PUBLIC HEALTH
BACTERIA: THE GOOD, THE BAD AND THE UGLY More and more research is delving into the area of gut bacteria and its impact on health and disease, but whatâ&#x20AC;&#x2122;s good bacteria and whatâ&#x20AC;&#x2122;s bad and are probiotics the answer? As humans are born, their individual gut microbiota develops and is affected by the birthing process and early life. For example, whether an infant is breastfed or formula-fed, or whether the mother has taken antibiotics during pregnancy or lactation, it has been shown to result in a different balance of microbiota in the infantâ&#x20AC;&#x2122;s gut.3,4 Furthermore, differences in gut microbiota have been identified between those born via the vaginal canal or by caesarean section, though arguably other factors may be driving these differences, as critically discussed by Stinson et al.5 A multicentre European study by Fellani et al, found that breastfed infants had significantly higher proportions of Bifidobacteria (40.7% vs 29.2%, P<0.001) than formula-fed infants.6 Additionally, this study found that country of origin effected gut microbiota balance post weaning: infants from northern European countries had a higher proportion of Bifidobacteria, whereas infants from southern European countries had higher proportions of Bacteroides and Lactobacilli.6 It could be considered that the types of foods an infant is weaned on and their overall dietary intake will help determine which bacteria dominate for life. It is the foods eaten long term, along with other factors, such as environmental temperature and individual physiology,2 that play key roles in gut microbiota development. Once developed, the microbiota of an individual is quite stable for life. However, there are some factors that can lead to gut flora changes, for
example, antibiotic use, ageing, changes in diet such as drastic calorie changes, or altering macronutrient balance. Also, high-fibre diets are associated with increased diversity of microbiota.7 TYPES OF GUT BACTERIA
Numerous types have been identified in the human gut. However, the main two phyla are the Bacteroidetes and the Firmicutes.2 These two phyla differ in the efficiency of their metabolism. For example, a study by Turnbaugh et al showed that obese individuals and mice with a higher proportion of Firmicutes bacteria had a higher capacity to harvest energy.8 The study also showed that when the microbiota was transplanted from obese mice to germ-free mice, they rapidly gained fat mass, despite a decrease in food consumption. In another study, the abundance of Bacteroidetes was shown to increase as obese individuals lost weight on different low-calorie diets with a correlation that was significant.9 With obesity being a challenging and multifaceted health concern, it is important to address gut microbiota, as it may be a contributing factor, together with genetics, diet and lifestyle. Throughout the human gastrointestinal tract, the microbiota increases in both number and diversity, being affected by factors such as pH, transit time and nutrient availability.10 As the colon has the slowest transit time, a favourable pH and has plentiful available nutrients, the collection of microbiota is most varied and populated here. The intestinal microbiota has several beneficial roles:
Priya Tew Freelance Dietitian, Dietitian UK Priya runs Dietitian UK, a freelance dietetic service that specialises in social media and media work, consultancy for food companies and private patient work.
Naomi Leppitt Dietitian Naomi is newly qualified, working as a Community Dietitian in Windsor.
REFERENCES Please visit the Subscriber zone at NHDmag.com
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PUBLIC HEALTH Table 1. Types of intestinal microbiota found throughout the human gastrointestinal tract.10 Intestinal Microbiota Number Lactobacillus Streptococcus Staphylococcus Enterobacteriaceae Yeasts Clostridium Bifidobacterium Fusobacterium Bacteroides Eubacterium Peptostreptococcus
Stomach <103 CFU/ml ✓ ✓ ✓ ✓ ✓
Duodenum & Jejunum 102-105 CFU/ml ✓ ✓ ✓ ✓ ✓
• Metabolism: – Synthesis of vitamin K*, some water-soluble vitamins and all essential and non-essential amino acids.2 – Absorption of nutrients: - calcium, magnesium, iron; - lipid metabolism through bile acid metabolism.11 – Fermenting non-digestible carbohydrates, such as dietary fibre, resistant starches, cellulose, pectins, gums, unabsorbed sugars and alcohols:2 - Energy and other substrates can then be harvested and used. - Short-chain fatty acids are produced from the digestion of carbohydrate: butyrate has tumour suppressing activity,12 and this reduces levels of colonic cancer. *Escherichia coli and Salmonella enterica biosynthesise menaquinone-vitamin K2, which is an essential nutrient that humans and other mammals cannot synthesise themselves.13 • Immunomodulation: – Effects composition of the gut-associated lymphoid tissue (GALT): - Intestinal epithelial cells can avoid patho genic impact by signalling receptors of the innate immune system to bind to bacteria associated substances.2 In response, the body protects itself from pathogenic microbes. – Defence against harmful microbes by competing for binding sites on the intestinal wall, competing for available nutrients and by producing antimicrobial compounds.2 32
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Ileum & Caecum
Colon
103-109 CFU/ml ✓ ✓ ✓ ✓ ✓ ✓
1010-1012 CFU/ml ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓
THE BAD AND THE UGLY
