December 2022
Probiotics: An Updated and In-Depth Review
If you’re like most people, you think of probiotics— “good” live bacteria that keep your gut healthy—as something that might be added to your yogurt or taken with antibiotics to protect your intestinal microbiome from being compromised.
This view of probiotics often extends to “prebiotics“—fiber-rich foods that the good bacteria in your gut “eat”—and “postbiotics”—substances released by the probiotics.
But as researchers study the relatively new science of gut microbiota, they’re finding that probiotics have many complex and valuable actions. Probiotics bio transform nutrients and fight toxins and pathogens in the body, they affect mood and body weight, and appear to sometimes prevent cancer and tumor progression, according to scientific research.
Anti-cancer effects have now been studied with colon, oral, breast, cervical, and pancreatic cancers.
How Do Probiotics Work?
According to a 2020 study in Biomedicine and Pharmacotherapy, key probiotic mechanisms of action include:
- binding, degradation, and inhibition of mutagen [an agent that changes genetic material]
- procarcinogen prevention and conversion of harmful, toxic, and highly reactive carcinogens
- gut pH lowering by short-chain fatty acids formed during degradation of non-digestible carbohydrate
- host’s innate immunity modulation and enhancement through secretion of anti-inflammatory molecules
When specifically fighting colon cancer, probiotics may have these mechanisms of action, according to a 2019 study in Oncology Reviews:
- enhancing the host’s immune response
- altering the metabolic activity of the intestinal microflora
- binding and degrading carcinogens
- producing antimutagenic compounds
- altering the physiochemical conditions in the colon
When it comes to fighting cervical cancer, a 2012 study published in the European Journal of Cancer Prevention found that probiotics were responsible for the following actions:
- normalization of gut microbiota
- decrease of harmful substances produced by intestinal bacteria
- enhancement of NK [natural killer]-cell activity
Moreover, the researchers wrote that the clearance of human papillomavirus (HPV)-related cervical lesions, which are related to cervical cancer in that the lesions often precede the cancer, is likely accomplished by the following actions of probiotics:
- reconstitution of vaginal (bacterial) microflora
- direct killing of pathogens
- competition for host-cell receptors
- interference with gene expression of pathogens
Clearly, probiotics aren’t a “one-trick” bacteria but have several actions that could help to fight cancers.
Cancer Diagnoses Are Growing
It should surprise no one that the diagnoses of cancers are growing. According to the Global Burden of Diseases, Injuries, and Risk Factors Study of 2019, 18.7 million people worldwide received a cancer diagnosis in 2010 compared with 23.6 million people in 2019.
The occurrence of cancer in people younger than age 50, called early-onset cancer, “has dramatically increased around the world, with the rise beginning around 1990,” according to The Harvard Gazette.
Yet, as those who have had cancer or had friends and family with cancer know, treatment is seldom a cure and can have disappointing results.
Not only does cancer have “no suitable cure existing till now,” according to the 2020 study in Biomedicine and Pharmacotherapy, but “the safety and stability of the standard chemotherapeutics drugs and synthetic agents used to manage cancer are doubtful.”
“Multi-drugs and hormonal chemotherapeutic agents not only kill the cancer cells but also damage the healthy cells and develop drug resistance. In addition, these cytotoxic drugs are associated with life threatening side effects that mostly result worse than malignancy of the cancer itself,” the researchers wrote.
Some of the cancers that have demonstrated encouraging results from treatment with probiotics include the following:
Colon Cancer
Colon cancer, or colorectal cancer (CRC), causes nearly 700,000 deaths each year, and only lung, liver, and gastric cancers are more fatal. Because of its human toll and probiotics’ localization in the intestines, the effect of probiotics on this type of cancer has been particularly studied.
“Accumulating evidence indicates that changes in the gut microenvironment, such as undesirable changes in the microbiota composition, provide favorable conditions for intestinal inflammation and shaping the tumor growth environment, whereas administration of certain probiotics can reverse this situation to a certain extent,” a 2020 study in Oxidative Medicine and Cellular Longevity reads.
“A double-blind test of synbiotics … [a mixture of probiotics and prebiotics] in 37 patients with CRC [colorectal cancer] and 43 colonic polypectomy patients [those who had colorectal polyps removed] demonstrated that the abundance of Lactobacillus and Bifidobacterium [two probiotics] increased, whereas that of Clostridium perfringens [a food poisoning-linked bacterium] decreased in CRC patients.”
In patients who had polyps removed, the researchers wrote that the “symbiotic intervention inhibited the colorectal cell proliferation ability and colon cell necrosis ability.”
Other researchers agree, writing in the journal Nutrients in 2019, “The prevention of colorectal cancer is associated with favorable quantitative and qualitative changes in the intestinal microbiota, as well as changes in metabolic activity and in the physicochemical conditions of the intestine.”
Cervical Cancer
Each year, 13,000 women in the United States are diagnosed with cervical cancer, and 4,000 die. Both the “Pap smear” and problematic vaccines such as Gardasil are designed to mitigate that number.
Research published in Clinical Nutrition ESPEN in April states that “numerous clinical studies have demonstrated the efficacy of probiotics in preventing cervical cancer, but their dosages, bacterial strains, and duration of therapy are somewhat inconsistent.”
