Health Benefits of Probiotic Bacteria
There are thousands of different species of bacteria and other organisms in the gut, collectively known as the gut microbiome. Some are classed as “bad” as they can cause acute diarrhoea or in the long term can promote chronic inflammation and leaky gut syndrome which increases the risk of premature ageing, degenerative and inflammatory disease. Healthy “good” gut bacteria, on the other hand, tend to reduce inflammatory and work with the body to improve gut and general immunity – helping to avoid bacterial and viral infections as well as lower the risk of food intolerances and food allergies. This page describes dietary and lifestyle factors which affect gut health.
The health benefits of probiotics supplements have not been completely determined but the results of published studies are increasingly compelling the most important of these are highlighted below.
Lifestyle measures which affect our gut probiotic bacteria
Non-nutritional factors: Regular exercise can improve gut health whereas there are links between obesity and depression and poorer gut health. Processes sugar directly feeds “bad” bacteria whilst polyphenols feed “good” bacteria.
Bacteria rich foods: Many foods contain healthy bacteria including fresh uncooked fruit and vegetables. Fermented and pickled foods contain the most. These include live yogurt, kefir, aged cheeses, miso soup, tempeh, kimchi, natto, sauerkraut and pickled onions. A good quality probiotic supplement can certainly help as they can 4-5 different strains and in high quantities but be careful of milk shots which ofter contain sugar and just one strain of bacteria and often have additional sugar.
Pre-biotic rich foods: These are food elements which help promote the growth of healthy bacteria yet impede the formation of unhealthy bacteria. Some, such as mushroom, have anti-biotic properties which directly kill unhealthy bacteria but not healthy types. Examples include fructooligosaccharide, which is included in the nature medical blend. They also protect the bacteria from the enzymes in the saliva and stomach so they can form the health colonies in the small bowel and colon. They have a low caloric value but have other potential health benefits. The two main categories include soluble dietary fibres (from linseeds, fruit grains etc) and polyphenol prebiotics (read more).
Potential benefits of probiotic supplements – inside the gut.
Travellers diarrhoea. Certain strains of probiotics have demonstrated positive results in treating diarrhoea and gastroenteritis commonly caught whilst travelling, usually from drinking water. In particular, a study published in the Journal of Pediatrics, concluded that Lactobacillus species are a safe and effective form of treatment for children with infectious diarrhoea. Other studies, have shown that prophylactic use of Lactobacillus containing probiotics significantly reduced the risk of nosocomial diarrhoea in infants, especially nosocomial rotavirus gastroenteritis.
Antibiotic induced diarrhoea. Antibiotics are obviously vital to kill unhealthy bacterial infection but, as a side effect, they also reduce the healthy bacteria in our gut altering natural balance of the microflora which can lead to bloating and diarrhoea. A report published in the Journal of Pediatric Gastroenterology and Nutrition showed that probiotics were helpful in the prevention or treatment of, antibiotic induced diarrhoea especially in children.
Bacterial food poisoning. Most acute diarrhea episodes are caused by viruses but some, especially those caught by ingesting infected food, can be bacterial. A study published in the prestigious scientific journal Proceedings of the National Academy of Sciences, found that probiotic bacteria can help protect against bacterial infection including Listeria and the super bug Clostridium difficile infection. Some Hospitals are giving people probiotics before going into hospital to reduce their risks of infection.
Chemotherapy induced diarrhoea. Some chemotherapy agents commonly cause diarrhoea due to damage to the cells lining the gut. If severe, as well as being very distressing and uncomfortable for the patient, this can lead to dehydration, concentration of the chemotherapy in the blood stream and eventually renal damage. A placebo controlled randomised trial from Helsinki involving 5FU chemotherapy for bowel cancer showed a highly significant reduction in the risk of diarrhoea. Other trials have reported benefits for analogues of 5FU such as capecitabine. Several ongoing trials are underway across the world including a large and significant one from Washington University School of Medicine.
After chemotherapy: Even without diarrhoea a course of intense chemotherapy can cause significant damage to the gut microbiome leading to multiple problems including malabsorption, fatigue and inflammation. Many oncologists and nutritionist are feel that restoring the gut flora with a good quality probiotic is a good is a good idea and some research even suggest autofaecal transplant! (see paper)
Radiotherapy bowel problems: Several well conducted trials have demonstrated that probiotics could help prevent radiation bowel damage and certainly help recovery after radiotherapy – click here for an example of a published trial
Irritable bowel syndrome (IBS) is a condition associated with abdominal bloating and flatulence. A 2010 Cochrane review summarised the evidence from clinical studies which showed that probiotics can help in some people. The National Institute for Health and Care Excellence (NICE) recommends taking them for at least four weeks, at a dose recommended by the manufacturer and if they work – continually.
