Gut Health

Lifestyle tips to protect your gut

Diseases linked with poor gut health and the role for probiotics



‘The Gut’ is another word for the gastrointestinal (GI) or digestive tract, which starts at your mouth and ends at your rectum. A healthy gut is vital for effective digestion and absorption of food, enhancing  a state of well-being, regulating the immunity, avoiding illness in the gut itself and throughout the body.

Several factors can directly damage the gut including radiotherapy, chemotherapy, ingested chemicals, food allergies and food intolerances but the most important factors is the profile and diversity of the bacteria which live in our gut (The gut microbiome).

There are thousands of different species of bacteria and other organisms in the gut, collectively known as the gut microbiome. There are trillions of these bacteria in our gut as well as lungs, skin, genital tracks. In fact, it has been estimated that there is more genetic material from these foreign organism that than in our own cells. We are not talking about food poisoning (pathogenic bacteria) which causes acute illness but bacteria which colonise the gut for years. Put simply, some of these are  classed as “bad” as they can promote chronic inflammation  and others are classed as healthy or  “good” gut bacteria, because they reduce inflammation and work with the body to strength gut integrity (prevent leaky gut) improve gut and general immunity.  The section below explains and describes the diseases and symptoms caused by poor gut health  split into those which effect the gut and those which effect the rest of the body. In the mean time lets concentrate on ways we can support our gut:


Lifestyle measures to protect our gut’s “healthy” bacteria

There is still a lot we do not know about our microbiome –  scientist at the microbiome research centre in Cambridge University are discovering new strains every week. We are beginning to find out why the bacterial signature changes under different circumstances, how they effect disease risk and as you have just read above how they influence the response to treatments. Unhealthy bacteria tend to dominate more as people get older.  Here are the lifestyle and dietary factors which have been discovered so far:

 Non-nutritional factors:

  • Obesity
  • Smoking
  • Regular exercise can improve gut health, while extreme exhaustive exercise ca cause it to deteriorate
  • Depression and stress
  • Taking antibiotics
  • Taking antacids

Dietary factors

Foods are linked to poor gut health include:

  • High fatty meat intake
  • Excess alcohol – especially beer and spirits
  • Processed sugar

Healthy bacteria rich foods which  promote gut health:

  • Fermented and pickled foods
  • Live yoghurt, kefir,
  • Aged cheeses
  • Miso soup, tempeh,
  • Kimchi,
  • Natto,
  • Sauerkraut
  • A good quality probiotic supplement (see below)

Pre-biotic-rich foods which promote healthy bacteria

Certain foods can help promote the growth of healthy bacteria and impede the formation of unhealthy bacteria. Some, such as mushroom, have anti-biotic properties which directly kill unhealthy bacteria. These foods also protect bacteria from the enzymes in the saliva and stomach, enabling the formation of healthy colonies in the small bowel and colon. Pre-biotic-rich foods consist of two main categories

Soluble fermentable  fibres include Inulin; Starches such as sucoligosaccharides and fructooligosaccharide found in and other Polysaccharide beta-glucans. These are mainly found in:

  • Chicory, leeks and asparagus, onions garlic
  • Onions, asparagus, wheat, tomatoes beans and grains
  • Fruits, vegetables and mushrooms
  • Guar gum and psyllium.

Polyphenol prebiotics include plant lignans ; ellagic acid into ellagitannin

  • Nuts, bananas and beans
  • Citrus fruit such as pears, apples, cranberries, pomegranate
  • Beans such as chickpeas, peas, kidney beans
  • Vegetables and roots, broccoli, asparagus, chicory root and artichoke,
  • Grains and seeds such as barley, oats and linseeds
  • Resveratrol in grapes and red wine
  • Spices such as garlic, turmeric and chile
  • Tea and unsweetened chocolate

 The consequences of poor gut health

Excess chronic inflammation of the gut wall caused by too many pro-inflammatory (bad ) bacteria over time will thin and damage the integrity of the gut wall. The same problem occurs in people intolerant to foods such as gluten, lactose and lectin, because they have increased concentration of a gut protein called zonulin, which also signals the junctions to open up.

The adjacent picture shows that, in this situation, the increased, poorly functioning gaps between cells allows partially digested food and other harmful organisms to penetrate the tissue beneath it. This  poor gut integrity has been nick named leaky gut syndrome. This  weakened barrier not only  allows toxins, including carcinogens, into the bloodstream it causes  vitamins, minerals, polyphenols and proteins to leak into the gut depriving the body of the these essential nutrients. In the long term, levels of vitamin A, vitamin D and zinc are particularly affected, which are important elements in antioxidant and immune efficiency.

