiong R-G, Zhou D-D, Wu S-X, et al. Health benefits and side effects of short-chain fatty acids. Foods. 2022;11(18):2863. doi:10.3390/foods11182863
Tirgar A, Rezaei M, Ehsani M, et al. Exploring the synergistic effects of vitamin D and synbiotics on cytokines profile, and treatment response in breast cancer: A pilot randomized clinical trial. Scientific Reports. 2024;14(1). doi:10.1038/s41598-024-72172-x
Belloni S, Caruso R, Giacon C, et al. Microbiome-modifiers for cancer-related fatigue management: A systematic review. Seminars in Oncology Nursing. 2024;40(2):151619. doi:10.1016/j.soncn.2024.151619
Polakowski CB, Kato M, Preti VB, Schieferdecker ME, Ligocki Campos AC. Impact of the preoperative use of synbiotics in colorectal cancer patients: A prospective, randomized, double-blind, placebo-controlled study. Nutrition. 2018;58:40-46. doi:10.1016/j.nut.2018.06.004
Park Y, Lee J, Oh JH, Shin A, Kim J. Dietary patterns and colorectal cancer risk in a Korean population. Medicine. 2016;95(25):e3759. doi:10.1097/md.0000000000003759
Garilli B, Southard C, Wojcik S. Lactobacillus acidophilus. University of Rochester Medical Center. 2025. Accessed March 18, 2025. https://www.urmc.rochester.edu/encyclopedia/content.
Tan W, Zhou Z, Li W, Lu H, Qiu Z. Lactobacillus rhamnosus GG for cow's milk allergy in children: A systematic review and meta-analysis. Frontiers in Pediatrics. 2021;9:727127. doi:10.3389/fped.2021.727127
Szparaga A, Tabor S, Kocira S, et al. Survivability of probiotic bacteria in model systems of non-fermented and fermented coconut and hemp milks. Sustainability. 2019;11(21):6093. doi:10.3390/su11216093
Mizutani Y, Kawamoto S, Takahashi M, et al. Efficacy and safety of synbiotics in patients undergoing autologous hematopoietic stem cell transplantation: A prospective, randomized, double-blind, placebo-controlled pilot study. Published online September 23, 2022. doi:10.21203/rs.3.rs-2071083/v1
Fukaya M, Yokoyama Y, Usui H, et al. Impact of synbiotics treatment on bacteremia induced during neoadjuvant chemotherapy for esophageal cancer: A randomised controlled trial. Clinical Nutrition. 2021;40(12):5781-5791. doi:10.1016/j.clnu.2021.10.004
Motoori M, Sugimura K, Tanaka K, et al. Comparison of synbiotics combined with enteral nutrition and prophylactic antibiotics as supportive care in patients with esophageal cancer undergoing neoadjuvant chemotherapy: A multicenter randomized study. Clinical Nutrition. 2022;41(5):1112-1121. doi:10.1016/j.clnu.2022.03.023
