Reviewing sources of energy from food and diet, we can see the contribution that carbohydrates can make as a source of fuel in the human body. We have also seen certain health impacts arising from the interplay between dietary fibre and the large intestine. Now, we can take a closer look to understand more precisely how this interplay exists and what it means for us when we consider our choices of food, looking at the potential benefits that those food choices can offer the human body. Before we can contemplate the choice of food and the effects that it has on our gut and state of health, overall, let us first consider the constituent part of the gut that interacts with the food and food components. The Large Intestine The large intestine is also known as the colon and it forms part of the gastrointestinal tract. It is a continuation of the small intestine and these two parts are housed within the abdominal cavity of the human body. Apart from the obvious characteristic of their sizes, a difference exists between these two parts that makes the large intestine quite distinct from the other parts of the gastrointestinal tract. The feature that makes the large intestine stand out is its incredible host of micro-organisms that remain resident in this region and the number of these micro-organisms keeps increasing as we get closer to the bottom end of the colon. One reason for this is the changing pH along the gut, as we move further away from the stomach area (which more acidic), so that micro-organisms can survive and thrive much more as we move further away from the stomach. The oxygen availability in the gut also decreases as we move further down the gut into the colon. This means that the micro-organisms that do exist in the large intestine are more likely to operate under anaerobic conditions (meaning devoid of oxygen). It is so incredible the number of micro-organisms that can exist within the large intestine, as many as one (1) trillion cells per gram. Isn’t that fascinating! These micro-organisms exist as bacteria, that is, the gut bacteria in the human body. So, why talk about the bacteria in our gut? Well, do you know, that even though we mostly consider bacteria as something disease-causing, bacteria that normally resides in the gut actually exert really beneficial effects on the body and these very bacteria are essential for our health and well-being. These can be considered the beneficial bacteria that reside in our gut. So, what do they do exactly? Well, the gut bacteria, the ones lining the large intestine, they provide protective, structural and metabolic functions in that region. These bacteria can sit on certain receptors or binding sites that line the wall of the intestine. What this means is that it blocks any other bacteria or harmful substance from sitting on these receptors. So, they act as a guard or a type of defence that prevents potential binding of harmful substances and blocks entrance into the blood and body systems that may later cause infection. Alternatively, these bacteria can also utilize nutrients in the region and thus deprive other potentially harmful bacteria of those nutrients. Assuming this competitive role against more harmful agents, these resident bacteria ensure a healthy presence within the gut. Importantly, the resident bacteria hold a strong position in ensuring that the walls of the large intestine are held in very close contact so that harmful agents are not able to move across the junctions of cells and enter the blood and body systems. Furthermore, these bacteria play a key role in immune function, having the responsibility of producing certain immunoglobulins and so contribute to the development of the immune system. These microbes thus serve as really important constituents within the region of the large intestine as it relates to our protection from potentially harmful microbial agents. We have also previously identified that these bacteria can also ferment certain substances found within the gut following consumption of certain carbohydrates, that is, the dietary fibre. We can recall that the dietary fibre is that substance that remain following consumption of carbohydrates that do not get broken down or absorbed in the small intestine, but just passes to the large intestine. It is this part of the carbohydrate that is indigestible but fermentable. And it is these bacteria in the large intestine that ferment the dietary fibre component of the carbohydrate. Following the fermentation process in the large intestine, the generation of Short Chain Fatty Acid (SCFA) such as a substance called butyrate may result and these products can act as a favourable source of energy for the gut lining and also helps to keep the walls intact and free of inflammation. At this point now, we can see the interaction at play. Interestingly, the food, that is what we eat, can influence the type of bacteria that we may find in the gut, placing emphasis in the large intestinal region. Indeed, throughout the stages of life, the resident bacteria are, for the most part, continuously changing. A new-born receives the microbes that exist in the mother’s breast milk and thus confers a specific type of bacteria that lines this naïve gut wall. However, as this child grows older and starts to consume more solid type foods, a greater variety of microbes may be added on to join the family residing in the gut. So, food, that is what we eat, has an influence as to what bacteria exist in our gut. It is worth noting though, that apart form food, stress and use of certain medicines, such as antibiotics can also unfavourably alter the bacteria that we may find in the gut region. So, if food has an influence on what lines our gut, then what does this mean for us exactly? So, now it is for us to figure out how exactly are we to receive, accept and allow these particular micro-organisms to live inside our large intestine. Well, there are two known ways through which we can achieve such an objective. That is through the consumption of foods that can be classed as prebiotics and probiotics. But what are these exactly? We can start with prebiotics PREBIOTICS One way of achieving the goal of allowing these