Gut symptoms and bowel disease:

Some people live with poor gut health for years without noticing although may have to take more medication such as antacids, anti-spasmodics and laxatives. Others  suffer from bloating, unsatisfactory bowel movements, excess offensive wind, pain, constipation and diarrhoea and indigestion. Poor microbiota reduces butyrate levels, which means less fuel for new cell growth. Consequently, the dead cells that are being naturally sloughed off cannot be replaced quickly enough, leading to a thinning of the gut wall. In severe cases, this can lead to ulcers, and if an ulcer is further irritated by acid in the stomach and duodenum, it can erode an artery, causing fatal bleeding. Poor gut health, in clinical studies, has revealed an increased risk of:

  • Food poisoning including Helicobacteria
  • Food intolerance
  • Food allergies
  • Stomach and duodenal ulcers
  • Inflammatory bowel disease
  • Bowel cancer

Symptoms and diseases outside the gut

The toxins which leak into the body unchecked trigger a chronic inflammatory reaction affecting the whole body the paradox is that this heightened non-specific inflammatory state stressed the immune system making it less efficient so individuals effected are more prone to infection from viruses and bacteria, more prone to immune related disorders and allergies. In this state the levels of chemicals called inflammatory cytokines are sky high and it’s a strange quirk of nature that these cytokines also encourage cancers to form and grow faster.

A leaky poorly functioning gut, was well causing gut related symptom and cause general distressing symptoms which have a significant impact on quality of life. In summary the symptoms and disease which may have an increased risk include:

  • Fatigue and low mood
  • More colds and flu
  • Arthritis
  • Osteoporosis
  • Diabetes
  • Cholesterol
  • Heart disease
  • Dementia and Parkinson’s disease

Gut health, cancer and response to cancer treatments

Gut health and cancer prevention: While it is clear that more research is needed, the evidence so far strongly suggests that a diverse bacterial microbiome can protect us from cancer by outcompeting (displacing) cancer-causing pathogens and reducing inflammation. There is also growing evidence that the immune responses to gut bacteria seem to help stimulate immune responses against cancer asa well. In addition, beneficial gut bacteria can counteract inflammation and strengthen anticancer immune responses not only in the gut but throughout the body.

Preliminary experiments in animals have found that stimulating growth of healthy bacteria in the colon leads to the inhibition of colon carcinogenesis. It has been suggested that this is due to their pH-lowering effect in the colon, which subsequently inhibits the growth of unhealthy (pro-inflammatory) bacteria such as E.coli and clostridia. A decrease in the growth of pathogenic microorganisms also modulates bacterial enzymes that convert pro-carcinogens to carcinogens. In humans, taking regular probiotics has been linked to a lower rate of new polyp formation and bowel cancer relapse. Probiotic bacteria help produce butyrate, an acid which feeds healthy gut wall cells but 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 has shown 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 fibre may increase butyrate production and slow tumour development. Besides fibre, healthy gut bacteria can convert polyphenols, into range of cancer-preventive chemicals including phenols and urolithins, produced from ellagic acid found in pomegranates and isothiocyanate, found in broccoli.

Therefore a high fibre and polyphenolrich diet can increase the abundance of cancer-preventive, butyrate-producing bacteria in the gut. On the other hand, a high-protein, low-carbohydrate diets,  changes 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 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 in relation to cancer treatments. Scientists have recently discovered that particular species of gut bacteria increase the therapeutic benefit of chemotherapy and the new targeted biological therapies for melanoma. These findings suggest that individual differences in microbiome composition may be one of the reasons these immunotherapies work better for some people than others. 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 T (immune) 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 unanswered questions, in the not so distant future, cancer care will likely include an analysis of the patient’s microbiome at diagnosis to inform personalised treatment planning. It may also be possible to manipulate the microbiome to optimise treatment outcomes.

Health Benefits of Probiotic Bacteria Supplements

Good bacteria can be ingested in foods such as fermented and pickled foods are especially good, and these include live yoghurt, kefir, aged cheeses, miso soup, tempeh, kimchi, natto, sauerkraut and pickled onions. Healthy bacteria can be significantly promoted by pre-biotics which help to feed them.

Scientist have been investigating the role for supplements containing healthy probiotic bacteria for years and there is still a lot which is unknown.

A supplement can be a convenient way to boost the diet but it is likely that if an individual has perfect gut health, then a regular probiotic supplement is not needed. On the the other, evidence there is going and strong evidence to show that that a well designed good quality supplement can help in many situations.

The rest of this  page highlights some of the potential roles for a probiotic/prebiotic supplement both for conditions in the gut and in the rest of the body:

Potential benefits of probiotic supplements inside the gut

Travellers diarrhoea: Certain strains of probiotics have been shown to be effective at treating diarrhoea and gastroenteritis commonly caught whilst travelling, usually from drinking water. 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 probiotics containing Lactobacillus significantly reduce the risk of nosocomial diarrhoea in infants, especially nosocomial rotavirus gastroenteritis.

Antibiotic-induced diarrhoea: Antibiotics play a vital role in treating bacterial infections but have the unfortunate side effect of also reducing healthy bacteria in our gut, altering the natural balance of the microflora, causing bloating and diarrhoea. A report published in the Journal of Pediatric Gastroenterology and Nutrition indicated that probiotics were helpful in the prevention or treatment of antibiotic-induced diarrhoea, especially in children.