Wheat and Lactose intolerance. As you get older it is common to develop an intolerance of gluten found in wheat and other grains. This causes IBS like symptoms with bloating and colicky pains. In the first instance it is advisable to reduce the intake of bread, pasta and cereals but a number of studies have demonstrated a helpful effect for probiotic intake. Intolerance to milk also is becoming more common, usually the result of a lactase deficiency. Lactase is an enzyme normally produced in your small intestine. It is needed to break down lactose and to enable you to digest milk. The probiotic Lactobacillus acidophilus helps with the digestion and absorption of lactose by producing lactase.
Potential benefits of probiotic supplements – outside the gut.
Viral respiratory tract infections (colds and flu). A study from Australia gave healthy athletes either probiotics or placebo. After one year the probiotic group had less colds and as a consequence had less disruption to their training. Athletes in Australia and across the world now take probiotics regularly. Several studies have shown that regular intake of live lactobacilli and bifidobacteria, shortened the duration and severity of upper respiratory tract infections. In 2011 a summary of all international studies was published in the prestigious Cochrane Database of Systematic Reviews, and concluded that probiotics also reduced the incidence of upper respiratory tract infections. The economic implications of these findings are enormous as the impact of colds is estimated to cost the United States $40 billion each year!
Chronic inflammation. A chronic over active immunity leads to excess inflammatory cytokines which can cause numerous chronic diseases including arthritis, dementia, cancer and heart disease. Although the Mediterranean diet is good the best anti-inflammatory diet is know has the macrobiotic diet which has lots of fermented foods such as miso soup, kefir and kimchi. UK diets are traditional low in these bacteria rich foods.
Arthritis. People with arthritis often have suboptimal gut health. One study gave a probiotic capsule to people with arthritis for 8 weeks and found that several markers of joint oxidative stress decreased insignificantly (ref). In another study patients who took two probiotic capsules a day for 12 months, compared to placebo had a reduced number of tender and swollen joints and reduced inflammatory markers such as IL-1β (ref).
Sports performance: Many athletes now take regular probiotic supplements and they believe the evidence that it improves the ability to train hence improve performance. There is a number of reasons for this. First reducing the frequency and severity of “colds” avoids breaks in training. Second, mental alertness associated with a healthy gut can improve motivation to train. Third, reducing chronic inflammation can help help reduce joint pains and even damage associated with exercise. There are a number of ongoing studies evaluating the sports enhancing benefits of probiotics but in the mean time a study from Coke University has already shown that elite rugby players have a much better gut profile than men in the general population at the same age.
Brain function. A study involving mice conducted by the Alimentary Pharmabiotic Centre in University of Cork showed that mice fed with Lactobacillus had significantly fewer stress, anxiety and depression-related behaviours than those fed with just broth. Moreover, bacteria fed mice had lower levels of the stress-induced hormone, corticosterone and had altered expression of receptors for the neurotransmitter GABA in the brain. In humans, a study from The University of California, showed that healthy women consuming probiotic-containing yogurt were reported to have improved brain function and less environmentally induced markers of stress.
Bone health. Probiotics bacteria have been shown to reduce gut inflammatory markers and there is a known link between chronic gut inflammation and bone health. In A number of laboratory studies, just 4-6 weeks of probiotics significant increase in bone density in animals with establish osteoporosis or prevented its development [Chiang, Yacon, Ohlsson]. There have been some trials in adolescence looking at pro and prebiotics calcium uptake which suggest increases in bone density [Abrams] and many authors are suggesting benefits for different age groups, which may well be the case although it would be advantageous to confirm this with randomised trials [Reid].
Blood Pressure. There is emerging evidence that probiotics may have a role in cardiovascular health. A meta-analysis of nine studies, published in the journal Hypertension, tracked over 543 adults with both normal and high blood pressure and found that taking probiotics lowered systolic blood pressure by 3.56 mmHg and diastolic blood pressure by 2.38 mmHg, on average. The greatest effects were seen in subjects with BP above 130/85. And those who took probiotics with multiple strains were more successful at lowering BP than single-strain sources.
Fatty liver and metabolic syndrome. Too much fat accumulating in the liver affects its function, eventually leading to damage. Several factors can cause a fatty liver, defined as fat stores >10% of its volume, including obesity, diabetes, alcohol abuse, poor diet and genetic susceptibility. Although there are no significant studies in humans, researchers recently discovered that Lactobacillus and Bifidobacterium probiotic strains prevented the accumulation of fat in the liver of obese rats. Markers of inflammation (tumor necrosis factor and interleukin 6) and triglyceride counts also improved. In another animal study, mice were fed a high fat diet for eight weeks and given probiotics or placebo. Mice who received the bacteria ate significantly less than the control mice, had lower insulin levels and body fat, and reduced their fatty liver deposits. Trials in humans are planned.