Sufferers of IBS will be well aware of the side effects of certain bacteria. Some fermentable carbohydrates are poorly absorbed by the intestinal system. Upon ingestion of these FODMAPS, there is osmotic action, where fluid is drawn into the lumen of the colon,14 and they are also fermented by bacteria in the colon, producing methane and or hydrogen gas.15 Together, these produce the commonly experienced symptoms of bloating, flatulence, abdominal pain and loose stools. Evidence shows that disturbances to the microbiota may contribute towards IBS developing, with faecal analysis of individuals with IBS showing significantly lower amounts of Lactobacilli and Bifidobacteria and increased proinflammatory Enterobacteriaceae.16 A meta-analysis found the Bifidobacteria, Lactobacillus, Escherichia coli and Enterobacter were significantly altered between IBS patients and healthy controls.17 When the gut microbiota is imbalanced, research is revealing links with disease states. Examples include inflammatory bowel disease and conditions related to systemic inflammation such as Type 2 diabetes and obesity, as well as a tendency towards allergy.2 Food that isn’t sanitary can severely disrupt the composition of the microbiota, or cause small intestine bacterial overgrowth (SIBO), leading to chronic malabsorption of nutrients, chronic inflammation and increased intestinal permeability. This can then lead to systemic inflammation, malnutrition, faltering growth and stunting.18
PUBLIC HEALTH Allergies may be a result of altered microbiota composition in early life, through the hypothesis that this stimulates the immune system and ‘trains’ it to respond to antigens. But this happens disproportionately, leading to allergic reactions.2 Cardiovascular health is also related to microbiota, as described in a review by Tang et al: atherosclerotic plaques contain bacterial DNA the same as that found in the gut; metabolites generated by gut microbiota have been found to be a factor in the development of cardiovascular disease development. Microbiota may also have a role in blood pressure regulation; gut permeability results in bacterial translocation and systemic inflammation, which has been identified in patients with heart failure.19 WHAT ARE PROBIOTICS?
The term probiotic was first coined in the 60s and it was defined by the FAO/WHO and later updated as ‘live microorganisms that, when administered in adequate amounts, confer a health benefit on the host.20,21 Probiotics are classified according to their strain, as the effects of a particular bacteria are strain-specific and not always the same across all bacteria of the same species. However, benefit can be attributed to a whole class, such as Bifidobacterium or Lactobacillus.21 In addition, a probiotic must be seen, in controlled studies, to have benefits to health. Identifying and quantifying the health benefit to the host is a challenging area to research, due to the effects of probiotics being numerous and multifactorial and often through multiple mechanisms and sites of action. Probiotics are differentiated from gut bacteria by the fact they’ve been isolated and have credible health effects. Fermented foods are not considered probiotics, as though they may have health promoting effects, each batch may have different bacteria and in different amounts. Also, though evidence is expanding into the area of the health benefits of faecal transplants, these are not classified as probiotics as the bacteria differs from donor to donor.
HOW CAN THEY INFLUENCE THE GUT?
The mechanisms of probiotics are complex and depend on the strain and the site at which they act. For example, consensus research has shown that probiotics may compete with pathogens for essential nutrients, or for binding sites on the intestinal lining, they may produce antimicrobial substances, or short-chain fatty acids, improve transit, stabilise the intestinal barrier, or have roles in immunomodulation, or mucin production.10 The unique balance of microbiota in any individual is relatively stable and resistant to change, generally returning to normal after disturbances such as antibiotics, immunosuppression and other factors.10 During antibiotic therapy, the benefit of probiotics may have greater influence.10 The World Gastroenterology Organisation reports the guidelines for clinical recommendations based on evidence for probiotic use in different diseases.22 For patients with IBS that choose to try probiotics, NICE guidelines advise trying them for a minimum of four weeks, while monitoring the effects, at the dose recommended by the manufacturer.23 This is to test whether that probiotic beneficially alters microbiota composition resulting in alleviated symptoms. The BDA advise that probiotics may be unlikely to provide substantial benefits.24 Probiotics using lactic acid bacteria are considered safe as they have a long-term history of safe use in food.10 HOW CAN I PICK AN APPROPRIATE PROBIOTIC?
The International Scientific Association for Pre and Probiotics (ISAPP) recommends asking the following questions: Does it correlate to the dose used in studies? Does it provide an effective dose? Is it safe? What are the known health benefits associated with that strain? Does it provide the benefit being sought? Also, check the label. Does it give the full name of the strain; the number of live organisms in each dose (Colony forming units, CFU); the suggested dose; storage information and best before date; company information. Note: If an individual has acute pancreatitis of multiorgan failure, lactic acid is not advised. Probiotics and live yoghurts are also not advised for those on neutropenic diets. www.NHDmag.com October 2019 - Issue 148
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