micro-organisms to take residence inside our gut is through the consumption of prebiotics. Prebiotics is that constituent in food that are found in the dietary fibre part of the carbohydrate family. It is this quality that lets the dietary fibre go undigested to reach the large intestine. It helps to stimulate the growth, development and activity of the beneficial micro-organisms that reside in the gut. So, we see that the bacteria act on the dietary fibre through fermentation, but we can also see that the dietary fibre helps stimulate the multiplication and development of these bacteria. Isn’t that interesting! We have also seen the beneficial effects of this fermentation process: lowering blood cholesterol levels and control of blood glucose levels. So not only does the dietary fibre help with protection and immune function inside the human body, but it also exerts effects metabolically. Prebiotics have been shown to stimulate the growth and development of Bifidobacterium, one such bacterium that exerts the health benefits mentioned above. Sources of prebiotics: OLIGOSACCHARIDES: Fructo-oligo-saccharide Inulin Galacto-oligo-saccharide Xylo-oligo-saccharide These names represent the size of carbohydrate we are talking about. These structures may contain at least three to nine sugar units that are bound in really complexed ways and so makes these structures really difficult to be broken by enzymes in the small intestine. I want to highlight below the actual foods that carry this prebiotic and thus serves to augment functions of the beneficial micro-organisms within the gut. What these structures can do, once passed on to the large intestine, is to help grow bacteria in this region. Bifidobacterium is one such beneficial bacterium that can be grown and its activities stimulated by the presence of these complexed chemical structures. Food options: Note: with the consumption of legumes, that is peas and beans, it may be somewhat unfavourable for some persons as they may experience the unpleasant sensation of gas production. In this case, consideration of soaking the beans or peas overnight prior to cooking and consumption may help reduce the unpleasant effect of the gas production as this method helps to activate certain enzymes that can break down some of the fibre material that may responsible for the high volume of gas that can be produced. So how does prebiotic differ from probiotic? PROBIOTICS Well, unlike the prebiotic that stimulates growth and development of the beneficial bacteria in the gut, the probiotic consists of the actual strain or strains of bacteria in the food itself. So, the prebiotic does something to the gut, it helps multiply the bacteria there. The probiotics does its own provision of strains of bacteria. So, live strains are added to the gut directly from the probiotic type food. One way to remember this is that: [The PRObiotic PROVIDES the bacteria. It is the PROvider. With PREbiotics, there are already PRE-installed bacteria in the gut, they need only to multiply themselves and this multiplication effect is augmented by the prebiotic. So, prebiotics have their effects on the already PRE-installed bacteria in the gut.] Again, probiotics are those specially prepared foods that contain one or more live strains of beneficial bacteria, which when consumed in adequate amounts confer health benefits to the human body. You can find these types of food in your local supermarket or pharmacy. Additionally, they can be present in various forms, such as in the form supplements or as specially prepared foods such as yogurt or other dairy products. Two common species of beneficial bacteria include: Lactobacilli Bifidobacterium Probiotics has found its benefits as preventative treatment for Traveller’s diarrhoea, as populating the colonic environment with these bacteria makes competition for the more harmful type bacteria for which the body may be susceptible. There is a challenge though with the consumption of probiotics. Think about it. It has to enter the mouth and pass through the full length of the digestive tract before it can reach the large intestine. This means that the probiotic element of the food remains largely exposed to the horrific gastric acidic juices and stabbing enzymes of the stomach. How ghastly an experience! So, there is that gauntlet experience in the hope that the live strains still make it to the other end of the tunnel. Nonetheless, with the ones that do make it to the end, we can see exertion of certain health benefits. Perhaps, it may be worth noting that probiotics consumed over the long term may confer greater benefit. There is one further option that we can potentially apply, and that is to combine probiotic with prebiotic foods to obtain symbiotic effects. As a recap:
I hope that the information provided may be of value to you when considering the choice, purchase and consumption of foods that make up your diet. Additionally, if you are curious and want to know more, you can always talk with your local pharmacist, dietician or primary care physician and they can direct you further on what are some great options that you can consider in your local setting. References
Anderson JW. Dietary fibre, complex carbohydrate and coronary artery disease. Can J Cardiol. 1995 Oct;11 Suppl G:55G-62G. PMID: 7585294. Chen J, Raymond K. Beta-glucans in the treatment of diabetes and associated cardiovascular risks. Vasc Health Risk Manag. 2008;4(6):1265-1272. doi:10.2147/vhrm.s3803 Gandy J, Madden A, Holdsworth M. (2012). Oxford handbook of Nutrition and Dietetics. Oxford: Oxford University Press Geraldine O. Canny, Beth A. McCormick. Bacteria in the Intestine, Helpful Residents or Enemies from Within? Infection and Immunity Jul 2008, 76 (8) 3360-3373; DOI: 10.1128/IAI.00187-08 Macfarlane GT, Cummings JH. Probiotics and prebiotics: can regulating the activities of intestinal bacteria benefit health?. BMJ. 1999;318(7189):999-1003. doi:10.1136/bmj.318.7189.999 Sender R, Fuchs S, Milo R. Revised Estimates for the Number of Human and Bacteria Cells in the Body. PLoS Biol. 2016;14(8):e1002533. Published 2016 Aug 19. doi:10.1371/journal.pbio.1002533
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