Obesity Obese patients usually have a poor microflora which promotes inflammation and storage of fats leading to further weight gain.A number of studies have demonstrated that some probiotics taken before a meal reduce overall calorie intake and reduce longer term body mass index [Hume]
Cholesterol levels. Research presented at the American Heart Association’s Scientific Sessions in 2012 reported that a formulation of Lactobacillus may be able to reduce blood levels of LDL (bad cholesterol).
Chronic Fatigue Syndrome. Scientists at University of Cork reported in the journal Gut Microbes that Bifidobacterium may have benefits for patients with chronic fatigue syndrome.
Probiotics, gut health and cancer
While it is clear than more research is needed, evidence so far strongly suggests that a diverse bacterial microbiome can protect us from cancer by:
- Outcompeting (displacing) cancer-causing pathogens
- Reducing inflammation
- Priming immune responses
There is growing evidence that the immune responses to gut bacteria seem to help stimulate immune responses against cancer. In addition, through molecular cues, such as cytokine IL-10, beneficial gut bacteria can dampen down inflammation and strengthen anticancer T-cell responses not only in the gut but throughout the body.
Preliminary experiments in animals found that a stimulated growth of bifidobacteria in the colon lead to the inhibition of colon carcinogenesis. It was suggested that this was attributed to the pH-lowering effect of bifidobacteria in the colon, which subsequently inhibited the growth of E. coli and clostridia. A decrease in growth of such pathogenic microorganisms also produce the modulation of bacterial enzymes that convert pro-carcinogens to carcinogens. In humans taking regular probiotics been linked to a lower rate of new polyp formation and bowel cancer relapse.
Healthy gut bacteria also produce butyrate that stimulates immune attach against cancer via T cells and helper T cells. Butyrate also exerts a direct effect on cancer cells, by turning off genes involved in cell growth and turning on genes that trigger cell suicide (apoptosis). Early research showed that butyrate can block the growth of colon cancer cells in vitro, and experiments in mice suggest that dietary intake of probiotics and/or prebiotics with soluble fiber may increase butyrate production and slow tumor development. Besides fibre, gut bacteria can use other dietary sources, particularly polyphenols, to produce a range of cancer-preventive chemicals:
- anti-inflammatory urolithins are produced from ellagic acid found in pomegranates.
- antioxidant equol is produced from daizdein found in soy-based foods.
- anti-inflammatory and cancer-blocking isothiocyanites are produced from glucosinolates found in broccoli.
- anti-inflammatory conjugated linoleic acid is produced from linoleum acid, a component of vegetable oils.
A fibre and polyphenol rich diet can increasing the abundance of cancer-preventive, butyrate-producing bacteria in the gut. High-protein, low-carbohydrate diets on the other hand may change fermentation in the intestine, leading to increased levels of harmful nitrosamines, and decreased levels of protective molecules like butyrate and phenols. Other research suggests that a high-fat diet can change the microbiome in a way that increases bacterial production of the bile acid DCA, which promotes colon and oesophageal cancers.
The microbiome and response to cancer treatments:
Laboratory and clinical studies are revealing a fascinating role for gut bacteria. The gut microbiome helps enhance the efficacy of immunotherapy. Scientists have recently discovered that particular species of gut bacteria increase the therapeutic benefit from CTLA-4 blockade (Bacteroides) in melanoma, while others enhance the effect PD-1 blockade (Clostridiales) and PD-L1 blockade (Bifidobacterium).8,9-11 These insights suggest that individual differences in microbiome composition may be one of the reasons these immunotherapies work better in some people than others.11,12
Scientists have a theory to explain the beneficial effects of gut bacteria during cancer treatment. Chemotherapy (cyclophosphamide and platinum salts) and immunotherapy can damage the intestinal lining, allowing certain types of gut bacteria and bacterial byproducts to leak into the blood circulation. Once they reach lymph nodes and lymphoid organs, these bacteria prime Th1 and Th17 T cells, which help recruit other immune cells to the tumour.
Microbiome research is a young, but fast-growing field. It is clear from animal and early clinical studies that the effect of the microbiome on cancer should not be discounted. While there are still many open questions, in the not so distant future, cancer care will likely include an analysis of the patient’s microbiome at diagnosis to inform personalized treatment planning. It may also be possible to manipulate the microbiome to optimize treatment outcomes.
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