A 2013 study in the European Journal of Cancer Prevention found that women who took probiotics had a “twice as high (60 percent compared to 31 percent) chance of clearance of their HPV-infection-related cytological abnormality as a control group.”
As noted earlier, HPV infections can progress into cervical cancer.
Breast Cancer
Each year in the United States, about 264,000 women are diagnosed with breast cancer, 42,000 of whom die.
The 2019 study in Oncology Reviews noted that probiotics show efficacy with breast cancer in an animal study.
“The results showed a significant increase in the survival time among the L. acidophilus [a probiotic] group compared to that of the controls, demonstrating that this treatment can promote the immune responses via stimulation of the production of pro-inflammatory cytokines such as IFN-γ [interferon gamma] and inhibition of the production of anti-inflammatory cytokines such as IL-4 [interleukin 4] and IL-10 [interleukin 10]. Additional animal studies confirmed that oral administration of L. acidophilus displays anticancer activity in mice bearing breast tumors,” the study reads.
In a 2020 study in the journal Cancers, researchers wrote: “Several in vivo and in vitro studies show remarkable evidence that diet, probiotics and prebiotics could exert important anticarcinogenic effects in BC [breast cancer]. Moreover, gut microbiota has an important role in the metabolism of chemotherapeutic drugs and in the activity of immunogenic chemotherapies since they are a potential dominant mediator in the response to cancer therapy.”
Some U.S. government clinical trials on the effect of probiotics in breast cancer treatment are underway.
Other Conditions That May Respond to Probiotics
Pancreatic cancer is one of the deadliest cancers, representing a high mortality rate. Yet probiotics may even offer hope with this cancer, according to a 2021 study in the journal Nutrients.
“The link between gut microbiota and pancreatic cancer has been intensively analyzed during the last several years,” the researchers wrote. “Alterations of gut microbiota affect pancreatic carcinogenesis. Microbes may affect the tumorigenic pathway.
“The supplementation of gut microbiota with methods, such as administration of prebiotics, probiotics, next-generation probiotics, synbiotics, and fecal microbiota transplantation may open new therapeutic strategies for pancreatic cancer patients.”
Addressing gut conditions may also be helpful with Parkinson’s disease, according to 2021 research in Frontiers in Aging Neuroscience.
“Accumulating evidence suggests that the onset of non-motor symptoms, such as gastrointestinal manifestations, often precede the onset of motor symptoms and disease diagnosis, lending support to the potential role that the microbiome-gut-brain axis might play in the underlying pathological mechanisms of Parkinson’s disease,” the reviewers wrote, addressing “existing evidence related to pre- and probiotic interventions.”
Rheumatoid arthritis has become an increasingly common diagnosis with many expensive medications advertised to treat it. However, more natural approaches with probiotics are also yielding encouraging results.
According to the Courtney Medical Group website, “In a 2014 study published in the journal Nutrition, 46 patients with rheumatoid arthritis (RA) were divided into two groups. One group received daily supplements containing Lactobacilluscasei and the other group received a placebo. After an eight-week period, several markers of inflammation were significantly lower in the probiotic group, leading researchers to state that, although further studies are needed to confirm the results, these conclusions may lead to the use of probiotics as an adjunct therapy for patients with RA.”
In another study, both patients with arthritic conditions and healthy patients saw a reduction in inflammation, which is very often behind pain.
Sources of Probiotics
While there’s a cornucopia of probiotic products at your grocery store or health food store, some foods also provide probiotics naturally:
- Sauerkraut
- Cottage cheese
- Yogurt
- Kefir (fermented cow, goat, or sheep milk)
- Kombucha (a fermented black or green tea)
- Miso (a soybean paste fermented with koji)
- Pickles (yes pickles! Cucumbers fermented with their own lactic acid bacteria)
- Olives (salt-water-brined olives contain the probiotics Lactobacillus plantarum and Lactobacillus pentosus)
- Sourdough bread
- Dark chocolate
- Kimchi (a Korean dish containing the probiotic Lactobacillus)
- Natto (soybeans fermented with the probiotics Bacillus subtilis)
Due Diligence
Probiotics are considered supplements so they aren’t regulated by the Food and Drug Administration. Therefore, as a consumer, you must do your “due diligence” when purchasing them.
For example, some suggest you stay away from store brands and buy probiotic brands that you recognize. Also, make sure the producing company uses good manufacturing practices—usually indicated on the label—in order to avoid potential allergens. And always check the expiration date.
A huge amount of probiotics are required for effectiveness—a billion “colony-forming units,” or CFUs. In addition to making sure your probiotic choice contains copious CFUs, it’s often recommended that you seek colonies that contain Lactobacillus, Bifidobacterium, Bacillus, or Saccharomyces boulardii—which are well-researched and highly regarded probiotics.
Also, since probiotics are actually living organisms, they should ideally be kept refrigerated because heat and improper storage kills microorganisms, including probiotics. If they aren’t refrigerated at the store where you buy them, that probably isn’t a good sign.
Some probiotics are encapsulated within foods such as inulins—plant-based polysaccharides (also called fructans) often derived from chicory—and this can be a good thing. When probiotics are wrapped in a food source such as inulin, it gives them something to “feed off of” and helps them to “remain viable while sitting on the shelf,” the Cleveland Clinic states.
Probiotics are available without a prescription, are reasonably priced, and are increasingly believed to have significant health benefits.