Bacterial food poisoning: Most acute diarrhoea episodes are caused by viruses but some, especially those caught by ingesting infected food, can be bacterial. A study published in ‘Proceedings of the National Academy of Sciences’, found that probiotic bacteria can help protect against bacterial infections such as Listeria and the superbug Clostridium difficile infection. Some hospitals are giving people probiotics before going into hospital in order to reduce their risk of infection.

Brain function: A study involving mice conducted by the Alimentary Pharmabiotic Centre at the University of Cork demonstrated how 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 lactobacillus probiotics were reported to have improved brain function and less environmentally induced markers of stress.

Chemotherapy-induced diarrhoea: Several chemotherapy agents commonly cause diarrhoea due to damage these agents inflict on 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 bloodstream and, eventually, renal damage. A placebo-controlled randomised trial from Helsinki involving patients given 5FU chemotherapy to treat bowel cancer showed a highly significant reduction in the risk of diarrhoea among those given probiotics.

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 nutritionists agree that restoring the gut flora with a high-quality probiotic is a good idea, and some research even recommends an autofaecal transplant! (see paper)

Radiotherapy bowel problems: Several well-conducted trials have demonstrated that probiotics can help prevent radiation bowel damage and aid 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 several clinical studies which showed that probiotics can help some sufferers of IBS. 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 to take them continually.

Wheat and Lactose intolerance: As you get older, it’s common to develop an intolerance to gluten found in wheat and other grains. This causes IBS like symptoms with bloating and colicky pains. Reducing the intake of bread, pasta and cereals should always be the first measure taken, but a number of studies have demonstrated how probiotic intake can also be helpful. 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 a placebo. After one year, the probiotic group had fewer colds and, as a consequence, experienced less disruption to their training. 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 concluded that probiotics also reduce the incidence of upper respiratory tract infections. More recently it has been show that people with poor gut bacterial health has been linked to other respiratory disease such as asthma and worrying acute respiratory distress syndrome after flu infections such as SARS and Covid-19. – Read more about lifestyle factors to reduce the risks and consequences of a Covid-19 infection

Vaccinations: There are numerous studies which have reported that individuals who take probiotics around the time of a Flu vaccine and higher levels of anti-viral antibodies measured at a later date. Ongoing studies are investigating whether this applies to the covid vaccines – read more

Vitamin D absorption: As a fat soluble vitamin, the absorption of vitamin D is strongly linked to a healthy gut. A number of studies have linked the intake of a good quality probiotic supplement together with vitamin D supplements with higher blood levels of vitamin D3 [Jones]. Adequate vitamin D is important for a wide number of chronic disease including bone health and immunity – low levels have recently been linked to higher problems related to covid-19 [Jones].

Chronic inflammation: An overactive immune system leads to excess inflammatory cytokines which can cause numerous chronic diseases including arthritis, dementia, cancer and heart disease. The best anti-inflammatory diet is the macrobiotic diet, which features lots of fermented foods such as miso soup, kefir and kimchi. UK diets are traditionally 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 significantly. In another study, patients who took two probiotic capsules a day for 12 months experienced a reduction in the number of tender and swollen joints, while also displaying reduced inflammatory markers such as  IL-1β.

gut health rugbySports performance: Many athletes now take regular probiotic supplements. Alongside reducing the frequency and severity of “colds” avoids, mental alertness associated with a healthy gut can improve motivation to train. Reducing chronic inflammation can also help reduce joint pains and even damage associated with exercise. A study from Cork University has shown that elite rugby players have a much better gut profile than men in the general population at the same age.

Bone health: Probiotic bacteria Screenshot 2019-03-24 at 22.32.18have been shown to reduce gut inflammatory markers, and there is a known link between chronic gut inflammation and bone health. A number of laboratory studies have indicated that just 4-6 weeks of probiotics significantly increase bone density in animals with established osteoporosis or prevented its development altogether [Chiang, Yacon, Ohlsson].

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, on average, taking probiotics lowered systolic blood pressure by 3.56 mmHg and diastolic blood pressure by 2.38 mmHg. The greatest effects were seen in subjects with BP above 130/85 and those who took probiotics with multiple strains were more likely to experience a lowering of BP than those taking 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 evaluating humans, researchers recently discovered that Lactobacillus and Bifidobacterium probiotic strains prevented the accumulation of fat in the liver of obese rats. Markers of inflammation (tumour 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 either probiotics or a placebo. Mice who received the bacteria ate significantly less than the placebo group, 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 in turn 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 [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 the University of Cork reported in the journal Gut Microbes that Bifidobacterium may have benefits for patients with chronic fatigue syndrome.

Iron absorption: A trial from Gothenburg, Sweden published in 2015 showed that women taking a lactobacillus probiotic supplement were able to increase natural iron absorption from food [Hoppe]

Source information and references

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Other Reference sources for gut health:

How to Live” published by short books written by Professor Robert Thomas